Too tired to tell the full tale just now. Maybe later. [Updated below]. In the meantime, behold the before-and-after pics, and weep with/for me. This was my childhood treasure- I got it for my 11th birthday. 3 years between pics. Before: Today:
As you probably know Rob, like many of us with ancient bronzes, a bath in distilled water and gently remove the powdery stuff then a long, long soak (can be weeks or months) in clean, regularly changed, distilled water can halt the oxydisation process at least. After thoroughly drying inspect it on a regular basis. Store it in such a way as to have no, or as little as possible, contact with moisture. Repeat if required. Regrettably, I think there will be little corrosion dots in the metal under there. Shame, but the coin and its memories are still there, picture it in your mind as it was, not as it now appears, as difficult as that might be.
Oh my. So sorry. You know even in a safe, moisture can get there. In Louisiana anyway. Put this where some coins are. You will find out exactly how much moisture is there in a matter of days.
Lord, I've never seen anything like that on a coin...looks like penicillin culture! Does anyone know exactly what caused this? J.T.
I suspect a very moist southern environment.... Not that our Lord intentionally left the piece in a damp place.... But come July and August down this way you have to swim from the front door to your car the air is so thick with humidity.
Hi Randy, I live in Houston, not known for it's dry heat, and none of my 3 yr. old silver U.S. coinage looks like it caught an unheard of yet Covid strain. J.T.
I think he had this one in a storage house with some childhood memory type stuff. I don't think he had the piece in a temperature controlled environment.
I agree with @expat, see if you can loosen that before it really gets hold. Then Verdicare it, maybe. That’s like an outbreak of measles. What a shocker!
Oh no. It seems this coin has sentimental value to you. If it were mine, I think I'd spend the money to have it conserved and slabbed, hoping to keep it in as pristine condition as possible.