How do you treat coins that has white rust (I'm not sure this is how it's beeing called)? I have these two coins, one is a Ptolemy, the other is a Prutah, both have some white powder/rust on it. I cleaned it with some toothbrush but after a few months it's back again
Soak in distilled water after removing corrosion for a few days. Change water and try again. Not regular water.... but distilled water. Then try this as a final treatment... Verdicare. I like Verdicare so much that I even treat every single coin I receive with it before storing them away, even though they don't have any BD. I do it as a preventative measure. I've yet to have a single coin that I treated with Verdicare develop any bronze disease, and I live in humid Florida.
That is where I would start too, but order some Verdicare for the second portion of your treatment. And in the future when you get a healthy coin, a quick preventative treatment with Verdicare should also be part of your routine...at least for bronze coins.
I always connect "white rust" with zinc coins. Look at WWII low face value coins. I also connect it with aluminum coins. Zinc and aluminum are highly sensitive to oxygen, particularly in moist conditions. For zinc coins "white rust" is a continuing process. For aluminum coins "white rust" actually stops after the coin is completely covered. The coating actually seals the coin from further oxidation. But that doesn't make the coin look any better. My guess is that 2x2's and Air-tites and Cointains would offer the best protection. Flips are still open to the air.
With proper removal of BD, followed by a soak or two in distilled water, and Verdicare treatment, the coins should never show signs of BD again. If they do, then you weren't thorough enough and should repeat the process one more time. You are dealing with ancient coins here. They don't need airtights. And the oxidation process he described are for modern coin metals, not ancient coins. What you need to do is remove the corrosion and neutralize the salts that are interacting with the oxygen to cause BD. Once you do that, the coin should remain stable indefinitely. You know how to cure the coins now....so go get the tools and have fun at it. Note: Make sure coin is completely dry after distilled water treatment before Verdicare. Let the coin dry out for a day or two. Also, Verdicare treated coins should be dried up with a towel after no more than 24 hours. I've accidentally let a coin soak in Verdicare for 3 days by accident with no ill effects, but instructions say no more than 24 hours.
Question. I would think the first step would be an acetone bath. That would get rid of oils, dirt, etc. That would leave the coin in the best shape for your suggested further treatment. Last thing you want is some glop of something blocking further treatment.
No! No acetone on copper, bronze, or billon coins. Keep acetone away from any coin that's not at least 50% silver, otherwise you will be very disappointed with the end result. Distilled water is best for those coins. Last time I dropped a bronze ancient in acetone (by accident as I was working on some silver coins at the same time I was handling that bronze coin) the patina became dull as heck, and all character and color disappeared. It looked terrible. I was lucky that Verdicare made it look about 85% as good as it looked before the accidental dip in acetone. Otherwise I don't know what I would have done with that coin.
Only lead oxidizes (rusts) white - an example is civil war bullets & musket balls dug up while metal detecting:
The coins were left in DW for 48H and they do look better!! I just replaced the DW with fresh ones now and will give it some more time. Question: does the rule "longer is better" applies here? Should I leave it for longer period now?
You can leave it for longer. I know it sounds counterproductive because it's water, but distilled water undergoes a chemical reaction with the salts that are reacting with the metal to cause BD, and that reaction neutralizes the BD. I'm not a chemist so I'm sure someone else here can explain the chemical reaction process better for you than I ever could. As to how long is enough....not sure. I'd say a week might be enough, though am sure someone else here might have better experience with what time period is the best. I've only ever used the process on a few coins to remove dirt/grime, not treat actual BD, except for once. With BD, I only ever treated one coin, and I did a week of distilled waternafter manual removal of BD, followed by Verdicare. It was a very tiny spot of BD, and the coin has never suffered from it again. I do use Verdicare on all my coins since then, and have never had issues with BD.
