Restore Antique Gold Coin's Patina: A Guide to Darkening Gold

Question
Hi,
I have a coin of mid 1500s which is gold, the previous owner had a slight repair to it and after which it was polished, The polishing of the coin makes it look unatural and i would like to get it back to a dull looking coin (without the shine) is there something i can do or put on it to make the shine disapear. If there is something that works quickly rather than having to wait a long time i would be grateful for all options.
Kind regards,
Mark

Answer
Mark,

It sounds like the coin may be less than pure gold.  Only base metals oxidize and go darker.
If the coin has copper, silver, zinc, nickel etc. as alloys these can cause the metal to darken due to oxidation.

One idea may be to heat the coin up to 1600 F and let it cool in the open air.  The heat can cause oxidation of the base metals in the alloy.  This process could repeated to age the coin if you will.

Hope this gives you some direction.

Regards,

Steven D.Covey