I decided to go ahead with the treatment. I had
two coins with a thin layers of horn silver covering large areas and one coin with two patches that I thought might be horn silver. Unfortunately I did not take any pictures.
I prepared a bath of 10% sodium thiosulfate and 90% distilled water, and another bath of 100% distilled water. Sodium thiosulfate dissolved very easily even without heating up the water. I started with one coin but eventually had
all three in the bath at the same time. I did not let the coins touch each other.
The effect of the bath was almost instant. You could see areas turning dark when the horn silver reacted with sodium thiosulfate. The speed of the reaction surprised me and I took the first coin out after just 30 seconds for the first distilled bath and brushing. Brushing removed the dark crust that had
formed as a result of the reaction. Most of the horn silver didn't turn dark, only somewhat dimmer.
read that extended periods of time in a sodium thiosulfate bath could cause toning
so I soaked the coins in 100% distilled water whenever I brushed them. I used a soft toothbrush with trimmed bristles. This worked perfectly and left no marks on the coins. I kept cycling between bathing and brushing with few minutes in the bath at a time and eventually a final 10 minute bath followed by the final brushing. Overall the coins spent probably around 25 minutes in the solution though I think in this case only Coin 2 showed signs of improvement after the 5 minute mark. Most of the horn silver was removed during the first 2-3 soakings.
I do not have pictures so a verbal description based on my initial impressions will have to suffice. This is not ideal and I apologize for that:
before: Half covered by a thin layer of horn silver, other half bright with no encrustations. Sharp
before: Bright with no encrustations. Sharp
after: No visual changes to the areas without horn silver, areas with horn silver brightened and cleared up. There is slight roughness in the areas that had
horn silver and the surface is still
dimmer compared to the unaffected areas with one 1x2 mm darker spot. Even sharper details were revealed from underneath the horn silver.Reverse
after: No visual changes
before: Most covered by a very thin layer of horn silver with some thicker areas on one side
. Details pretty sharp
before: Two patches of horn silver, covering about 1/4 of the coin. Details sharp
but also hazy in the areas with horn silverObverse
after: Slight roughness especially in the areas that had
thicker layers of horn silver. The surface is overall brighter and clearer than before, though still
dim. The surfaces seemed to improve further once the coin had
a chance to dry. Much of the haziness in the details is gone. Reverse
after: Brighter and clearer but the rough surface revealed underneath doesn't reflect the light as well as the horn silver did so the patches are more visible. One small darker spot also about 1x2 mm revealed underneath. The details sharpened up noticeably. No visual changes to the areas without horn silver.
before: Dark toning
with no encrustations. Sharp
before: Dark toning
details. Two patches of 3x5 mm and 2x3 mm that are either encrustations, horn silver, or some combination of these with maybe some corrosion thrown in. Obverse
after: No visual changesReverse
after: Very slightly sharper details revealed from underneath one of the patches. The surface is now clearer but rough similarly to what was revealed with the other two coins, suggesting that the patch was horn silver. Toning
in the area
lightened up just a bit
. No radical changes to the other patch, possibly a very slight improvement in the sharpness of the details. No visual changes elsewhere.
Overall the treatment was a success
. I anticipated much worse, though admittedly the horn silver layers were fairly thin.