Glass engineering - designing and making photochromic glass

today on Applied Science I'm going to talk about designing and creating small batches of glass this is an unusual branch of engineering it's very unlike electrical or mechanical in that there's basically no information available how to get started in the home shop so today I'm going to summarize everything I've learned in the last couple months including reading out of print books and talking to glass experts and show you how to start having fun with this right away okay so let's check out some demos let's take a look at this unusual piece of glass I'm going to shine some light on it from this blue laser pointer that I got from eBay let's see what happens as you can see the glass is actually changing color when I shine light from the laser pointer in there and it's fairly responsive it changes in a few seconds this glass is actually photochromic so it's basically the same kind of glass that is used in sunglasses that change color when you go out into the Sun and some regions ever are a little bit more sensitive than others but you can definitely see what's going on here right let's try this one this one's also photochromic we can also give it a blast of light from this really big ultraviolet flashlight that I have here let's try this one out this is about the same wavelength 405 nanometer as the laser pointer it's just more it's just more of it there's there's more LEDs in here and then just for comparison this is like a modern photochromic lenses that these guys donated to the channel a long time ago just so you can see the performance difference so a modern this is actually a plastic lens and so it's not quite the same chemistry in here but you can just get an idea of of how it works with a modern photochromic lens dies in plastic as opposed to glass and now all of these are actually reversible so if we wait around long enough both the commercial lens and the glasses that I've created are they'll eventually go all the way back to their original state now in the commercial lens this happens in hopefully five to ten minutes in the glasses that I've created it's quite a bit longer could time-lapse this but it's really kind of like an overnight thing for this to translate back to its original clarity pretty cool though there's nothing special about this laser pointer I'll put links to everything as always in the in the description you can go on eBay and just pick up one of these laser pointers okay so that's this is actually making this piece of glass took a long time let me tell you most of the samples that you've seen on this table here were me attempting to make photochromic glass and it's taken a long time because there's a lot of variables involved here and I'm very happy to get this level of performance so this is not anything shocking I mean it's been around since the 1950s or 60s however I'll bet you have not seen a piece of glass that works quite like this one this one is also photochromic but as you can see the fade time is just seconds and so if I go across like this you can see it's there and then it fades this is actually an opal glass and so it it is a piece of glass it's just it's not transparent and it has this really weird property where you can draw on it and then it fades away almost instantly just a few seconds and the top has this weird kind of crystalline thing going on but it also works about the same way almost unfortunately this was a batch of glass that I made just by throwing a bunch of leftovers together in a pot so the point the formula for this one's unfortunately lost the time forever but the point is that I want to get everyone into hacking glass because with you know as many people hacking on electronics and mechanics if they were all hacking on making glass we would have all kinds of weird stuff by now so let's start talking about how to do this when I first got started with this project I thought what I would do is get a mold a glass mold dump all the ingredients in there with a mold release heat it up cool it and then pull out my finished piece of glass however it can never work that way unfortunately and the reason is that the glass batch when it's being formed like going from a mixture of powders into a finished piece of glass is extremely reactive and all of the mold releases that you can put in here will actually get sucked up into the glass batch and then you won't have a mold release anymore there's only one material on earth that won't stick to melting glass or forming glass and that's platinum and so they actually make tiny little platinum crucibles for doing laboratory glass analysis but that's a little expensive and apparently from what I've heard even then the glass doesn't just fall out I mean it still sticks in there and so if you're hoping to make like a nice you know good-looking puck of glass it's not gonna work forming it in a mold like this so I'll just cover that the mold releases quickly if you do make a custom blend of glass and then you want to form it into an interesting shape then you can use these conventional mold releases and most of these things came from like an art supply house for glass artists to popular kinds of mold release are this primo primer and this is a powder in here that you mix with water and it ends up making this fun purple solution and the purple is actually a useful thing when you're brushing it on your mold you can tell the spots that you haven't covered because they aren't purple so that's the point of that and then I also tried this really expensive boron nitride mold release this is actually really great stuff it's also fifty dollars it can and it works really well but again if you're making glass the temperatures are really high and the glass is very reactive and it will actually suck the mold release into the glass batch and that's actually what's happened here so this was a mold that I coated with that boron nitride spray and I put my ingredients in here and what happened this brown color is actually the boron nitride that's been incorporated into the glass and then after the glass was done eating away all of my mold release it proceeded to stick itself permanently to the mold which is alumina so what happened here is I basically just glazed the mold I started with this unglazed piece of alumina and now the glass is permanently fused in there so the way to do it is to get a melting dish and I'll put links again to all this stuff these are these you can actually buy these on Amazon they're a little expensive on Amazon if you get these imported you know from a Chinese seller on eBay it's just like a buck or two I mean it's no big deal and you can take these up to very high temperature and what you want to do is put your glass batch in here heat it up and then pour it out onto something else but we'll get into the details later also I should point out that you might have heard of float glass so commercially if you want to make like a big sheet of glass and make sure that it's really flat what can you do you don't want to put it through rollers because the rollers you know might Mar the surface or you have to adjust them to make them really parallel so the way the glass is made commercially is a giant vat of molten tin and they pour the molten glass on top of the Bolton tin and because gravity is makes things flat at the small scale here you're guaranteed that everything will be flat and uniform because you're dealing with liquids on the surface of the lake right it's going to be flat there's a couple of interesting crowded of course inside here I've got some tin I bought tin pellets on eBay and put them in my crucible here and melted it and then put some glass on top and you can see it it kind of almost worked but there's a couple of interesting problems one the tin oxidizes if you just heat it up in air so commercially what they do is have a giant furnace full of hydrogen gas where this liquid tin is hanging out and the hydrogen gas is very reducing it basically prevents oxygen from from being in there because if any oxygen got in it would react with the hydrogen so needless to say this is getting to be kind of difficult to do in the home shop having a molten tin with hydrogen gas and everything and then another interesting problem if you're making photochromic glass for example you can't do it in the float glass process because this glass is very sensitive to the environment it's in and it really doesn't like hanging out in a hot hydrogen environment because it actually prevents the glass from being photochromic so this can only be formed in crucibles or in oxidizing environments you can't use the float glass process for this so originally when I was having this problem with the glass sticking to the the molds and I was wondering what to do I thought well maybe I'll try this liquid metal idea since how could it stick to liquid metal and I would recommend not bothering with this at all as it turns out if you want to make a flat piece of glass in the home shaf there's easier ways to do it just forget the tin it's it's actually not that helpful if you're in a bind and you can't find or afford these aluminum melting dishes it's also possible to use porcelain so if you go to the store and buy you know dishware just plain old porcelain destroyed this can be okay the temperature that this can sustain is just barely high enough to do some glass experiments and we'll get about you know we can talk about making the glass melt at low temperature so that you can use porcelain melting stuff the one thing you have to be careful about is that if you buy dishware from the store it's already glazed right so there's already glass inside here on top of the porcelain you can feel the difference like if you touch this part of it it's typically not glazed so that's the raw porcelain and then inside it's already covered with glass so if you're making a glass batch and you pour all your ingredients in here it's going to be mixed along with whatever glaze the manufacturer already used whereas if you if you go with one of these unglazed melting dishes this is really raw there's there's nothing that this is going to contribute to your glass batch shirts it's the minimal amount okay so you've got your aluminum melting dish or your porcelain demitasse and you're ready to put it in the kiln to melt all the stuff down so let's talk about kiln selection first gas versus electric in this tabletop small scale size there are no commercial gas kilns so you'd have to make one but that's you know not the end of the world there's a couple other considerations though - you want your kiln to have really good temperature control like plus/minus 10 20 degrees C because a lot of making unusual parts of unusual kinds of glass involve heat treatment and annealing and you really do need good temperature control to do this so you know really fine temperature control with a gas kiln is it more difficult you probably need to like throttle the gas down not just turn it on and off to get good temperature control but the last consideration and sort of the most difficult one to get around is the atmosphere inside the kiln remember I was saying that having hydrogen atmosphere is no good for photochromic glass so they actually chemically hurt the glass and prevent it from being photochromic if you have a gas-fired kiln the exhaust from your flame is actually reducing there's probably quite a lot of carbon monoxide in there and at these temperatures that carbon monoxide will find oxygen molecules and react with it to make carbon dioxide and it's so reducing at these high temperatures that it will actually pull oxygen out of the glass and prevent it from being photochromic so I don't know I think commercially you could probably get around this by having like a really big crucible inside your gas-fired kiln and it's only the surface layer that's affected by the reducing atmosphere and a gas-fired kiln the trouble is if you're using small little melting dishes like this the amount of surface area appears high enough where if you've only got you know 100 grams of glass in here it's basically all going to be affected by the atmosphere in the kiln so using an electric kiln is very nice because temperature control is much easier and if you open the lid to the kiln you're guaranteed to have atmospheric air inside there later on you'll see there's so many variables involved with making a piece of glass that eliminating one more variable of having this unknown atmosphere from a flame in your kiln is another thing especially if you're turning the flame on and off to control the temperature now you're controlling also the oxygen level because the flame is on and off and so then there's more or less oxygen I would recommend definitely going with an electric this particular kiln here is called a muffle kiln and it's built kind of funny it almost seems like a DIY project itself it's basically just this helmet shaped thing and they can see the heating elements inside there and you can put it down on any surface you want and sort of turn that into a kiln this is the Paragon quickfire I bought this a long time ago it's not sponsored of course this is about three hundred dollars new I think and it's actually a really good solution the heating elements are rated to go up to about 1050 degrees C but I've pushed it to 1150 no problem one consideration is that it just comes with a switch so the the original temperature control is a switch that you turn on and off yourself and a analog temperature gauge here to tell you how hot it is and that's not going to work for doing a glassy treatment or annealing so what I did is I added this little pig controller here and you can set the temperature and it's actually amazingly good at reaching a temperature and holding it within just a few degrees even the reason that this kiln is limited to maybe 1150 C or even 1250 if you really really push it is because the heating elements themselves are made of nickel iron right nichrome and eventually it melts so it's a pretty hard limit on how hot you can get it because your heating elements eventually get so hot they melt so that that really does put a cap on things and unfortunately most silica glass patches have a rated like melting or forming temperature of like 14 or 1500 degrees C which is much too hot you'd never get your night chrome furnace that hot so what do you do well there are actually special electric furnaces that have heating elements that are not made of nichrome so the next level up from nichrome is silicon carbide is actually conductive and it melts at a higher temperature so they make heating elements out of that and then the top of the line is molybdenum disulphide very unusual material that's a blend of molybdenum and silica and they make these very very expensive small heating elements out of this material and you can get a kill on an electric kiln that goes up to fifteen or sixteen hundred degrees C the downside is that these kilns are really expensive even you know cheap import models on eBay sell for like two or three thousand dollars so you know it's in the context of this video it's really just kind of out of reach I wouldn't worry about it the nice thing is that you can make glass formulations that just don't require that kind of temperature so there's a lots and lots of experimentation you can do without father and with any of that and that's what we're going to talk about in this video this kiln originally came with its own shelf like its own bottom and you can see what happened here now remember I said that glass is very reactive so if you spill a little bit of glass batch on the Shelf here and then heated up to high temperatures it's actually dissolving away the material of the kiln itself so you have to protect the kiln and everything in there from your from your glass even spilling it is actually a very damaging like corrosive kind of event so luckily this this material is not super expensive and the nice thing about these muffle furnaces where you sort of pick the whole furnace up is that you can just have like a new bottom every month or whenever you need it so you can buy these fire bricks that are very lightweight and can take very high temperatures and are also insulating so I'll put links to all this if you search for fire brick be careful because some fire bricks are rated for high temperature but they aren't really insulating like it can withstand fire of it it's gonna get hot on the other side whereas it brick like this it could be you know 1,400 degrees C on this side and you could put your hand on this side and it would be no problem so to repair this kiln but I do this I just put two of these standard sized insulating fire bricks here and that's now my kiln floor another thing you can do to try to promote the life of your kiln floor is to cover it with this special kiln paper so they sell this stuff at the art supply stores and watch watch how it works pretty cool it's paper that doesn't really burn and so if you put glass on top of here this axe is sort of like a buffer layer and this will eventually become completely white ash and the glass won't be able to stick to the kiln floor because there's this layer of ash in between so pretty handy stuff just keep in mind though that if you pour your glass batch like if there's powders on here that are gonna form a glass they will dissolve the paper and the ash and everything else like we mentioned and eventually get all the way through so this is sort of a low-level way to protect yourself from spills you can see in my in my kiln here there's all kinds of remnants of ash here since I've been putting kiln papers on here to try to protect the top not 100% though because you can still see little errors here and there oh also you can use sort of a trivet so what will happen is the glass is very viscous and sticky and so if you've got your melting dish like this eventually you'll get some running down the side here it'll dribble down and if it's just sitting on top even with the kiln papers it'll eventually make a huge mess and destroy your kiln floor so you can put like a porcelain or alumina tray here so that when you put this down the drip is at least caught by that you keep the kiln floor living a little bit longer so we talked about making your glass batch in an alumina melting dish like this and then pouring it out on to a surface there's actually a really great material for doing this and that's graphite so if you go on eBay or Amazon you'll find there is these graphite Casting molds mostly for metal actually they weren't thinking that you'd use this for glass but you can and what I found to work really well is to get a mold of about this size and put it down like that you can use sandpaper to get the surface really flat and then use like a paper towel to polish it and then when you're getting ready to pour your glass what you do is you the surface up with a torch till you know it's maybe a few hundred degrees C or maybe even five hundred and then obviously there's gonna be hot open the kiln up and take your glass and pour it out onto the surface and the nice thing is that the graphite will not stick to your glass hardly at all I mean it's a really slippery surface what I found out doesn't work don't do this don't take the whole thing and put it in your kiln and then close the lid and heat the whole thing up to kill them temperatures the the graphite will survive but what will happen is the glass will rip off the top layer and it again incorporate the graphite into the glass because it's so reactive so that doesn't work okay so we've talked about the melting dish the kiln the mold release and everything what do we actually put in the dish to make this glass this is where things get really weird so if you search for patents about you know how to make weird kinds of glasses let's say photochromic glasses you'll find lots and lots of very detailed glass analyses right so you'll typically see let's say you find a glass analysis it's 50% silicon dioxide you know 40% boron trioxide 10% sodium oxide great I'll just get you know 50 grams of silica 40 grams of or 8 and 10 grams of sodium oxide and mix it all together and make a glass right not even close the ingredients that are that go into the glass batch do not have a whole lot to do with what comes out the other end and this may seem very strange but there's a really great analogy and that's in cooking so if you analyze the piece of cooked bread you would say it's you know 20 percent gluten 20 percent water whatever it is but if you're explaining how to make a blow for Fred to someone you wouldn't use those terms you would say start with flour and water and it's actually the process of making the bread that develops it into gluten and all the other finished products and that's that's exactly what's happening with the glass one trick with making these glass batches is that the temperatures are so high that almost any carbon is going to go away it's going to react with oxygen and leave the glass batch entirely so if we for example put in lithium carbonate when we heat this up to you know 1200 degrees C the co 3 is going to go away and the oxygen is gonna there are some of the remaining oxygen is going to react with the lithium and we'll be left with lithium oxide in the glass so and then you might say well why not just start with lithium oxide the problem is that lithium oxide is really reactive and so if you put that in the glass batch it's very possible that as the thing is heating up all that lithium oxide is also going to go away before it has a chance to be incorporated into the glass batch so choosing ingredients to make a glass sort of requires you to find an ingredient that has a melting point and a stability that is compatible with all the other materials in glass luckily a lot of this work has already been done so if you sit down and you know you want to put lithium in your glass you pretty much use lithium carbonate there might be a few other chemicals that work too but pretty much it's always lithium carbonate and also for example if you want to add sodium to your glass pretty much using sodium carbonate is the way to go okay unfortunately there's not like a master table or anything that I have found that lists all the possible things you can put in I mean there's literally hundreds it goes on and on but to make sort of more normal kinds of glass it is pretty well figured out and I'll put as many links as I can in the description to help you out when you're just starting out and making a relatively simple kind of glass just plain old clear glass I would recommend is doing twenty grams of silicon dioxide 20 grams of sodium carbonate and 20 grams of boric acid and this will make you a borosilicate glass you've probably heard that term before it's the same kind of glass that's used in glassware and cooking dishes and all this kind of thing one benefit of borosilicate glass is that it is less sensitive to temperature fluctuation right like you don't want your glass to crack if you're heating up a test tube or something like that and similarly if you're making glass on your own you actually don't want it to be very temperature sensitive because you're gonna have to cool your piece of glass down from kiln temperatures all the way to room temperature and annealing is the process where you pick a temperature and hang there for a while to let the glass relax and sort of all the stresses dissipate and it typically takes hours for this to happen but having borosilicate glass you still have to anneal it but it's less sensitive than a non borosilicate glass or something that's more sensitive to temperature fluctuation mixing up all the powders is pretty important and it's something that I haven't spent a huge amount of time on but I probably should what I typically do is just have the container on the scale put all the powders in it and then sometimes I'll add these to brass balls and put the container lid on and shake it around and the balls will help sort of stir up the powder and actually kind of crush some of the crystals a little bit to mix it up in reality this could be a lot better any what you really want to do is put it in a rock tumbler and run it for a day or an hour or something like that and that will make sure that the powders are really really well mixed together and this is important because like we were talking about the glass batch doesn't just sort of all melt together it's actually a chemical reaction that's happening in there so you really want the powders to be in really really well mixed intimate contact with each other so that the chemical reactions can proceed as smoothly as possible if you've got a clump of something off in one corner of the crucible it's possible it will eventually melt and make a glass for you but it may not have the properties that you want because it didn't properly react with all the other ingredients and again think of a loaf of bread right like if you have a little chunk of unmixed flour or something in one corner of the pan yeah you'll still end up with a loaf of bread or something but it's not gonna be as good and funny enough the analogies with cooking continue this is actually a good ingredient to put in your glass just plain old table salt will add sodium and chloride and both of those are actually important in making photochromic glasses and so it's no joke that you know if your soup isn't very good what do you do you know you put in a pinch of salt same can be true of your batch of glass the main components of the glass are not super sensitive to variations in ratio so for example if your glass is 1/2 silica and about half bori you know getting it to be 4951 isn't going to make any difference but when you're making them glasses that are photochromic or have like a very sensitive chemical aspect to them some of the ingredients are very sensitive and the quantities are just absolutely tiny so for example in the photochromic glass this copper oxide needs to be added about point oh eight percent I think and so measuring out such a teeny amount even with a balance that's capable of measuring milligrams is very challenging so what you do is you dilute the sensitive ingredient in one of the base ingredients so for example for this borate glass I'm using boric acid as like the main batch component and so what I would do is take half a gram of copper oxide and mix it with 20 grams of borate and so I'll have this very dilute sort of copper oxide powder and then you can measure this out with also still pretty good precision but not quite the precision that you need to measure the oxide by itself let's finish up by talking about the actual chemical ingredients that go into this photochromic glass sort of as an example and I'll try to describe and generalize what these ingredients do so this winning combination that I've got here this photochromic glass has this recipe it's 22 B as you can see I spent a long time tweaking different components of the recipe there are a lot of variables involved here not only is the ratio of ingredients important but also the speed at which you bring them up to the melting temperature in the kiln and then how long you hold it at that temperature and then when you pour it out of the kiln you let it cool down to room temperature and then bring it back up to a forming temperature to actually create this photochromic property and then of course that has a time and temperature associated with it as well and the atmosphere and the kiln during the melt process and then the atmosphere during the heat treat process and it just goes on and on so I'm not claiming that this is tweaked it down to perfection in fact far from it this will just give you an idea of what's going on and sort of the the challenges that you'll encounter if you end up doing this I should also point out that a lot of the patents around photochromic glass talk about a lot of these times and temperatures but they'll say things like the heat treatment may be conducted between 500 and 700 degrees C for between ten minutes and two hours now what will actually happen is that the heat treatment only works between 600 and 600 twenty degrees and it must be between 30 minutes and 40 minutes but of course they want the patent to be as broad as possible and if there's some weird way you can make it work outside those parameters then fine but they're definitely not describing the easiest way to make it they're describing all the possible ways to make it and so that's kind of another problem with the patent system is that it's you write them to be overly broad but anyway okay let's get down to business here with the chemicals this winning combination is a borate glass there's actually no silica in it whatsoever so it's not borosilicate it's just for Oh borate glass so we've got 20 grams of boric acid this will contribute b203 or borate in the final glass and this is kind of the backbone of the whole system then we have 2.2 grams of aluminum hydroxide now remember the hydrogen is going to go away at these high temperatures and we're going to be left with al 2 O 3 so alumina which is dispersed among the mixture and the function of alumina is just to stabilize the glass structure we don't want it to diva trophy which means convert from a glass into a crystalline structure and this helps with that this ingredient also calls for calcium carbonate which again the carbonate is going to go away and this is going to become calcium calcium oxide in the final glass and this is also a stabilizer that makes the glass less dissolvable like less prone to being broken down by the environment I know that sounds silly for a glass that we only care about you know I just want this to work in the lab I don't care if this survives for years and years but again I was following a recipe and I got this thing locked in and I couldn't change this variable easily because I was too busy changing other variables basically then we have 0.4 grams or 0.3 grams in the winning mixture of silver nitrate this is actually the same chemical that works in old-fashioned black-and-white photography and it's actually the same mechanism inside the photochromic glass so what happens is we mix silver nitrate with sodium chloride in this glass mixture and then as it's reacting as the glass is being formed these things trade places and we end up with silver chloride and sodium nitrate and the sodium nitrate gets burned down into sodium oxide and trait goes away and we're left with silver chloride and I have a little bit of silver chloride over here let's take a look we zoom in so there's some silver chloride and if I shine this ultraviolet light on it again check out what happens look at that it turned dark just like the photochromic glass so basically we're just dispersing the silver chloride throughout the glass and that same process that you just saw is happening in the glass which causes it to darken the reason that it becomes dark is because the silver chloride when it gets hit with this moderately high power light it's not quite ultraviolet that it's pretty close actually converts into metallic silver and so that dark color is silver metal as opposed to silver chloride so if we had a glass that changed from clear to dark only once in its whole lifetime it never went back to clear it wouldn't be that useful as a pair of sunglasses so we add another ingredient copper oxide in a tiny quantity I've written down 0.1 grams but this is actually a 40 X dilution so we're really only talking about you know 2 and 1/2 milligrams of copper oxide for this whole batch of glass it's considered a dopant because it's in such small quantity and what happens here is that it accepts electrons from the silver chloride so when you hit the silver chloride with light it converts to metallic silver and I think gives up an electron don't quote me on that and then the copper oxide accepts that electron and then pushes it back into the silver metal causing it to go back to silver chloride so this is sort of like a reserve of electrons and copper oxide has the correct sort of affinity for this to happen properly I believe the copper oxide is also chosen because it works over a large temperature range so you'll notice that with normal photochromic even commercially made photochromic sunglasses at very cold temperatures they will not become clear very quickly like if you put it in your freezer it may take months or weeks or something to become clear where is it high temperatures it works pretty well and the copper oxide is responsible for reducing that temperature dependence and then we have sodium nitrate this is an oxidizing so when this breaks down in the high temperatures of the kiln it releases oxygen gas and this is important because there could be a fairly strong reducing environment in there or there could be and we don't want that to happen because if there's a reducing environment our silver chloride or while this is being formed the silver actually might be reduced down to metallic silver before the glass is even done being formed and you can actually see this in previous glass batches I had a problem with little silver droplets being formed in the crucible obviously this is no good because we want that silver to stay in solution for it to give us this property and then finally I'm not sure if this is critical or not I started adding sodium silico fluoride to some of these batches and the winning batch actually did have a little bit of sodium silica fluoride and the idea with this is that it provides a nucleation center for the silver chloride to form so the trick with this heat treatment after making the glass is that we we have these silver chloride atoms distributed throughout the glass it's sort of like a photograph but it needs to be clear in its clear state so there can't be too many of these silver chloride atoms or parent molecules so what we do is we heat treat the thing and the silver chloride we want to aggregate into bigger chunks and that way they can actually convert into metallic silver and give us this great photochromic property so what we do is add some non dissolvable stuff these fluorides are apparently not dissolvable in the glass they're still clear but there's like little pellets sort of distributed throughout the glass and they provide like a convenient source of condensing for these silver chloride atoms to start forming clumps so if you're having problems getting the silver chloride to clump you can add this and that will help out the process if you don't want to add the fluorides you have another option to create these nucleation centers what you can do is just keep adding so much silver nitrate that eventually all the silver chloride that's going to form has formed and then there's actually excess silver left over and what will happen is the excess silver will just hang out in the glass and so it actually starts out kind of dark basically the silver provides it own nucleation centers and this one is actually photochromic as well the trick is that it just starts out kind of this this reddish color because it's actually silver nanoparticles that are distributed throughout the glass giving it this nice color actually so if you want sunglasses that go from dark to really dark that's this is the one for you I forgot to mention that a lot of these ingredients are volatile at really high temperatures so we're in the kiln it you know 1200 degrees see the silver is not just hanging out in there the silver is actually evaporating away at 1200 degrees C so to make matters even more difficult after you've come up with this you know special formulation if you were to put all these ingredients into one of those tiny melting dishes and left it there overnight at 1200 degrees C you wouldn't have any silver in there left what so ever and your glass would not be photochromic and so it's a really good balancing act difficult balancing act between getting the process set up correctly such that you put in enough ingredient and then cook it for long enough such that just the right amount of ingredient is left over at the end of this process and it makes it very difficult if you're using small batches so if you do this yourself I would recommend me using bigger melting containers than I am so I'm making these like tiny you know we're starting with 20 grams of bori this whole glass ends up being about 20 grams because all this carbonate gets burned off so we start with maybe 30 grams of ingredients or 30 something and we end up with 20 grams of glass that's really not very much and the fact that the melting vessel has like a lot of surface area to it means that a lot of the silver is burning away so you're basically talking about making a soda and then leaving it on the counter and waiting for it to go flat but not too flat and then stopping it at just the right point so that you have just the right amount of ingredients and remember that you know the silver is going to volatilize that a different rate than the other things are so if you're trying to control the ratio between silver and copper for example and the copper is not volatile or it's only a little bit volatile and the silver is really volatile then there's like this very narrow process window and so it's it's a lot of tweek I've made you know I'm probably 50 batches of glass over the last few months and I found the process to be kind of fun but also maybe a little frustrating but I guess that is part of the fun of it oh one last thing how do you get these cool colors these are all special oxides that can be added in really small quantities and so this is actually copper oxide so if you put in a lot more copper oxide than two milligrams let's say you put in like actually 0.1 grams of solid of pure copper oxide you end up with glass that looks like this this one is chromium chromium oxide is green and also interestingly you can control the color of it based on its oxidation state this deep blue one is copper oxide when it's oxidized as hard as you can I think it's like two-plus maybe and then this is also copper oxide that is neutral or even slightly reducing so this might be like one plus or something and a lot of these oxides have two colors that you can get to with different oxidation states okay well I hope that was helpful and feel free to ask me any questions if you get into making glass and I will see you next time bye

Channel: Applied Science

Views: 490,042

Keywords: glass, engineering, glass making, melting, glass batch, photochromic, applied science, ben krasnow, krasnow, phototropic, how to make glass, diy, home, borate, silicate, borosilicate

Id: mUcUy7SqdS0

Length: 38min 17sec (2297 seconds)

Published: Sat Nov 25 2017