Create Ancient Coin Patinas With Sesquicarbonate

To add a patina to your coins I suggest a method that conservators use.
A 4% Sodium Sesquicarbonate bath (20 grams of Sodium
Carbonate plus 20 grams of Sodium Bicarbonate in 960ml of distilled water) soak the coin in this solution 2-3 weeks until coin is darkened.
Heat may also be applied to the solution to accelerate the process.
After this phase handle the coin with rubber gloves
to not contaminate the coin with salts from your skin then place in a bath of fresh distilled water for a day to remove the Sodium Sesquicarbonate.
Next dehydrate the coin in three baths of alcohol.
Let it soak in each container at least one hour. The first two
containers of alcohol may be reused for other coins but the last
container must always be fresh for each coin.
The final phase is sealing the coin with renwax and
placing in a non-pvc coin flip.
Method Source:
The Archaeologist's Manual for Conservation A Guide to Non-Toxic,
Minimal Intervention Artifact Stabilization
Rodgers, Bradley A.
2004, 220 p., Softcover
ISBN: 0-306-48467-6
-Shawn (aka The Lone Knight)