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Clipboard a is a coin I have had for a while that I brought in Melbourne for about $90. As you can see the toning is uneven and detracts from the coin. Clipboard b is the same coin after sodium bicarbonate and Al foil treatment. The only treatment I know that does not damage the coin as it restores the silver oxides and sulfides back into silver metal. I know many collectors like an even tone to enhance the coin but in truth the toning on silver coins is corrosion that damages the surface of the coin. The colors in the toning are the result of optical interference between light reflected from the metal surface of the coin and that reflected from the oxide layer on the coin in a similar fashion to oil on a wet road. the silver oxide. I think a definite improvement.

1p