Horn Silver Treatment on Eukratides Tetradrachm

[Cordoba]

I had bought a eukratides tetradrachm from roma a year ago, and it had a case of horn silver. It had progressively darkened, and got quite distracting, so I tried out sodium thiosulfate on it. It worked quite well, especially on the obverse. I have to thank Roerbakmix and his thread on cointalk detailing the process. The process was pretty simple, and I wasn't exactly scientific in measuring. I heated up distilled water, and made a solution of roughly 95% water to 5% sodium thiosulfate. The sodium thiosulfate would cause the horn silver to darken, and would come off afterwards in water. Below is the progression of the coin and then the after photos from cleaning.

Feel free to post any coins you've had luck cleaning, or bactrians 🙂

Several months after purchase

Right before cleaning

After cleaning

 

Edited November 17, 2023 by Cordoba

[Kaleun96]

Nice job! Interesting to see how much the horn silver darkened before you cleaned it. 

I see that after cleaning the coin has a yellow-ish dull tone to it. That often happens when cleaning with thiosulfates. In my experience it seems to prevent proper toning and can also give the coin an unnatural colour so I try to remove it. I haven't yet found a chemical method that removes it though. It can be removed by friction (e.g. using a small eraser), which won't polish the coin provided you don't do it a lot but it'd still be nice to find a better way of removing it than this. 

[NewStyleKing]

Would toothpaste be acceptable?  I found it works a treat!😀 Then I'm not very picky! Life is abrasive one way or another!

[DLTcoins]

9 hours ago, Kaleun96 said:

Interesting to see how much the horn silver darkened before you cleaned it. 

Horn silver (AgCl) darkens with exposure to light. This is the principle on which black and white photography is based.

[Kaleun96]

13 hours ago, DLTcoins said:

Horn silver (AgCl) darkens with exposure to light. This is the principle on which black and white photography is based.

And hence why you can often use photographic fixer as a source of sodium thiosulfate. What I'm surprised about is just the extent of it, not that it happens. I've just not seen one of my own coins with horn silver darken like that. Then again, on second look, I think the significant differences in the photography between the first and second photo may having the most effect on the apparent darkening.

[Roerbakmix]

Happy to have helped 🙂 turned out nice! 
the yellow colour can happen because the coin was immersed in the same solution. Sodium thiosulphates ultimately may cause sulphate deposits. 

Edited November 18, 2023 by Roerbakmix