Warning: Sodium hydroxide is corrosive. Wear gloves when handling it. In addition, the chemicals wastes may generate hydrogen sulfide if acidified. Destruction with bleach is recommended. Greetings fellow nerds. In a previous video i was restoring tarnished silver with electrochemistry. I was doing it repeatedly and it seemed like i had dozens of tarnished silver coins off camera. Actually it was the same coin and i was re-tarnishing it over and over again. In this video we’re going to see how i did that. First i need to issue a warning to any silver collectors, coin collectors or antiques dealers. Artificial chemical alteration of silver is very poorly received by the collector community in general. Do not perform this on any pieces of metal that have any historical, numismatic or other value beyond the spot price of the silver metal itself. Our objective in this video is to explore the science. Now i actually showed this years before as part of my silver anodizing videos. The process isn’t much different except now i’m doing it in higher resolution. If you’re already satisfied with that video then you can skip this one. So let’s get started. First we need to make our anodizing solution. Start with 200mL of water and stir in 10g of powdered sulfur. Then add in 20g of sodium hydroxide. You may have to increase stirring to get the sulfur to mix. What we’re doing is making a mixture of sodium polysulfides. Keep stirring for about half an hour or so. Afterward filter the mixture to remove any excess sulfur. Here i’ve poured out the anodizing solution into a shallow petri dish. Now we’re going to need a battery for this to force the oxidation of the silver. I’m using just a single 1.5 volt battery since it works slower and let’s us better control what we’re doing. And here is our silver coin. Technically this is a silver round but the chemistry is the same. To do the anodizing or toning as it’s sometimes called, we connect the coin to the positive end of the battery and make it an anode. Now we just touch the negative end or cathode to solution. And there we go, years of tarnish made in just a few seconds. What’s happening is at cathode we’re just generating hydrogen gas. But at the anode we’re oxidizing the silver and combining it with sulfide ions to make silver sulfide which is the tarnish you see on silver. Now let me try again but this time for longer. The final color is dependent the thickness of silver sulfide layer. If you run longer, you get a thicker silver sulfide layer and different colors as well. This is because the light undergoes interference with itself as it partially passes through the layer. Depending on the thickness, certain wavelengths of light are destructively removed and others are not. And there we go. Beautifully toned silver. Let me wash it. Now the color changes slightly as it’s exposed to air since the reactions keep going. It takes a few hours for it to settle on the final color but you get the idea. And there it is a beautiful blue toning. You can even see purples, a bit of green, and some reds in there as well. A naturally toned coin is considered very valuable by collectors. But artificially toned coins like this one are considered cheating and only worth a little more than spot price. Now a special note about this particular coin. You’re probably wondering what’s with this splotch right here that never seems to change. Well this particular coin was the same coin i used for silver testing with that acid dichromate solution i made in a previous video. The test etched the coin so badly that it’s been deeply damaged. That splotch is a sandpaper like surface and while it is being tarnished as usual, it’s so rough that we can’t see any difference. This is why you don’t run silver testing on visible or important parts of a silver item. The damage is extremely unsightly. Anyway let’s get back to our current experiment. Let’s try a different procedure now and use six volts of current. This will give us a faster conversion rate but also create a much high current density and polarization on the coin. This will allow us to create different patterns based on that. I’m going to hold the electrode well off to the side of the coin rather than just above it to make the current density as uneven as possible. And there we go. We now have a rainbow coin. The areas closest to the cathode tarnished and changed colors faster than the ones further away. This creates this rainbow gradient pattern. Let me try that again. But rather than distance, i’m going to simply hold my thumb against the coin and directly block the current that way. As a side note, when you’re using a positive current to thicken a layer of oxides, or in this case sulfides, on the surface of a metal, the process is called anodization. Anyway there we go. And you can see where my thumb blocked the current. You can get all kinds of interesting artistic patterns this way. Now you might be wondering what happens if you go too far and run the current for too long. What you create is black silver sulfide. The silver sulfide is loosely adherent and comes off. But it contains silver so we’ve lost it and in doing so this damages the fine details of the coin. Kind of like sandblasting except we’re using ions. Additionally, electrochemical restoration doesn’t work very well with this extreme level of damage. You end up having to grind off the silver sulfide causing even more surface damage to your coin. So if you’re doing this for artistic purposes then be sure to practice a lot with silver you don’t mind damaging. Then move on to doing it your target piece. Anyway a special note on waste disposal. This solution of sodium polysulfides will release hydrogen sulfide if mixed with acids. To render it safe i recommend adding in half a liter of bleach to oxidize the sulfides into sulfur and sulfates. If you want to avoid sulfur you can actually try the same experiment with just sodium hydroxide. Now this produces silver oxide rather than silver sulfide. But the experiment works very well and you still get great color. It’s not quite as well defined as using sulfides, but i’ll leave the choice up to you. Anyway, that was artificial silver toning or tarnishing based on anodization. Thanks for watching. Special thank you to all of my supporters on patreon for making these science videos possible with their donations and their direction. If you are not currently a patron, but like to support the continued production of science videos like this one, then check out my patreon page here or in the video description. I really appreciate any and all support.