Can you GROW an Opal?

of all of the gemstones opal is easily my favorite it stands unique amongst the gems as it really isn't a class of its own it's not a crystalline mineral like diamond or ruby it's made of silica but it's not crystalline like quartz or glass like obsidian and it looks completely spectacular and nothing like the other gems opal exhibits what's called play of color which means that it literally changes color as you look at it from different angles but not all at once different spots in the gem will change color at different times and different amounts than other spots even those right next to each other opal comes in a few flavors but the most prized are black opal as the dark background makes the flashes of color much easier to see they're also graded based on how nice that play of color and pattern is some of the nicest opals can sell for a couple of grand per carat and be quite large racking up a pretty price tag there are several places opel can be found around the world and the opal will look different depending on the mine it comes from because each formed under slightly different conditions and with different stuff around it while it forms the opal from virgin valley nevada for example forms in and amongst petrified wood and looks particularly cool but the highest value opal usually comes from places like cooper petty in australia where opal's worth many thousands of dollars can be mined if you haven't seen it already smarter every day has a fantastic video where he visited cooper petty if you want to see how the real thing is collected and the process is pretty wild it involves digging big bore holes in the desert then climbing down them to try and find the opal layer but we're not here to see how real opal is mined no today we're going to be talking about how we make it ourself and it's both surprisingly easy and surprisingly difficult at the same time synthetic opal can look just as amazing as the real thing and even be very difficult to tell apart but sells for a fraction of the price because it's quite cheap to make i've made several opals and growing them is a fairly straightforward process but the fine details are what makes the difference between a synthetic that's so convincing it's impossible to tell from the real thing and one that is a clear fake the latter being easier and faster to make but still stunning in its own right in my opinion i find a lot of the synthetics often look much better than most low-grade real opals which i find very interesting though of course that's just my personal taste i just wish i could find a nice big chunk of raw synthetic to add to my growing opal collection i've become a little bit obsessed with making gemstones synthetically as i just love the idea of making something that people put so much value on from materials that cost pennies at the end of the day they're all just shiny rocks but some have commercial value outside of their beauty ruby sapphire and diamond are incredibly tough materials and so making them industrially is useful as they can be used to make cutting and grinding implements there's a few channels that have made rubies already but i'm currently working with an engineer friend to make some sapphires that are a little bit larger and hopefully in higher quality maybe even laser quality if i'm lucky diamond is a tough nut to crack but i may have actually already done it and i was about to get the results analyzed before the rona hit but now getting analysis done is basically impossible so opal was next on the list and was the first to see real success which is why we're talking about it today to understand how we're going to go about this we first need to understand the structure of opal unlike a traditional gem which is a solid chunk of material through and through opal is actually composed of tiny spherical nanoparticles of silica which are all stacked together in a proper crystal the structure is made up of individual atoms stacked together in a specific pattern whereas with opal the individual particles are just amorphous globs of atoms but together form a sort of pseudo-crystal so to make an opal from scratch all we need to do is make silicon nanoparticles of the right size and stack them together but that's easier said than done as the stacking needs to be just right for this to work potch opal which is the stone found around precious opal is made of the same material but just looks white because the particles aren't aligned properly so even if we make the particles we won't get any color if we can't stack them correctly but before we talk about how to stack the particles and why stacking them one way makes them colorful let's actually make some of the particles this process is rather stinky and the chemicals aren't super pleasant so i took a trip across town to visit my friend nile red his lab has a pair of awesome fume hoods and he's got all the tools i'll need for this so i was super grateful that he let me come and film so huge thanks to him the reaction itself is actually pretty simple and the materials aren't overly expensive though one of them is rather hard to find for this i'll need water and ethanol to act as a solvent for the reaction ammonia which will act as a catalyst and finally i need a silica precursor and the best choice for that is something called t-e-o-s or tetraethyl orthosilicate commercially it isn't expensive and a big bottle costs maybe a hundred dollars but not many places sell it especially to individuals i happen to get lucky and find a seller on ebay that randomly had a listing for some and picked up about 30 milliliters but that seller is long gone it does occasionally pop up for sale but you kind of have to get lucky or bite the bullet and get a sigma account but that's it for chemicals i'll be using something called the stuber process which allows you to make silicon nanoparticles of uniform and consistent sizes and what's really cool is that it's very easy to set the size of the particles by simply changing the amount of ethanol that you use i've linked to a great paper below that gives exact details on this process for opal we want particles in the range of 200 to 350 nanometers the larger they are the more red the final opal will be i ended up doing several runs to make particles of different sizes and we'll look at those results in a minute as they really change the way the final opal looks by a fair bit for the reaction i set up a water bath on a hot plate and then set a round bottom flask inside it a thermometer is going to be used to monitor the temperature of the water bath and it needs to be held at 60 degrees celsius for the entire reaction i used a torch to flatten the end of a glass stir rod into a stirring head and then mounted that into an overhead mixer which will be used to stir the reaction i also dropped a paper clip into the water bath so i can stir the water and keep the temperature even to the flask i add 50 milliliters of 94 ethanol 3 milliliters of water and 8 milliliters of a 25 ammonia solution this is allowed to stir for a few minutes to make sure it's all at 60 degrees celsius before starting then when everything is ready six milliliters of teos is added to the reaction and the flask is loosely covered with a bit of parafilm to try and keep some of the vapors in this is why the fume hood is needed otherwise the ammonia would stink up the whole room very quickly and the tos vapor isn't particularly great for you as you can react in your lungs and coat them in silica which i have been told isn't particularly healthy but other than that you just kind of leave it alone for two hours for it to do its thing as soon as the teos is added the solution quickly starts to become opalescent and eventually turns an opaque white but after that it just looks the same for the rest of the two hours the way this reaction works is the ammonia causes the tos to lose ethyl groups as ethanol and linked together this forms a web of chemical bonds as it goes on this process starts randomly many times at the beginning which makes tons of super tiny particles which act as nucleation sites as it goes on the initially formed particles have more and more surface area to react with so eventually become the main place where this reaction happens the stirring keeps the particles separate and the limited amount of tos stops the reaction once they're the right size the amount of ethanol we use makes the reaction more or less concentrated which changes how many particles form initially more particles mean the teos gets spread out thinner over a larger number of particles making them smaller as it runs out faster the recipe i just gave that uses 50 milliliters of ethanol will make particles that are about 290 nanometers wide and make green particles they aren't actually green as you can see but you'll understand why i call them that in a second to make red i used 46 milliliters and for blue i used 60 milliliters now why do i call these red green or blue well let's take a sample of each and pour it into a petri dish and allow it to fully dry out what's left is either a whitish film or little blobs but when i tip the dish and it catches the light you can see that it flashes a distinct color the red one flashes red green flashes green and blue does blue but the bulk solution and the particles themselves are just white so what's going on here well this is an example of two phenomena structural color and brag diffraction when the particles are allowed to dry out like this they end up extremely tightly packed and are an ideal example of bragged fraction brag diffraction happens when the wavelength of light hitting a material is very close to the gaps between the particles that the material is made of normally brag diffraction is used for x-ray crystallography because the spacing between atoms in a crystal happens to be very close to the wavelength of x-rays but these nanoparticles happen to have gaps that are very close to that of the wavelength of visible light the bigger the particles the bigger the gap and so the longer the wavelength will interact with hence why bigger particles make redder materials the reason why you see flashes of a specific color is because of light's wave-like properties and how it bounces off the particles at specific angles the gap between the particles is an integer multiple of a specific wavelength of light some of that light will bounce off the first layer of particles while some will travel a bit further into the material and bounce off the next layer under this perfect condition of particle size and angle these two waves line up so they constructively interfere and look much brighter whereas all the other wavelengths that aren't an integer multiple don't quite add up perfectly and so destructively interfere and look dimmer to us this appears as one bright color reflecting off the material but the angle is important as things only line up perfectly at specific angles at slightly different angles the gaps will be a little bit wider or thinner so different wavelengths shine brightly and at really different angles it'll just look white as none of the gaps or angles is correct for any particular wavelengths and so it just kind of bounces off randomly but if all of these particles look a specific color when dried out like this how do we get it to look like opal and why does opal look colorful even though the particle size is fairly uniform well the answer comes down to how the particles actually pack when we dry them out like this they mostly go to their maximum packing density so we get the kind of idealized case but if we allow the particles to very slowly settle out of solution or use something like a centrifuge to crash them out they won't pack quite so densely and certainly not nearly as evenly so some areas will have slightly different spacing than others and so will interact with different wavelengths of light in fact in both cases either settling out slowly or using a centrifuge the particles end up packing into a sort of pseudo-crystal pattern where small areas of particles form distinctly different grains as if they were individual crystals these grains will each have distinct spacing and be sitting at random orientations relative to the other grains which is how we get that play of color i wanted to actually see the particles i made and how they pack so i reached out to ben over at applied science as i said the particles are only a few nanometers wide so are far too tiny to see with a regular microscope ben was kind enough to examine some of the red particles with his scanning electron microscope so we could actually see them i sent the red ones specifically because they're the largest and should be the easiest to see the image is a little bit fuzzy because of the resolution of his scope but you can still clearly see the particles packed together in their nice orderly structure and that they're nice and round he also included some images of a commercial cd taken at the same scale so i can use it as a measuring stick the center to center distance between the ridges on the cd track are 1.6 micrometers wide so using that as a scale bar to calibrate the opal images you can see that the particles are about 350 nanometers wide which is exactly what i was expecting he also took some measurements with his spectrometer and sure enough the red particles have a sharp reflection peak at 650 nanometers which is bright red but at slightly different angles the peak wavelength shifted which is also exactly what you would expect with brag diffraction as it's highly angle-dependent and why you get that play of color in opal as you tip it at different angles but i did say that this is an example of two phenomena we talked about brag diffraction but the other is structural color as we saw the color of these materials comes not from a material property the way say a dye or mineral gets its color but instead from the nanostructure of the material turns out lots of other things have the same property lots of other nanoparticles for example even of other shapes can do this as long as they're all uniform size but even biological things can do this certain viruses like the tobacco mosaic virus can be quote unquote crystallized and forms a distinct opaly pattern there's also some bacteria that are just the right size and have the ability to orient themselves such that they look iridescent and colorful even though they lack any pigments and of course there's more macro examples like this blue morpho butterfly wing which looks blue not because of a pigment but because of the nanostructures on its scales you can even see the same thing in slices of meat occasionally where the cells that make up the muscle tissue all happen to line up just right and give an opely sheen these embossed holograms which we looked at in my last video actually work on a similar principle they aren't colorful because of a dye but because of a nano structure on the surface of the plastic and because of that their pattern can be transferred to things like chocolate and make it colorful too there's also another material i want to mention quickly called inverse opal it's made in a very similar way but instead of silica particles they use polystyrene particles instead once the basic opal shape is made the voids between the particles is filled with the material you actually care about and then the polystyrene can be dissolved away leaving hollow voids behind there is way more research about making inverse opal than regular opal as it actually has uses beyond is a pretty rock like energy storage and electrodes and that sort of thing but it too has fun optical properties for a lot of the same reasons as regular opal and is usually brightly colored okay without out of the way back to making some gemstones we've got our bulk solutions now let's make some actual opal with them the fastest way to do this is with a centrifuge it still takes time but not the weeks or months it would take to let things settle out naturally so i loaded some of the solution into a few tubes and spun it down for an hour or two at 3500 rpm eventually all the particles had settled into a very firm pellet on the bottom i simply poured off the upper liquid and was left with essentially just a hunk of pre-opal and let's just take a moment to appreciate how freaking gorgeous this is remember all this color comes from the nanostructure and not the color of the particles themselves this first batch used green particles and you can see it looks distinctly reddish pink with streaks of other colors it's hard to see on camera but at the right angle it does have streaks and flashes of green as well the next batch used blue particles and this time the main color you see is green but again at the right angles you see blue and lots of reds when i tried doing this with red particles though you see almost nothing it basically just looked like a white chunk if we look at a small piece of the centrifuged opal under a microscope we can see the grain pattern more clearly as i move the light around you can see different areas light up and flash different colors and if i catch it at just the right angle you can see some of that tiger striping of the layers of particles even some of the original dried stuff has a bit of grain structure which i think is really interesting this was a piece of just air dried red particles the same stuff i sent to ben and it looks absolutely stunning while other pieces are just a totally flat red color but if we want to see nice big grain structure we're going to need to use a different method of stacking the particles to do that i let one sample sit and settle out over several weeks in a vibration free spot this sample used red particles but you can see that bright green and blue streaks as the main color you can see this looks much more like real opal with big distinct areas of color and bright play of color as i move around both commercially and in the literature the way this version is done is normally in large tall settling tanks where a very dilute solution of particles is used this way the particles take a long time to settle out and give the best grain size that looks the most like real opal most literature says about 7 months is the ideal settling time but i didn't actually understand that time frame until i tried this turns out that 7 month time frame has very little to do with the formation of the opal pattern itself as i found out in my experiments it forms the opal pattern in no more than a couple of weeks instead that long settling time is because if you try and dry out the opal after only a few weeks it's far too delicate just the action of the solvent evaporating moves the particles around and ruins the pattern so you just get left with a useless solid white chunk that in my case flashes red but if you leave it longer the sediment slowly firms up as it compresses down over time while maintaining that large grain structure so it's actually possible to dry it without ruining the pattern i've saved several samples from all these different runs that i'm allowing to settle out over several months so i can try drying them again but for now that means i'm stuck using the centrifuge method one quick note is how you make simulated black opal with this process and the secret isn't really that surprising before either spinning the particles down or letting them settle you just mix in a small amount of carbon nanoparticles not so much that you mess with the settling process just enough to add some contrast and those particles are really just made by holding something over a flame and collecting the soot and then filtering the soot to get the size particles you want you can also add dyes to the mix to make the opal have other color backgrounds now drying is actually in my opinion the trickiest part of this process that i honestly never got right in my case i just let my centrifuge samples air dry overnight by removing the lid from the tube but the pellet does shrink a bit and has a tendency to crack and i lost a ton of samples to this problem so industrially this would obviously be unacceptable especially with large samples this cracking can ruin months of waiting for the opal to be ready to get around this commercially the final opal is dried supercritically nile red recently did a video about supercritical drying but in his case he used compressed co2 as his solvent to dry out some aerogel but opal is too delicate to use co2 as the flowing liquids would disturb the particles so instead once the final opal is ready they load the entire settling tank into a special drying chamber and put it under 10 000 psi at 300 degrees to turn all of that ethanol into a supercritical fluid which they can just directly drain away if you want to learn about how supercritical drying works i'd recommend checking out niall's video but the key difference is that 10 000 psi is crazy high pressure much higher than what he used that's closer to the forces on the barrel of a gun when it fires but maintained and kept hot making the drying chamber very very expensive as it has to basically be a big hunk of steel so it doesn't explode now i'm a bit of a nut case so i'm actually looking into making such a drying chamber because at those pressures you're well into the regime that other crystals like emerald or amethyst can be grown at so if i do end up building it i'll be able to dry the opal samples i've got settling once the pellet is dry it's decision time if you want to make something which is identical to real opal you're going to need to center the particles basically this means heating them up to about 800 degrees which is just enough to slightly melt them so they fuse together but not so much that they actually melt and ruin the structure this makes the opal much stronger then you need to fill in the gaps between the particles with more silica though it's unclear from the literature how that's actually done opal made this way is called gilson opal after the guy who invented the process and we'll talk about him in a second but doing so requires equipment i just don't have right now the alternative to that is to take a page from peter brown's book and fill the opal with resin but this is a treacherous task what you ideally need is a very thin resin but all i had on hand was uv resin and art resin both of which are still fairly thick art resin is nice and easy to work with but doesn't actually seep into the opal structure at all so when i went to sand away the excess the second i hit the opal layer a large amount of opal crumbled away uv resin is better as it actually seeps into the opal a fair bit but had a tendency to make the opal crack even more which is very frustrating and i lost a really nice sample to this in the end i haven't found an ideal solution to this problem so if you have suggestions leave them below but for the sake of it i'll talk about what i did with the art resin and uv resin i also tried sodium silicate but there must have been some ammonia or something left in the opal because it hardened on contact and didn't penetrate in leaving a crunchy useless shell and ruining the opal pattern before that though i will say figuring all of this out was a massive pain in the ass when pierre gilson made the first synthetic opal back in the early 70s he did what any good capitalist would do and kept the secret to himself which if you've watched this channel for any length of time you know is not something i'm going to let stand the technology was eventually sold to the kyocera company who kept tight-lipped about the process since then people figured out various parts of the process but it still mostly kept his trade secret there is only a very small handful of papers and patents about making opal many of which were written by a group of very clever russian researchers though this does mean that very few of them are in english or easy to search for it took ages to find enough resources to actually stumble my way through this and i'd link to the best of them below the rest i had to figure out by doing the actual experiment and messing with it and it took a few attempts to get it right as you can imagine this quickly burned through my tos supply so luckily nile red is a saint and let me use some of his in settled opal you'll notice that the grains form this tall column structure this is actually really common in synthetic opal and so most are cut to be viewed from above to hide this pattern that long tiger stripe pattern is one of the things that gives away a synthetic but apparently there's some magical way to make that not happen but of course it's trade secret and will take a lot more effort to figure out even though it was stinky and quite frustrating at times i did very much enjoy making this video because i finally hope that this can serve as a good resource that people can reference when attempting to do this now it should be much easier for people to build on this and do things like figure out how that non-tiger stripe opal is made or find good solutions to the resin problem currently there's only a few companies that make opal and getting info out of them can feel like bleeding a stone at times now back to the casting process for the art resin i mixed up about 20 milliliters of resin and degassed it thoroughly in my vacuum chamber before pouring it over a sample of opal which i'd put in a little silicon mold this was then again vacuumed to try and force the resin into the opal but evidently that doesn't actually work very well after that i sanded it with regular sandpaper and then polished it with micro mesh polishing pads i actually learned about these pads from peter brown and love them for getting perfectly shiny surfaces on plastic and metals i have a second opal that i just kind of left in the raw resin because i didn't want to risk ruining it before i could show it off i'll get around to grinding off the excess later but it's just so pretty i didn't want to risk wrecking it before i could film the video for the uv samples i also use the vacuum chamber to force the resin in and this time it's clear that it actually penetrates into the opal structure before curing i fish the pieces out so there isn't a ton of excess resin to remove which made this way easier then they were just cured under a bright uv light for 20 minutes to make sure that they were well cured after that it was back to sanding and polishing just like before before i wrap this up and show you the final opals i do need to take a second to thank the sponsor of today's video which is nordvpn we talked a lot about faking something valuable today and never is that more of a concern than on the internet for those that don't know nordvpn is a virtual private network service that is an important way to protect yourself while you're online normally when you're browsing you connect directly to a website but when you do that your isp and whoever's wi-fi you're using can see what sites you're browsing they may not be able to see what you're doing on those sites but just knowing what sites you visit can tell you a lot about someone let's be honest we all look up weird stuff when we're in college or i suppose these days when we're bored and stuck at home nord acts like a middleman so instead of directly connecting to the next site on your internet rabbit hole you first connect to nord's super fast servers and that's all your isp or other people watching can see from there your traffic is forwarded to your site of choice and you have much more privacy the other great part of this is that it can unblock sites which may not be available to you here in canada i often get this annoying message that says certain videos or sites aren't available in my country using nord's more than 5 500 servers in 60 countries you can 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revisit this someday and end up making that crazy drying chamber if i do there'll be a few more gemstones to add to the list so to make sure you don't miss those the sapphires diamonds and litany of other projects i've got coming up then be sure to subscribe and of course i've put links to everything below if you want to learn more before i go i need to thank the amazing supporters of this channel that make these videos possible my patrons channel members and supporters on kofi are the main things that help me do amazing projects like this and i am so grateful for their support they also get access to the supporter discord so if that's something you're interested in or just want to help keep the flow of science videos coming there's some links below if this is the first time you heard about these projects it means you're probably not following me on my other social media platforms and you should probably do that that way you can see these projects and more long before they make it into videos that's all for now and i'll see you next time

Channel: The Thought Emporium

Views: 946,955

Rating: 4.9439511 out of 5

Keywords: opal, synthetic, nanoparticle, synthesis, resin, chemistry, art, craft, tutorial, stober process, science, photonic, nanostructure, structural color, bragg diffraction, diffraction, nilered, smartereveryday, applied science, vpn, nordvpn, colorful, color, rainbow, gem, gemstone, gem stones, chemical, TEOS, silica, silicate

Id: d7MvGFX_VKo

Length: 26min 16sec (1576 seconds)

Published: Fri Dec 04 2020

Reddit Comments

[u/Round-Ad3278]

nice