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Glass engineering - designing and making photochromic glass
WEBVTT Kind: captions Language: en
00:00:00.030 today on Applied Science I'm going to 00:00:02.09000:00:02.100 talk about designing and creating small 00:00:03.91900:00:03.929 batches of glass this is an unusual 00:00:06.14000:00:06.150 branch of engineering it's very unlike 00:00:08.12000:00:08.130 electrical or mechanical in that there's 00:00:09.89000:00:09.900 basically no information available how 00:00:12.04900:00:12.059 to get started in the home shop so today 00:00:14.57000:00:14.580 I'm going to summarize everything I've 00:00:15.82900:00:15.839 learned in the last couple months 00:00:16.84900:00:16.859 including reading out of print books and 00:00:19.09900:00:19.109 talking to glass experts and show you 00:00:21.23000:00:21.240 how to start having fun with this right 00:00:23.00000:00:23.010 away okay so let's check out some demos 00:00:25.42000:00:25.430 let's take a look at this unusual piece 00:00:27.74000:00:27.750 of glass I'm going to shine some light 00:00:29.17900:00:29.189 on it from this blue laser pointer that 00:00:31.66900:00:31.679 I got from eBay let's see what happens 00:00:37.93000:00:37.940 as you can see the glass is actually 00:00:41.78000:00:41.790 changing color when I shine light from 00:00:44.09000:00:44.100 the laser pointer in there and it's 00:00:47.38900:00:47.399 fairly responsive it changes in a few 00:00:49.31000:00:49.320 seconds this glass is actually 00:00:51.25000:00:51.260 photochromic so it's basically the same 00:00:53.29900:00:53.309 kind of glass that is used in sunglasses 00:00:56.56900:00:56.579 that change color when you go out into 00:00:58.36900:00:58.379 the Sun and some regions ever are a 00:01:00.74000:01:00.750 little bit more sensitive than others 00:01:02.06000:01:02.070 but you can definitely see what's going 00:01:04.07000:01:04.080 on here right let's try this one 00:01:11.71000:01:11.720 this one's also photochromic we can also 00:01:14.33000:01:14.340 give it a blast of light from this 00:01:16.03900:01:16.049 really big ultraviolet flashlight that I 00:01:18.62000:01:18.630 have here let's try this one out this is 00:01:20.89900:01:20.909 about the same wavelength 405 nanometer 00:01:23.14900:01:23.159 as the laser pointer it's just more it's 00:01:27.20000:01:27.210 just more of it there's there's more 00:01:28.76000:01:28.770 LEDs in here and then just for 00:01:30.62000:01:30.630 comparison this is like a modern 00:01:32.30000:01:32.310 photochromic lenses that these guys 00:01:35.03000:01:35.040 donated to the channel a long time ago 00:01:36.89000:01:36.900 just so you can see the performance 00:01:38.17900:01:38.189 difference so a modern this is actually 00:01:42.38000:01:42.390 a plastic lens and so it's not quite the 00:01:43.99900:01:44.009 same chemistry in here but you can just 00:01:45.64900:01:45.659 get an idea of of how it works with a 00:01:48.62000:01:48.630 modern photochromic lens dies in plastic 00:01:52.73000:01:52.740 as opposed to glass and now all of these 00:01:55.10000:01:55.110 are actually reversible so if we wait 00:01:56.81000:01:56.820 around long enough both the commercial 00:01:58.60900:01:58.619 lens and the glasses that I've created 00:02:00.64900:02:00.659 are they'll eventually go all the way 00:02:03.77000:02:03.780 back to their original state now in the 00:02:06.28900:02:06.299 commercial lens this happens in 00:02:07.76000:02:07.770 hopefully five to ten minutes in the 00:02:09.38000:02:09.390 glasses that I've created it's quite a 00:02:11.96000:02:11.970 bit longer 00:02:13.09000:02:13.100 could time-lapse this but it's really 00:02:14.44000:02:14.450 kind of like an overnight thing for this 00:02:16.30000:02:16.310 to translate back to its original 00:02:17.74000:02:17.750 clarity pretty cool though there's 00:02:21.04000:02:21.050 nothing special about this laser pointer 00:02:22.36000:02:22.370 I'll put links to everything as always 00:02:24.28000:02:24.290 in the in the description you can go on 00:02:26.32000:02:26.330 eBay and just pick up one of these laser 00:02:28.39000:02:28.400 pointers okay 00:02:30.31000:02:30.320 so that's this is actually making this 00:02:32.68000:02:32.690 piece of glass took a long time let me 00:02:34.78000:02:34.790 tell you most of the samples that you've 00:02:36.58000:02:36.590 seen on this table here were me 00:02:38.11000:02:38.120 attempting to make photochromic glass 00:02:40.06000:02:40.070 and it's taken a long time because 00:02:42.94000:02:42.950 there's a lot of variables involved here 00:02:45.25000:02:45.260 and I'm very happy to get this level of 00:02:47.92000:02:47.930 performance so this is not anything 00:02:50.32000:02:50.330 shocking I mean it's been around since 00:02:51.64000:02:51.650 the 1950s or 60s 00:02:53.26000:02:53.270 however I'll bet you have not seen a 00:02:55.30000:02:55.310 piece of glass that works quite like 00:02:57.07000:02:57.080 this one this one is also photochromic 00:03:00.31000:03:00.320 but as you can see the fade time is just 00:03:02.89000:03:02.900 seconds and so if I go across like this 00:03:05.44000:03:05.450 you can see it's there and then it fades 00:03:07.44000:03:07.450 this is actually an opal glass and so it 00:03:10.78000:03:10.790 it is a piece of glass it's just it's 00:03:13.39000:03:13.400 not transparent and it has this really 00:03:16.48000:03:16.490 weird property where you can draw on it 00:03:18.97000:03:18.980 and then it fades away almost instantly 00:03:21.16000:03:21.170 just a few seconds and the top has this 00:03:23.65000:03:23.660 weird kind of crystalline thing going on 00:03:25.45000:03:25.460 but it also works about the same way 00:03:27.46000:03:27.470 almost unfortunately this was a batch of 00:03:31.48000:03:31.490 glass that I made just by throwing a 00:03:33.16000:03:33.170 bunch of leftovers together in a pot so 00:03:34.99000:03:35.000 the point the formula for this one's 00:03:36.55000:03:36.560 unfortunately lost the time forever but 00:03:38.74000:03:38.750 the point is that I want to get everyone 00:03:40.75000:03:40.760 into hacking glass because with you know 00:03:43.57000:03:43.580 as many people hacking on electronics 00:03:45.37000:03:45.380 and mechanics if they were all hacking 00:03:46.69000:03:46.700 on making glass we would have all kinds 00:03:48.52000:03:48.530 of weird stuff by now so let's start 00:03:50.74000:03:50.750 talking about how to do this when I 00:03:54.52000:03:54.530 first got started with this project I 00:03:56.14000:03:56.150 thought what I would do is get a mold a 00:03:58.84000:03:58.850 glass mold dump all the ingredients in 00:04:00.76000:04:00.770 there with a mold release heat it up 00:04:02.29000:04:02.300 cool it and then pull out my finished 00:04:03.91000:04:03.920 piece of glass however it can never work 00:04:06.37000:04:06.380 that way unfortunately and the reason is 00:04:09.04000:04:09.050 that the glass batch when it's being 00:04:11.41000:04:11.420 formed like going from a mixture of 00:04:14.17000:04:14.180 powders into a finished piece of glass 00:04:15.94000:04:15.950 is extremely reactive and all of the 00:04:18.70000:04:18.710 mold releases that you can put in here 00:04:20.38000:04:20.390 will actually get sucked up into the 00:04:22.18000:04:22.190 glass batch and then you won't have a 00:04:23.59000:04:23.600 mold release anymore there's only one 00:04:25.96000:04:25.970 material on earth 00:04:26.94000:04:26.950 that won't stick to melting glass or 00:04:29.40000:04:29.410 forming glass and that's platinum and so 00:04:31.59000:04:31.600 they actually make tiny little platinum 00:04:33.15000:04:33.160 crucibles for doing laboratory glass 00:04:35.19000:04:35.200 analysis but that's a little expensive 00:04:37.89000:04:37.900 and apparently from what I've heard even 00:04:40.08000:04:40.090 then the glass doesn't just fall out I 00:04:42.03000:04:42.040 mean it still sticks in there and so if 00:04:43.80000:04:43.810 you're hoping to make like a nice you 00:04:45.51000:04:45.520 know good-looking puck of glass it's not 00:04:49.02000:04:49.030 gonna work forming it in a mold like 00:04:50.55000:04:50.560 this so I'll just cover that the mold 00:04:52.62000:04:52.630 releases quickly if you do make a custom 00:04:55.37000:04:55.380 blend of glass and then you want to form 00:04:58.11000:04:58.120 it into an interesting shape then you 00:04:59.67000:04:59.680 can use these conventional mold releases 00:05:01.65000:05:01.660 and most of these things came from like 00:05:03.66000:05:03.670 an art supply house for glass artists to 00:05:09.81000:05:09.820 popular kinds of mold release are this 00:05:11.73000:05:11.740 primo primer and this is a powder in 00:05:13.83000:05:13.840 here that you mix with water and it ends 00:05:15.87000:05:15.880 up making this fun purple solution and 00:05:18.06000:05:18.070 the purple is actually a useful thing 00:05:20.55000:05:20.560 when you're brushing it on your mold you 00:05:22.38000:05:22.390 can tell the spots that you haven't 00:05:23.94000:05:23.950 covered because they aren't purple so 00:05:25.41000:05:25.420 that's the point of that and then I also 00:05:27.45000:05:27.460 tried this really expensive boron 00:05:30.48000:05:30.490 nitride mold release this is actually 00:05:32.79000:05:32.800 really great stuff it's also fifty 00:05:34.47000:05:34.480 dollars it can and it works really well 00:05:37.26000:05:37.270 but again if you're making glass the 00:05:39.27000:05:39.280 temperatures are really high and the 00:05:41.07000:05:41.080 glass is very reactive and it will 00:05:43.35000:05:43.360 actually suck the mold release into the 00:05:46.29000:05:46.300 glass batch and that's actually what's 00:05:47.70000:05:47.710 happened here so this was a mold that I 00:05:49.95000:05:49.960 coated with that boron nitride spray and 00:05:52.56000:05:52.570 I put my ingredients in here and what 00:05:55.02000:05:55.030 happened this brown color is actually 00:05:57.06000:05:57.070 the boron nitride that's been 00:06:00.08000:06:00.090 incorporated into the glass and then 00:06:02.64000:06:02.650 after the glass was done eating away all 00:06:04.56000:06:04.570 of my mold release it proceeded to stick 00:06:06.63000:06:06.640 itself permanently to the mold which is 00:06:08.55000:06:08.560 alumina so what happened here is I 00:06:10.95000:06:10.960 basically just glazed the mold I started 00:06:12.87000:06:12.880 with this unglazed piece of alumina and 00:06:16.20000:06:16.210 now the glass is permanently fused in 00:06:18.30000:06:18.310 there so the way to do it is to get a 00:06:23.22000:06:23.230 melting dish and I'll put links again to 00:06:25.80000:06:25.810 all this stuff these are these you can 00:06:27.93000:06:27.940 actually buy these on Amazon they're a 00:06:29.43000:06:29.440 little expensive on Amazon if you get 00:06:31.59000:06:31.600 these imported you know from a Chinese 00:06:34.53000:06:34.540 seller on eBay it's just like a buck or 00:06:36.90000:06:36.910 two I mean it's no big deal 00:06:38.07000:06:38.080 and you can take these up to very high 00:06:40.14000:06:40.150 temperature 00:06:40.65000:06:40.660 and what you want to do is put your 00:06:42.09000:06:42.100 glass batch in here heat it up and then 00:06:44.31000:06:44.320 pour it out onto something else but 00:06:46.20000:06:46.210 we'll get into the details later also I 00:06:49.32000:06:49.330 should point out that you might have 00:06:51.18000:06:51.190 heard of float glass so commercially if 00:06:54.30000:06:54.310 you want to make like a big sheet of 00:06:55.62000:06:55.630 glass and make sure that it's really 00:06:57.06000:06:57.070 flat what can you do you don't want to 00:06:58.62000:06:58.630 put it through rollers because the 00:06:59.79000:06:59.800 rollers you know might Mar the surface 00:07:01.77000:07:01.780 or you have to adjust them to make them 00:07:04.65000:07:04.660 really parallel so the way the glass is 00:07:06.90000:07:06.910 made commercially is a giant vat of 00:07:09.06000:07:09.070 molten tin and they pour the molten 00:07:11.70000:07:11.710 glass on top of the Bolton tin and 00:07:13.95000:07:13.960 because gravity is makes things flat at 00:07:16.83000:07:16.840 the small scale here you're guaranteed 00:07:18.54000:07:18.550 that everything will be flat and uniform 00:07:19.89000:07:19.900 because you're dealing with liquids on 00:07:22.65000:07:22.660 the surface of the lake right it's going 00:07:24.06000:07:24.070 to be flat there's a couple of 00:07:26.52000:07:26.530 interesting crowded of course inside 00:07:28.89000:07:28.900 here I've got some tin I bought tin 00:07:33.42000:07:33.430 pellets on eBay and put them in my 00:07:36.45000:07:36.460 crucible here and melted it and then put 00:07:38.70000:07:38.710 some glass on top and you can see it it 00:07:40.71000:07:40.720 kind of almost worked but there's a 00:07:42.06000:07:42.070 couple of interesting problems one the 00:07:44.16000:07:44.170 tin oxidizes if you just heat it up in 00:07:46.26000:07:46.270 air so commercially what they do is have 00:07:49.62000:07:49.630 a giant furnace full of hydrogen gas 00:07:52.05000:07:52.060 where this liquid tin is hanging out and 00:07:54.81000:07:54.820 the hydrogen gas is very reducing it 00:07:57.42000:07:57.430 basically prevents oxygen from from 00:07:59.40000:07:59.410 being in there because if any oxygen got 00:08:01.14000:08:01.150 in it would react with the hydrogen so 00:08:04.53000:08:04.540 needless to say this is getting to be 00:08:06.06000:08:06.070 kind of difficult to do in the home shop 00:08:07.77000:08:07.780 having a 00:08:08.81000:08:08.820 molten tin with hydrogen gas and 00:08:11.25000:08:11.260 everything and then another interesting 00:08:13.17000:08:13.180 problem if you're making photochromic 00:08:14.94000:08:14.950 glass for example you can't do it in the 00:08:17.76000:08:17.770 float glass process because this glass 00:08:20.28000:08:20.290 is very sensitive to the environment 00:08:21.63000:08:21.640 it's in and it really doesn't like 00:08:24.21000:08:24.220 hanging out in a hot hydrogen 00:08:26.73000:08:26.740 environment because it actually prevents 00:08:28.26000:08:28.270 the glass from being photochromic so 00:08:30.65900:08:30.669 this can only be formed in crucibles or 00:08:34.08000:08:34.090 in oxidizing environments you can't use 00:08:36.18000:08:36.190 the float glass process for this so 00:08:38.70000:08:38.710 originally when I was having this 00:08:39.71900:08:39.729 problem with the glass sticking to the 00:08:41.37000:08:41.380 the molds and I was wondering what to do 00:08:43.17000:08:43.180 I thought well maybe I'll try this 00:08:45.15000:08:45.160 liquid metal idea since how could it 00:08:46.92000:08:46.930 stick to liquid metal and I would 00:08:49.59000:08:49.600 recommend not bothering with this at all 00:08:51.18000:08:51.190 as it turns out if you want to make a 00:08:52.47000:08:52.480 flat piece of glass in the home 00:08:54.15000:08:54.160 shaf there's easier ways to do it just 00:08:56.67000:08:56.680 forget the tin it's it's actually not 00:08:58.31900:08:58.329 that helpful if you're in a bind and you 00:09:03.18000:09:03.190 can't find or afford these aluminum 00:09:05.30900:09:05.319 melting dishes it's also possible to use 00:09:07.98000:09:07.990 porcelain so if you go to the store and 00:09:10.35000:09:10.360 buy you know dishware just plain old 00:09:13.86000:09:13.870 porcelain destroyed this can be okay the 00:09:16.25900:09:16.269 temperature that this can sustain is 00:09:17.87900:09:17.889 just barely high enough to do some glass 00:09:20.24900:09:20.259 experiments and we'll get about you know 00:09:22.74000:09:22.750 we can talk about making the glass melt 00:09:24.72000:09:24.730 at low temperature so that you can use 00:09:26.46000:09:26.470 porcelain melting stuff the one thing 00:09:29.16000:09:29.170 you have to be careful about is that if 00:09:30.74900:09:30.759 you buy dishware from the store it's 00:09:33.24000:09:33.250 already glazed right so there's already 00:09:34.74000:09:34.750 glass inside here on top of the 00:09:37.31900:09:37.329 porcelain you can feel the difference 00:09:38.81900:09:38.829 like if you touch this part of it it's 00:09:40.53000:09:40.540 typically not glazed so that's the raw 00:09:42.36000:09:42.370 porcelain and then inside it's already 00:09:45.32900:09:45.339 covered with glass so if you're making a 00:09:47.73000:09:47.740 glass batch and you pour all your 00:09:48.99000:09:49.000 ingredients in here it's going to be 00:09:50.55000:09:50.560 mixed along with whatever glaze the 00:09:52.29000:09:52.300 manufacturer already used whereas if you 00:09:55.23000:09:55.240 if you go with one of these unglazed 00:09:57.59000:09:57.600 melting dishes this is really raw 00:09:59.91000:09:59.920 there's there's nothing that this is 00:10:01.11000:10:01.120 going to contribute to your glass batch 00:10:02.57900:10:02.589 shirts 00:10:03.05900:10:03.069 it's the minimal amount okay so you've 00:10:07.43900:10:07.449 got your aluminum melting dish or your 00:10:09.62900:10:09.639 porcelain demitasse and you're ready to 00:10:11.67000:10:11.680 put it in the kiln to melt all the stuff 00:10:13.29000:10:13.300 down so let's talk about kiln selection 00:10:15.68900:10:15.699 first gas versus electric in this 00:10:19.13900:10:19.149 tabletop small scale size there are no 00:10:21.21000:10:21.220 commercial gas kilns so you'd have to 00:10:22.94900:10:22.959 make one but that's you know not the end 00:10:24.50900:10:24.519 of the world there's a couple other 00:10:26.16000:10:26.170 considerations though - you want your 00:10:28.55900:10:28.569 kiln to have really good temperature 00:10:30.72000:10:30.730 control like plus/minus 10 20 degrees C 00:10:33.35000:10:33.360 because a lot of making unusual parts of 00:10:36.56900:10:36.579 unusual kinds of glass involve heat 00:10:38.57900:10:38.589 treatment and annealing and you really 00:10:41.16000:10:41.170 do need good temperature control to do 00:10:42.84000:10:42.850 this so you know really fine temperature 00:10:45.87000:10:45.880 control with a gas kiln is it more 00:10:47.57900:10:47.589 difficult you probably need to like 00:10:49.07900:10:49.089 throttle the gas down not just turn it 00:10:51.03000:10:51.040 on and off to get good temperature 00:10:52.53000:10:52.540 control but the last consideration and 00:10:55.13900:10:55.149 sort of the most difficult one to get 00:10:56.57900:10:56.589 around is the atmosphere inside the kiln 00:10:59.42900:10:59.439 remember I was saying that having 00:11:01.28000:11:01.290 hydrogen atmosphere is no good for 00:11:03.48000:11:03.490 photochromic glass so they actually 00:11:05.00900:11:05.019 chemically hurt the glass and prevent 00:11:07.07900:11:07.089 it from being photochromic if you have a 00:11:09.60000:11:09.610 gas-fired kiln the exhaust from your 00:11:12.60000:11:12.610 flame is actually reducing there's 00:11:14.63900:11:14.649 probably quite a lot of carbon monoxide 00:11:15.86900:11:15.879 in there and at these temperatures that 00:11:18.44900:11:18.459 carbon monoxide will find oxygen 00:11:20.67000:11:20.680 molecules and react with it to make 00:11:22.71000:11:22.720 carbon dioxide and it's so reducing at 00:11:26.10000:11:26.110 these high temperatures that it will 00:11:27.48000:11:27.490 actually pull oxygen out of the glass 00:11:29.40000:11:29.410 and prevent it from being photochromic 00:11:32.24900:11:32.259 so I don't know I think commercially you 00:11:36.05900:11:36.069 could probably get around this by having 00:11:37.43900:11:37.449 like a really big crucible inside your 00:11:39.84000:11:39.850 gas-fired kiln and it's only the surface 00:11:42.09000:11:42.100 layer that's affected by the reducing 00:11:44.69900:11:44.709 atmosphere and a gas-fired kiln the 00:11:47.54900:11:47.559 trouble is if you're using small little 00:11:49.61900:11:49.629 melting dishes like this the amount of 00:11:52.13900:11:52.149 surface area appears high enough where 00:11:53.87900:11:53.889 if you've only got you know 100 grams of 00:11:55.55900:11:55.569 glass in here it's basically all going 00:11:57.84000:11:57.850 to be affected by the atmosphere in the 00:12:00.42000:12:00.430 kiln so using an electric kiln is very 00:12:02.85000:12:02.860 nice because temperature control is much 00:12:04.79900:12:04.809 easier and if you open the lid to the 00:12:07.29000:12:07.300 kiln you're guaranteed to have 00:12:08.68900:12:08.699 atmospheric air inside there later on 00:12:11.42900:12:11.439 you'll see there's so many variables 00:12:12.78000:12:12.790 involved with making a piece of glass 00:12:14.51900:12:14.529 that eliminating one more variable of 00:12:17.00900:12:17.019 having this unknown atmosphere from a 00:12:19.23000:12:19.240 flame in your kiln is another thing 00:12:21.21000:12:21.220 especially if you're turning the flame 00:12:23.10000:12:23.110 on and off to control the temperature 00:12:25.29000:12:25.300 now you're controlling also the oxygen 00:12:27.29900:12:27.309 level because the flame is on and off 00:12:28.71000:12:28.720 and so then there's more or less oxygen 00:12:30.17900:12:30.189 I would recommend definitely going with 00:12:32.51900:12:32.529 an electric this particular kiln here is 00:12:36.56900:12:36.579 called a muffle kiln and it's built kind 00:12:39.96000:12:39.970 of funny it almost seems like a DIY 00:12:42.38900:12:42.399 project itself it's basically just this 00:12:44.97000:12:44.980 helmet shaped thing and they can see the 00:12:46.82900:12:46.839 heating elements inside there and you 00:12:48.48000:12:48.490 can put it down on any surface you want 00:12:51.66000:12:51.670 and sort of turn that into a kiln this 00:12:54.09000:12:54.100 is the Paragon quickfire I bought this a 00:12:57.72000:12:57.730 long time ago it's not sponsored of 00:12:59.06900:12:59.079 course this is about three hundred 00:13:00.80900:13:00.819 dollars new I think and it's actually a 00:13:03.17900:13:03.189 really good solution the heating 00:13:05.30900:13:05.319 elements are rated to go up to about 00:13:08.29900:13:08.309 1050 degrees C but I've pushed it to 00:13:11.24900:13:11.259 1150 no problem one consideration is 00:13:15.21000:13:15.220 that it just comes with a switch 00:13:17.32000:13:17.330 so the the original temperature control 00:13:19.78000:13:19.790 is a switch that you turn on and off 00:13:22.12000:13:22.130 yourself and a analog temperature gauge 00:13:25.44900:13:25.459 here to tell you how hot it is and 00:13:27.37000:13:27.380 that's not going to work for doing a 00:13:28.99000:13:29.000 glassy treatment or annealing so what I 00:13:31.93000:13:31.940 did is I added this little pig 00:13:33.22000:13:33.230 controller here and you can set the 00:13:35.38000:13:35.390 temperature and it's actually amazingly 00:13:37.21000:13:37.220 good at reaching a temperature and 00:13:39.13000:13:39.140 holding it within just a few degrees 00:13:40.44900:13:40.459 even the reason that this kiln is 00:13:45.04000:13:45.050 limited to maybe 1150 C or even 1250 if 00:13:48.46000:13:48.470 you really really push it is because the 00:13:50.76900:13:50.779 heating elements themselves are made of 00:13:53.25000:13:53.260 nickel iron right nichrome and 00:13:56.81900:13:56.829 eventually it melts so it's a pretty 00:13:59.74000:13:59.750 hard limit on how hot you can get it 00:14:01.36000:14:01.370 because your heating elements eventually 00:14:02.56000:14:02.570 get so hot they melt so that that really 00:14:05.05000:14:05.060 does put a cap on things and 00:14:06.63900:14:06.649 unfortunately most silica glass patches 00:14:10.18000:14:10.190 have a rated like melting or forming 00:14:12.61000:14:12.620 temperature of like 14 or 1500 degrees C 00:14:15.61000:14:15.620 which is much too hot you'd never get 00:14:17.17000:14:17.180 your night chrome furnace that hot so 00:14:19.50900:14:19.519 what do you do well there are actually 00:14:21.43000:14:21.440 special electric furnaces that have 00:14:23.63900:14:23.649 heating elements that are not made of 00:14:25.69000:14:25.700 nichrome so the next level up from 00:14:27.67000:14:27.680 nichrome is silicon carbide is actually 00:14:31.09000:14:31.100 conductive and it melts at a higher 00:14:32.50000:14:32.510 temperature so they make heating 00:14:34.30000:14:34.310 elements out of that and then the top of 00:14:36.31000:14:36.320 the line is molybdenum disulphide very 00:14:39.46000:14:39.470 unusual material that's a blend of 00:14:41.38000:14:41.390 molybdenum and silica and they make 00:14:43.87000:14:43.880 these very very expensive small heating 00:14:46.84000:14:46.850 elements out of this material and you 00:14:48.57900:14:48.589 can get a kill on an electric kiln that 00:14:50.07900:14:50.089 goes up to fifteen or sixteen hundred 00:14:52.32900:14:52.339 degrees C the downside is that these 00:14:55.87000:14:55.880 kilns are really expensive even you know 00:14:58.21000:14:58.220 cheap import models on eBay sell for 00:15:00.51900:15:00.529 like two or three thousand dollars so 00:15:02.19900:15:02.209 you know it's in the context of this 00:15:04.51000:15:04.520 video it's really just kind of out of 00:15:06.01000:15:06.020 reach I wouldn't worry about it the nice 00:15:07.90000:15:07.910 thing is that you can make glass 00:15:09.46000:15:09.470 formulations that just don't require 00:15:11.07900:15:11.089 that kind of temperature so there's a 00:15:12.79000:15:12.800 lots and lots of experimentation you can 00:15:14.56000:15:14.570 do without father and with any of that 00:15:15.91000:15:15.920 and that's what we're going to talk 00:15:16.90000:15:16.910 about in this video this kiln originally 00:15:20.74000:15:20.750 came with its own shelf like its own 00:15:22.68900:15:22.699 bottom and you can see what happened 00:15:26.01900:15:26.029 here now remember I said that glass is 00:15:27.79000:15:27.800 very reactive so if you spill a little 00:15:30.28000:15:30.290 bit of 00:15:30.91000:15:30.920 glass batch on the Shelf here and then 00:15:33.61000:15:33.620 heated up to high temperatures it's 00:15:35.76900:15:35.779 actually dissolving away the material of 00:15:39.12900:15:39.139 the kiln itself so you have to protect 00:15:40.90000:15:40.910 the kiln and everything in there from 00:15:42.51900:15:42.529 your from your glass even spilling it is 00:15:45.19000:15:45.200 actually a very damaging like corrosive 00:15:47.74000:15:47.750 kind of event so luckily this this 00:15:50.80000:15:50.810 material is not super expensive and the 00:15:53.01900:15:53.029 nice thing about these muffle furnaces 00:15:55.15000:15:55.160 where you sort of pick the whole furnace 00:15:56.59000:15:56.600 up is that you can just have like a new 00:15:57.91000:15:57.920 bottom every month or whenever you need 00:15:59.98000:15:59.990 it so you can buy these fire bricks that 00:16:03.28000:16:03.290 are very lightweight and can take very 00:16:06.51900:16:06.529 high temperatures and are also 00:16:07.87000:16:07.880 insulating so I'll put links to all this 00:16:09.69900:16:09.709 if you search for fire brick be careful 00:16:12.12900:16:12.139 because some fire bricks are rated for 00:16:14.53000:16:14.540 high temperature but they aren't really 00:16:15.97000:16:15.980 insulating like it can withstand fire of 00:16:18.28000:16:18.290 it it's gonna get hot on the other side 00:16:20.13900:16:20.149 whereas it brick like this it could be 00:16:22.56900:16:22.579 you know 1,400 degrees C on this side 00:16:25.87000:16:25.880 and you could put your hand on this side 00:16:27.10000:16:27.110 and it would be no problem so to repair 00:16:29.47000:16:29.480 this kiln but I do this I just put two 00:16:31.18000:16:31.190 of these standard sized insulating fire 00:16:33.91000:16:33.920 bricks here and that's now my kiln floor 00:16:37.29000:16:37.300 another thing you can do to try to 00:16:39.37000:16:39.380 promote the life of your kiln floor is 00:16:41.19900:16:41.209 to cover it with this special kiln paper 00:16:43.36000:16:43.370 so they sell this stuff at the art 00:16:45.40000:16:45.410 supply stores and watch watch how it 00:16:47.05000:16:47.060 works 00:17:01.79000:17:01.800 pretty cool it's paper that doesn't 00:17:04.19900:17:04.209 really burn and so if you put glass on 00:17:06.99000:17:07.000 top of here this axe is sort of like a 00:17:08.88000:17:08.890 buffer layer and this will eventually 00:17:12.36000:17:12.370 become completely white ash and the 00:17:15.18000:17:15.190 glass won't be able to stick to the kiln 00:17:17.01000:17:17.020 floor because there's this layer of ash 00:17:18.63000:17:18.640 in between so pretty handy stuff just 00:17:21.72000:17:21.730 keep in mind though that if you pour 00:17:22.89000:17:22.900 your glass batch like if there's powders 00:17:24.54000:17:24.550 on here that are gonna form a glass they 00:17:26.81900:17:26.829 will dissolve the paper and the ash and 00:17:28.89000:17:28.900 everything else like we mentioned and 00:17:30.24000:17:30.250 eventually get all the way through so 00:17:31.56000:17:31.570 this is sort of a low-level way to 00:17:33.78000:17:33.790 protect yourself from spills you can see 00:17:36.60000:17:36.610 in my in my kiln here there's all kinds 00:17:39.09000:17:39.100 of remnants of ash here since I've been 00:17:42.45000:17:42.460 putting kiln papers on here to try to 00:17:44.01000:17:44.020 protect the top not 100% though because 00:17:46.38000:17:46.390 you can still see little errors here and 00:17:47.79000:17:47.800 there 00:17:48.15000:17:48.160 oh also you can use sort of a trivet so 00:17:54.00000:17:54.010 what will happen is the glass is very 00:17:56.58000:17:56.590 viscous and sticky and so if you've got 00:17:59.10000:17:59.110 your melting dish like this eventually 00:18:02.10000:18:02.110 you'll get some running down the side 00:18:03.84000:18:03.850 here it'll dribble down and if it's just 00:18:05.40000:18:05.410 sitting on top even with the kiln papers 00:18:07.38000:18:07.390 it'll eventually make a huge mess and 00:18:09.60000:18:09.610 destroy your kiln floor so you can put 00:18:11.85000:18:11.860 like a porcelain or alumina tray here so 00:18:14.37000:18:14.380 that when you put this down the drip is 00:18:16.32000:18:16.330 at least caught by that you keep the 00:18:17.91000:18:17.920 kiln floor living a little bit longer so 00:18:22.17000:18:22.180 we talked about making your glass batch 00:18:23.82000:18:23.830 in an alumina melting dish like this and 00:18:26.67000:18:26.680 then pouring it out on to a surface 00:18:28.29000:18:28.300 there's actually a really great material 00:18:30.03000:18:30.040 for doing this and that's graphite so if 00:18:32.76000:18:32.770 you go on eBay or Amazon you'll find 00:18:34.32000:18:34.330 there is these graphite Casting molds 00:18:37.08000:18:37.090 mostly for metal actually they weren't 00:18:38.70000:18:38.710 thinking that you'd use this for glass 00:18:40.08000:18:40.090 but you can and what I found to work 00:18:42.57000:18:42.580 really well is to get a mold of about 00:18:45.03000:18:45.040 this size and put it down like that you 00:18:48.27000:18:48.280 can use sandpaper to get the surface 00:18:50.34000:18:50.350 really flat and then use like a paper 00:18:52.02000:18:52.030 towel to polish it and then when you're 00:18:54.24000:18:54.250 getting ready to pour your glass what 00:18:55.89000:18:55.900 you do is you the surface up with a 00:18:58.62000:18:58.630 torch till you know it's maybe a few 00:19:00.81000:19:00.820 hundred degrees C or maybe even five 00:19:02.40000:19:02.410 hundred and then obviously there's gonna 00:19:05.67000:19:05.680 be hot open the kiln up and take your 00:19:08.37000:19:08.380 glass and pour it out onto the surface 00:19:10.38000:19:10.390 and the nice thing is that the graphite 00:19:13.33000:19:13.340 will not stick to your glass hardly at 00:19:15.70000:19:15.710 all I mean it's a really slippery 00:19:17.11000:19:17.120 surface what I found out doesn't work 00:19:19.69000:19:19.700 don't do this don't take the whole thing 00:19:22.18000:19:22.190 and put it in your kiln and then close 00:19:24.91000:19:24.920 the lid and heat the whole thing up to 00:19:26.35000:19:26.360 kill them temperatures the the graphite 00:19:28.03000:19:28.040 will survive 00:19:29.92000:19:29.930 but what will happen is the glass will 00:19:32.47000:19:32.480 rip off the top layer and it again 00:19:34.18000:19:34.190 incorporate the graphite into the glass 00:19:36.04000:19:36.050 because it's so reactive so that doesn't 00:19:37.87000:19:37.880 work okay so we've talked about the 00:19:42.22000:19:42.230 melting dish the kiln the mold release 00:19:44.08000:19:44.090 and everything what do we actually put 00:19:45.82000:19:45.830 in the dish to make this glass this is 00:19:48.49000:19:48.500 where things get really weird so if you 00:19:50.83000:19:50.840 search for patents about you know how to 00:19:53.47000:19:53.480 make weird kinds of glasses let's say 00:19:55.30000:19:55.310 photochromic glasses you'll find lots 00:19:57.58000:19:57.590 and lots of very detailed glass analyses 00:20:00.82000:20:00.830 right so you'll typically see let's say 00:20:03.61000:20:03.620 you find a glass analysis it's 50% 00:20:06.13000:20:06.140 silicon dioxide 00:20:07.72000:20:07.730 you know 40% boron trioxide 10% sodium 00:20:11.71000:20:11.720 oxide great I'll just get you know 50 00:20:14.71000:20:14.720 grams of silica 40 grams of or 8 and 10 00:20:17.56000:20:17.570 grams of sodium oxide and mix it all 00:20:21.25000:20:21.260 together and make a glass right not even 00:20:23.26000:20:23.270 close 00:20:24.64000:20:24.650 the ingredients that are that go into 00:20:26.86000:20:26.870 the glass batch do not have a whole lot 00:20:28.78000:20:28.790 to do with what comes out the other end 00:20:30.61000:20:30.620 and this may seem very strange but 00:20:33.70000:20:33.710 there's a really great analogy and 00:20:35.17000:20:35.180 that's in cooking so if you analyze the 00:20:37.72000:20:37.730 piece of cooked bread you would say it's 00:20:39.94000:20:39.950 you know 20 percent gluten 20 percent 00:20:42.61000:20:42.620 water whatever it is but if you're 00:20:45.04000:20:45.050 explaining how to make a blow for Fred 00:20:46.93000:20:46.940 to someone you wouldn't use those terms 00:20:49.12000:20:49.130 you would say start with flour and water 00:20:51.01000:20:51.020 and it's actually the process of making 00:20:53.20000:20:53.210 the bread that develops it into gluten 00:20:55.84000:20:55.850 and all the other finished products and 00:20:57.61000:20:57.620 that's that's exactly what's happening 00:20:59.38000:20:59.390 with the glass one trick with making 00:21:03.04000:21:03.050 these glass batches is that the 00:21:04.57000:21:04.580 temperatures are so high that almost any 00:21:07.12000:21:07.130 carbon is going to go away it's going to 00:21:09.70000:21:09.710 react with oxygen and leave the glass 00:21:11.86000:21:11.870 batch entirely so if we for example put 00:21:15.22000:21:15.230 in lithium carbonate when we heat this 00:21:17.68000:21:17.690 up to you know 1200 degrees C the co 3 00:21:21.04000:21:21.050 is going to go away and the oxygen is 00:21:24.34000:21:24.350 gonna there are some of the remaining 00:21:25.48000:21:25.490 oxygen 00:21:25.97000:21:25.980 is going to react with the lithium and 00:21:27.47000:21:27.480 we'll be left with lithium oxide in the 00:21:30.32000:21:30.330 glass so and then you might say well why 00:21:33.89000:21:33.900 not just start with lithium oxide the 00:21:35.72000:21:35.730 problem is that lithium oxide is really 00:21:38.03000:21:38.040 reactive and so if you put that in the 00:21:39.77000:21:39.780 glass batch it's very possible that as 00:21:41.93000:21:41.940 the thing is heating up all that lithium 00:21:43.88000:21:43.890 oxide is also going to go away before it 00:21:46.10000:21:46.110 has a chance to be incorporated into the 00:21:48.38000:21:48.390 glass batch so choosing ingredients to 00:21:50.90000:21:50.910 make a glass sort of requires you to 00:21:53.51000:21:53.520 find an ingredient that has a melting 00:21:55.37000:21:55.380 point and a stability that is compatible 00:21:58.07000:21:58.080 with all the other materials in glass 00:22:01.60000:22:01.610 luckily a lot of this work has already 00:22:03.71000:22:03.720 been done so if you sit down and you 00:22:05.45000:22:05.460 know you want to put lithium in your 00:22:06.91900:22:06.929 glass you pretty much use lithium 00:22:08.87000:22:08.880 carbonate there might be a few other 00:22:10.22000:22:10.230 chemicals that work too but pretty much 00:22:11.87000:22:11.880 it's always lithium carbonate and also 00:22:14.75000:22:14.760 for example if you want to add sodium to 00:22:16.58000:22:16.590 your glass pretty much using sodium 00:22:19.28000:22:19.290 carbonate is the way to go okay 00:22:21.78900:22:21.799 unfortunately there's not like a master 00:22:24.98000:22:24.990 table or anything that I have found that 00:22:26.84000:22:26.850 lists all the possible things you can 00:22:29.00000:22:29.010 put in I mean there's literally hundreds 00:22:30.35000:22:30.360 it goes on and on but to make sort of 00:22:33.89000:22:33.900 more normal kinds of glass it is pretty 00:22:35.96000:22:35.970 well figured out and I'll put as many 00:22:37.43000:22:37.440 links as I can in the description to 00:22:39.16900:22:39.179 help you out when you're just starting 00:22:42.35000:22:42.360 out and making a relatively simple kind 00:22:44.29900:22:44.309 of glass just plain old clear glass I 00:22:46.25000:22:46.260 would recommend is doing twenty grams of 00:22:48.59000:22:48.600 silicon dioxide 20 grams of sodium 00:22:50.99000:22:51.000 carbonate and 20 grams of boric acid and 00:22:54.32000:22:54.330 this will make you a borosilicate glass 00:22:56.99000:22:57.000 you've probably heard that term before 00:22:58.15900:22:58.169 it's the same kind of glass that's used 00:23:00.04900:23:00.059 in glassware and cooking dishes and all 00:23:02.65900:23:02.669 this kind of thing one benefit of 00:23:04.66900:23:04.679 borosilicate glass is that it is less 00:23:08.36000:23:08.370 sensitive to temperature fluctuation 00:23:10.52000:23:10.530 right like you don't want your glass to 00:23:11.96000:23:11.970 crack if you're heating up a test tube 00:23:13.43000:23:13.440 or something like that and similarly if 00:23:15.53000:23:15.540 you're making glass on your own you 00:23:17.41900:23:17.429 actually don't want it to be very 00:23:18.65000:23:18.660 temperature sensitive because you're 00:23:19.78900:23:19.799 gonna have to cool your piece of glass 00:23:21.08000:23:21.090 down from kiln temperatures all the way 00:23:22.85000:23:22.860 to room temperature and annealing is the 00:23:25.90900:23:25.919 process where you pick a temperature and 00:23:27.79900:23:27.809 hang there for a while to let the glass 00:23:29.45000:23:29.460 relax and sort of all the stresses 00:23:31.82000:23:31.830 dissipate and it typically takes hours 00:23:33.98000:23:33.990 for this to happen but having 00:23:35.89900:23:35.909 borosilicate glass you still have to 00:23:37.70000:23:37.710 anneal it but it's less 00:23:39.52900:23:39.539 sensitive than a non borosilicate glass 00:23:42.71000:23:42.720 or something that's more sensitive to 00:23:44.18000:23:44.190 temperature fluctuation mixing up all 00:23:48.22900:23:48.239 the powders is pretty important and it's 00:23:49.90900:23:49.919 something that I haven't spent a huge 00:23:51.10900:23:51.119 amount of time on but I probably should 00:23:52.77900:23:52.789 what I typically do is just have the 00:23:55.65900:23:55.669 container on the scale put all the 00:23:57.85900:23:57.869 powders in it and then sometimes I'll 00:23:59.62900:23:59.639 add these to brass balls and put the 00:24:01.63900:24:01.649 container lid on and shake it around and 00:24:03.56000:24:03.570 the balls will help sort of stir up the 00:24:05.69000:24:05.700 powder and actually kind of crush some 00:24:07.21900:24:07.229 of the crystals a little bit to mix it 00:24:08.77900:24:08.789 up 00:24:09.08000:24:09.090 in reality this could be a lot better 00:24:10.87900:24:10.889 any what you really want to do is put it 00:24:12.37900:24:12.389 in a rock tumbler and run it for a day 00:24:15.32000:24:15.330 or an hour or something like that and 00:24:17.14900:24:17.159 that will make sure that the powders are 00:24:18.61900:24:18.629 really really well mixed together and 00:24:20.97900:24:20.989 this is important because like we were 00:24:24.40900:24:24.419 talking about the glass batch doesn't 00:24:26.21000:24:26.220 just sort of all melt together it's 00:24:27.68000:24:27.690 actually a chemical reaction that's 00:24:29.14900:24:29.159 happening in there so you really want 00:24:31.19000:24:31.200 the powders to be in really really well 00:24:33.10900:24:33.119 mixed intimate contact with each other 00:24:35.11900:24:35.129 so that the chemical reactions can 00:24:36.58900:24:36.599 proceed as smoothly as possible if 00:24:39.73900:24:39.749 you've got a clump of something off in 00:24:41.33000:24:41.340 one corner of the crucible it's possible 00:24:43.75900:24:43.769 it will eventually melt and make a glass 00:24:45.76900:24:45.779 for you but it may not have the 00:24:47.59900:24:47.609 properties that you want because it 00:24:49.15900:24:49.169 didn't properly react with all the other 00:24:50.96000:24:50.970 ingredients and again think of a loaf of 00:24:53.11900:24:53.129 bread right like if you have a little 00:24:54.32000:24:54.330 chunk of unmixed flour or something in 00:24:57.08000:24:57.090 one corner of the pan yeah you'll still 00:24:59.45000:24:59.460 end up with a loaf of bread or something 00:25:00.71000:25:00.720 but it's not gonna be as good and funny 00:25:04.96900:25:04.979 enough the analogies with cooking 00:25:06.20000:25:06.210 continue this is actually a good 00:25:08.57000:25:08.580 ingredient to put in your glass just 00:25:10.19000:25:10.200 plain old table salt 00:25:11.47900:25:11.489 will add sodium and chloride and both of 00:25:14.71900:25:14.729 those are actually important in making 00:25:16.15900:25:16.169 photochromic glasses and so it's no joke 00:25:18.83000:25:18.840 that you know if your soup isn't very 00:25:20.02900:25:20.039 good what do you do you know you put in 00:25:21.49900:25:21.509 a pinch of salt same can be true of your 00:25:23.50900:25:23.519 batch of glass the main components of 00:25:27.10900:25:27.119 the glass are not super sensitive to 00:25:29.58900:25:29.599 variations in ratio so for example if 00:25:32.26900:25:32.279 your glass is 1/2 silica and about half 00:25:34.94000:25:34.950 bori you know getting it to be 4951 00:25:38.45000:25:38.460 isn't going to make any difference but 00:25:40.07000:25:40.080 when you're making them glasses that are 00:25:41.50900:25:41.519 photochromic or have like a very 00:25:42.88900:25:42.899 sensitive chemical aspect to them some 00:25:45.46900:25:45.479 of the ingredients are very sensitive 00:25:48.08000:25:48.090 and the quantities are just absolutely 00:25:49.82000:25:49.830 tiny so for example in the photochromic 00:25:52.24900:25:52.259 glass 00:25:52.71000:25:52.720 this copper oxide needs to be added 00:25:55.34000:25:55.350 about point oh eight percent I think and 00:25:59.13000:25:59.140 so measuring out such a teeny amount 00:26:01.11000:26:01.120 even with a balance that's capable of 00:26:02.78900:26:02.799 measuring milligrams is very challenging 00:26:04.66900:26:04.679 so what you do is you dilute the 00:26:07.64900:26:07.659 sensitive ingredient in one of the base 00:26:09.87000:26:09.880 ingredients so for example for this 00:26:11.52000:26:11.530 borate glass I'm using boric acid as 00:26:14.46000:26:14.470 like the main batch component and so 00:26:16.98000:26:16.990 what I would do is take half a gram of 00:26:18.41900:26:18.429 copper oxide and mix it with 20 grams of 00:26:21.09000:26:21.100 borate and so I'll have this very dilute 00:26:24.14900:26:24.159 sort of copper oxide powder and then you 00:26:27.84000:26:27.850 can measure this out with also still 00:26:30.00000:26:30.010 pretty good precision but not quite the 00:26:31.47000:26:31.480 precision that you need to measure the 00:26:32.73000:26:32.740 oxide by itself let's finish up by 00:26:36.33000:26:36.340 talking about the actual chemical 00:26:38.15900:26:38.169 ingredients that go into this 00:26:39.45000:26:39.460 photochromic glass sort of as an example 00:26:41.82000:26:41.830 and I'll try to describe and generalize 00:26:43.71000:26:43.720 what these ingredients do so this 00:26:46.04900:26:46.059 winning combination that I've got here 00:26:48.14900:26:48.159 this photochromic glass has this recipe 00:26:51.77900:26:51.789 it's 22 B as you can see I spent a long 00:26:54.53900:26:54.549 time tweaking different components of 00:26:57.51000:26:57.520 the recipe there are a lot of variables 00:26:59.70000:26:59.710 involved here not only is the ratio of 00:27:02.27900:27:02.289 ingredients important but also the speed 00:27:05.54900:27:05.559 at which you bring them up to the 00:27:06.72000:27:06.730 melting temperature in the kiln and then 00:27:09.06000:27:09.070 how long you hold it at that temperature 00:27:10.62000:27:10.630 and then when you pour it out of the 00:27:12.75000:27:12.760 kiln you let it cool down to room 00:27:14.31000:27:14.320 temperature and then bring it back up to 00:27:16.28900:27:16.299 a forming temperature to actually create 00:27:19.20000:27:19.210 this photochromic property and then of 00:27:21.33000:27:21.340 course that has a time and temperature 00:27:22.62000:27:22.630 associated with it as well and the 00:27:24.69000:27:24.700 atmosphere and the kiln during the melt 00:27:26.31000:27:26.320 process and then the atmosphere during 00:27:27.87000:27:27.880 the heat treat process and it just goes 00:27:29.49000:27:29.500 on and on so I'm not claiming that this 00:27:31.89000:27:31.900 is tweaked it down to perfection in fact 00:27:33.96000:27:33.970 far from it this will just give you an 00:27:35.58000:27:35.590 idea of what's going on and sort of the 00:27:37.47000:27:37.480 the challenges that you'll encounter if 00:27:38.94000:27:38.950 you end up doing this I should also 00:27:41.64000:27:41.650 point out that a lot of the patents 00:27:43.28900:27:43.299 around photochromic glass talk about a 00:27:46.16900:27:46.179 lot of these times and temperatures but 00:27:48.06000:27:48.070 they'll say things like the heat 00:27:50.07000:27:50.080 treatment may be conducted between 500 00:27:52.44000:27:52.450 and 700 degrees C for between ten 00:27:55.28900:27:55.299 minutes and two hours now what will 00:27:57.45000:27:57.460 actually happen is that the heat 00:27:59.22000:27:59.230 treatment only works between 600 and 600 00:28:02.39900:28:02.409 twenty degrees and it must be between 30 00:28:04.50000:28:04.510 minutes and 40 minutes 00:28:05.91000:28:05.920 but of course they want the patent to be 00:28:07.44000:28:07.450 as broad as possible and if there's some 00:28:09.03000:28:09.040 weird way you can make it work outside 00:28:10.80000:28:10.810 those parameters then fine but they're 00:28:13.17000:28:13.180 definitely not describing the easiest 00:28:15.36000:28:15.370 way to make it they're describing all 00:28:17.01000:28:17.020 the possible ways to make it and so 00:28:19.11000:28:19.120 that's kind of another problem with the 00:28:20.31000:28:20.320 patent system is that it's you write 00:28:23.07000:28:23.080 them to be overly broad but anyway okay 00:28:25.32000:28:25.330 let's get down to business here with the 00:28:26.73000:28:26.740 chemicals this winning combination is a 00:28:28.92000:28:28.930 borate glass there's actually no silica 00:28:31.29000:28:31.300 in it whatsoever so it's not 00:28:32.61000:28:32.620 borosilicate it's just for Oh borate 00:28:35.28000:28:35.290 glass so we've got 20 grams of boric 00:28:38.04000:28:38.050 acid this will contribute b203 or borate 00:28:41.67000:28:41.680 in the final glass and this is kind of 00:28:43.20000:28:43.210 the backbone of the whole system then we 00:28:46.50000:28:46.510 have 2.2 grams of aluminum hydroxide now 00:28:50.37000:28:50.380 remember the hydrogen is going to go 00:28:51.96000:28:51.970 away at these high temperatures and 00:28:53.91000:28:53.920 we're going to be left with al 2 O 3 so 00:28:56.25000:28:56.260 alumina which is dispersed among the 00:28:58.77000:28:58.780 mixture and the function of alumina is 00:29:00.72000:29:00.730 just to stabilize the glass structure we 00:29:05.76000:29:05.770 don't want it to diva trophy which means 00:29:07.89000:29:07.900 convert from a glass into a crystalline 00:29:09.78000:29:09.790 structure and this helps with that this 00:29:12.27000:29:12.280 ingredient also calls for calcium 00:29:13.89000:29:13.900 carbonate which again the carbonate is 00:29:15.87000:29:15.880 going to go away and this is going to 00:29:17.10000:29:17.110 become calcium calcium oxide in the 00:29:19.65000:29:19.660 final glass and this is also a 00:29:21.54000:29:21.550 stabilizer that makes the glass less 00:29:24.72000:29:24.730 dissolvable like less prone to being 00:29:27.36000:29:27.370 broken down by the environment I know 00:29:29.52000:29:29.530 that sounds silly for a glass that we 00:29:31.44000:29:31.450 only care about you know I just want 00:29:33.09000:29:33.100 this to work in the lab I don't care if 00:29:34.44000:29:34.450 this survives for years and years but 00:29:36.81000:29:36.820 again I was following a recipe and I got 00:29:39.69000:29:39.700 this thing locked in and I couldn't 00:29:40.98000:29:40.990 change this variable easily because I 00:29:42.84000:29:42.850 was too busy changing other variables 00:29:44.88000:29:44.890 basically then we have 0.4 grams or 0.3 00:29:50.10000:29:50.110 grams in the winning mixture of silver 00:29:52.23000:29:52.240 nitrate this is actually the same 00:29:54.45000:29:54.460 chemical that works in old-fashioned 00:29:56.85000:29:56.860 black-and-white photography and it's 00:29:58.26000:29:58.270 actually the same mechanism inside the 00:29:59.94000:29:59.950 photochromic glass so what happens is we 00:30:02.67000:30:02.680 mix silver nitrate with sodium chloride 00:30:05.43000:30:05.440 in this glass mixture and then as it's 00:30:08.55000:30:08.560 reacting as the glass is being formed 00:30:10.47000:30:10.480 these things trade places and we end up 00:30:12.54000:30:12.550 with silver chloride and sodium nitrate 00:30:15.18000:30:15.190 and the sodium nitrate gets burned down 00:30:17.07000:30:17.080 into sodium oxide and 00:30:19.56000:30:19.570 trait goes away and we're left with 00:30:21.66000:30:21.670 silver chloride and I have a little bit 00:30:25.11000:30:25.120 of silver chloride over here let's take 00:30:27.06000:30:27.070 a look we zoom in so there's some silver 00:30:31.68000:30:31.690 chloride and if I shine this ultraviolet 00:30:34.68000:30:34.690 light on it again check out what happens 00:30:37.55000:30:37.560 look at that it turned dark just like 00:30:40.92000:30:40.930 the photochromic glass so basically 00:30:42.93000:30:42.940 we're just dispersing the silver 00:30:44.52000:30:44.530 chloride throughout the glass and that 00:30:46.08000:30:46.090 same process that you just saw is 00:30:47.64000:30:47.650 happening in the glass which causes it 00:30:49.53000:30:49.540 to darken the reason that it becomes 00:30:51.93000:30:51.940 dark is because the silver chloride when 00:30:54.60000:30:54.610 it gets hit with this moderately high 00:30:56.85000:30:56.860 power light it's not quite ultraviolet 00:30:58.68000:30:58.690 that it's pretty close actually converts 00:31:00.96000:31:00.970 into metallic silver and so that dark 00:31:03.03000:31:03.040 color is silver metal as opposed to 00:31:05.46000:31:05.470 silver chloride so if we had a glass 00:31:08.10000:31:08.110 that changed from clear to dark only 00:31:09.81000:31:09.820 once in its whole lifetime it never went 00:31:11.46000:31:11.470 back to clear it wouldn't be that useful 00:31:12.99000:31:13.000 as a pair of sunglasses so we add 00:31:15.18000:31:15.190 another ingredient copper oxide in a 00:31:17.73000:31:17.740 tiny quantity I've written down 0.1 00:31:19.92000:31:19.930 grams but this is actually a 40 X 00:31:21.96000:31:21.970 dilution so we're really only talking 00:31:23.97000:31:23.980 about you know 2 and 1/2 milligrams of 00:31:26.25000:31:26.260 copper oxide for this whole batch of 00:31:27.96000:31:27.970 glass it's considered a dopant because 00:31:31.98000:31:31.990 it's in such small quantity and what 00:31:33.63000:31:33.640 happens here is that it accepts 00:31:35.52000:31:35.530 electrons from the silver chloride so 00:31:38.28000:31:38.290 when you hit the silver chloride with 00:31:39.51000:31:39.520 light it converts to metallic silver and 00:31:41.82000:31:41.830 I think gives up an electron don't quote 00:31:43.86000:31:43.870 me on that 00:31:44.31000:31:44.320 and then the copper oxide accepts that 00:31:46.32000:31:46.330 electron and then pushes it back into 00:31:48.39000:31:48.400 the silver metal causing it to go back 00:31:50.43000:31:50.440 to silver chloride so this is sort of 00:31:52.56000:31:52.570 like a reserve of electrons and copper 00:31:55.86000:31:55.870 oxide has the correct sort of affinity 00:31:58.47000:31:58.480 for this to happen properly I believe 00:32:02.76000:32:02.770 the copper oxide is also chosen because 00:32:04.80000:32:04.810 it works over a large temperature range 00:32:06.60000:32:06.610 so you'll notice that with normal 00:32:09.63000:32:09.640 photochromic even commercially made 00:32:11.07000:32:11.080 photochromic sunglasses at very cold 00:32:13.59000:32:13.600 temperatures they will not become clear 00:32:15.69000:32:15.700 very quickly like if you put it in your 00:32:17.19000:32:17.200 freezer it may take months or weeks or 00:32:19.65000:32:19.660 something to become clear where is it 00:32:21.72000:32:21.730 high temperatures it works pretty well 00:32:22.95000:32:22.960 and the copper oxide is responsible for 00:32:25.92000:32:25.930 reducing that temperature dependence and 00:32:28.43000:32:28.440 then we have sodium nitrate this is an 00:32:32.40000:32:32.410 oxidizing 00:32:33.69000:32:33.700 so when this breaks down in the high 00:32:35.28000:32:35.290 temperatures of the kiln it releases 00:32:37.05000:32:37.060 oxygen gas and this is important because 00:32:39.87000:32:39.880 there could be a fairly strong reducing 00:32:42.63000:32:42.640 environment in there or there could be 00:32:44.70000:32:44.710 and we don't want that to happen because 00:32:46.14000:32:46.150 if there's a reducing environment our 00:32:48.36000:32:48.370 silver chloride or while this is being 00:32:50.73000:32:50.740 formed the silver actually might be 00:32:52.26000:32:52.270 reduced down to metallic silver before 00:32:54.93000:32:54.940 the glass is even done being formed and 00:32:56.91000:32:56.920 you can actually see this in previous 00:32:58.53000:32:58.540 glass batches I had a problem with 00:33:00.30000:33:00.310 little silver droplets being formed in 00:33:02.31000:33:02.320 the crucible obviously this is no good 00:33:04.65000:33:04.660 because we want that silver to stay in 00:33:06.36000:33:06.370 solution for it to give us this property 00:33:11.39000:33:11.400 and then finally I'm not sure if this is 00:33:14.49000:33:14.500 critical or not I started adding sodium 00:33:16.86000:33:16.870 silico fluoride to some of these batches 00:33:19.71000:33:19.720 and the winning batch actually did have 00:33:21.24000:33:21.250 a little bit of sodium silica fluoride 00:33:23.55000:33:23.560 and the idea with this is that it 00:33:25.38000:33:25.390 provides a nucleation center for the 00:33:28.05000:33:28.060 silver chloride to form so the trick 00:33:30.48000:33:30.490 with this heat treatment after making 00:33:32.64000:33:32.650 the glass is that we we have these 00:33:34.68000:33:34.690 silver chloride atoms distributed 00:33:36.63000:33:36.640 throughout the glass it's sort of like a 00:33:38.16000:33:38.170 photograph but it needs to be clear in 00:33:41.28000:33:41.290 its clear state so there can't be too 00:33:42.69000:33:42.700 many of these silver chloride atoms or 00:33:45.21000:33:45.220 parent molecules so what we do is we 00:33:47.28000:33:47.290 heat treat the thing and the silver 00:33:49.17000:33:49.180 chloride we want to aggregate into 00:33:51.09000:33:51.100 bigger chunks and that way they can 00:33:52.98000:33:52.990 actually convert into metallic silver 00:33:54.84000:33:54.850 and give us this great photochromic 00:33:56.43000:33:56.440 property so what we do is add some non 00:34:00.93000:34:00.940 dissolvable stuff these fluorides are 00:34:02.97000:34:02.980 apparently not dissolvable in the glass 00:34:04.71000:34:04.720 they're still clear but there's like 00:34:06.03000:34:06.040 little pellets sort of distributed 00:34:07.62000:34:07.630 throughout the glass and they provide 00:34:09.57000:34:09.580 like a convenient source of condensing 00:34:12.90000:34:12.910 for these silver chloride atoms to start 00:34:14.88000:34:14.890 forming clumps so if you're having 00:34:16.89000:34:16.900 problems getting the silver chloride to 00:34:18.65900:34:18.669 clump you can add this and that will 00:34:20.13000:34:20.140 help out the process if you don't want 00:34:25.38000:34:25.390 to add the fluorides you have another 00:34:26.94000:34:26.950 option to create these nucleation 00:34:28.89000:34:28.900 centers what you can do is just keep 00:34:30.63000:34:30.640 adding so much silver nitrate that 00:34:32.90900:34:32.919 eventually all the silver chloride 00:34:34.83000:34:34.840 that's going to form has formed and then 00:34:37.11000:34:37.120 there's actually excess silver left over 00:34:39.12000:34:39.130 and what will happen is the excess 00:34:41.55000:34:41.560 silver will just hang out in the glass 00:34:43.38000:34:43.390 and so it actually starts out kind of 00:34:45.24000:34:45.250 dark basically the silver provides it 00:34:47.31000:34:47.320 own nucleation centers and this one is 00:34:50.01000:34:50.020 actually photochromic as well the trick 00:34:53.61000:34:53.620 is that it just starts out kind of this 00:34:55.02000:34:55.030 this reddish color because it's actually 00:34:56.85000:34:56.860 silver nanoparticles that are 00:34:58.44000:34:58.450 distributed throughout the glass giving 00:35:00.57000:35:00.580 it this nice color actually so if you 00:35:02.79000:35:02.800 want sunglasses that go from dark to 00:35:04.47000:35:04.480 really dark that's this is the one for 00:35:06.36000:35:06.370 you I forgot to mention that a lot of 00:35:14.10000:35:14.110 these ingredients are volatile at really 00:35:16.38000:35:16.390 high temperatures so we're in the kiln 00:35:18.03000:35:18.040 it you know 1200 degrees see the silver 00:35:21.99000:35:22.000 is not just hanging out in there the 00:35:23.28000:35:23.290 silver is actually evaporating away at 00:35:25.62000:35:25.630 1200 degrees C so to make matters even 00:35:29.73000:35:29.740 more difficult after you've come up with 00:35:31.56000:35:31.570 this you know special formulation if you 00:35:33.93000:35:33.940 were to put all these ingredients into 00:35:35.16000:35:35.170 one of those tiny melting dishes and 00:35:37.14000:35:37.150 left it there overnight at 1200 degrees 00:35:38.79000:35:38.800 C you wouldn't have any silver in there 00:35:41.04000:35:41.050 left what so ever and your glass would 00:35:43.83000:35:43.840 not be photochromic and so it's a really 00:35:47.04000:35:47.050 good balancing act difficult balancing 00:35:49.08000:35:49.090 act between getting the process set up 00:35:51.75000:35:51.760 correctly such that you put in enough 00:35:53.37000:35:53.380 ingredient and then cook it for long 00:35:55.50000:35:55.510 enough such that just the right amount 00:35:57.21000:35:57.220 of ingredient is left over at the end of 00:35:59.28000:35:59.290 this process and it makes it very 00:36:01.50000:36:01.510 difficult if you're using small batches 00:36:03.24000:36:03.250 so if you do this yourself I would 00:36:05.19000:36:05.200 recommend me using bigger melting 00:36:07.62000:36:07.630 containers than I am so I'm making these 00:36:09.45000:36:09.460 like tiny you know we're starting with 00:36:11.88000:36:11.890 20 grams of bori this whole glass ends 00:36:13.95000:36:13.960 up being about 20 grams because all this 00:36:15.75000:36:15.760 carbonate gets burned off so we start 00:36:18.09000:36:18.100 with maybe 30 grams of ingredients or 30 00:36:20.31000:36:20.320 something and we end up with 20 grams of 00:36:22.71000:36:22.720 glass that's really not very much and 00:36:25.59000:36:25.600 the fact that the melting vessel has 00:36:27.66000:36:27.670 like a lot of surface area to it means 00:36:30.66000:36:30.670 that a lot of the silver is burning away 00:36:32.91000:36:32.920 so you're basically talking about making 00:36:34.35000:36:34.360 a soda and then leaving it on the 00:36:36.09000:36:36.100 counter and waiting for it to go flat 00:36:37.95000:36:37.960 but not too flat and then stopping it at 00:36:40.35000:36:40.360 just the right point so that you have 00:36:41.67000:36:41.680 just the right amount of ingredients and 00:36:43.37000:36:43.380 remember that you know the silver is 00:36:45.66000:36:45.670 going to volatilize that a different 00:36:47.13000:36:47.140 rate than the other things are so if 00:36:48.72000:36:48.730 you're trying to control the ratio 00:36:49.92000:36:49.930 between silver and copper for example 00:36:51.45000:36:51.460 and the copper is not volatile or it's 00:36:54.06000:36:54.070 only a little bit volatile and the 00:36:56.10000:36:56.110 silver is really volatile then there's 00:36:57.54000:36:57.550 like this very narrow process window and 00:36:59.58000:36:59.590 so it's it's a lot of tweek 00:37:01.35000:37:01.360 I've made you know I'm probably 50 00:37:02.91000:37:02.920 batches of glass over the last few 00:37:04.41000:37:04.420 months and I found the process to be 00:37:06.69000:37:06.700 kind of fun but also maybe a little 00:37:08.04000:37:08.050 frustrating but I guess that is part of 00:37:10.02000:37:10.030 the fun of it oh one last thing how do 00:37:14.46000:37:14.470 you get these cool colors these are all 00:37:16.68000:37:16.690 special oxides that can be added in 00:37:18.81000:37:18.820 really small quantities and so this is 00:37:20.64000:37:20.650 actually copper oxide so if you put in a 00:37:22.92000:37:22.930 lot more copper oxide than two 00:37:25.08000:37:25.090 milligrams let's say you put in like 00:37:27.09000:37:27.100 actually 0.1 grams of solid of pure 00:37:29.82000:37:29.830 copper oxide you end up with glass that 00:37:31.50000:37:31.510 looks like this this one is chromium 00:37:34.65000:37:34.660 chromium oxide is green and also 00:37:37.80000:37:37.810 interestingly you can control the color 00:37:39.45000:37:39.460 of it based on its oxidation state this 00:37:44.01000:37:44.020 deep blue one is copper oxide when it's 00:37:46.38000:37:46.390 oxidized as hard as you can I think it's 00:37:48.24000:37:48.250 like two-plus maybe and then this is 00:37:50.25000:37:50.260 also copper oxide that is neutral or 00:37:54.03000:37:54.040 even slightly reducing so this might be 00:37:55.80000:37:55.810 like one plus or something and a lot of 00:37:57.93000:37:57.940 these oxides have two colors that you 00:37:59.79000:37:59.800 can get to with different oxidation 00:38:01.35000:38:01.360 states okay well I hope that was helpful 00:38:04.65000:38:04.660 and feel free to ask me any questions if 00:38:06.87000:38:06.880 you get into making glass and I will see 00:38:09.15000:38:09.160 you next time bye
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