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Electroforming gold jewelry on copper, and can't remove last traces of copper

Hi I am goldsmith I work in gold tube bracelets and necklaces,we start the work by coating a copper rod of one c.m. diameter ,with a plate of gold of 0.05 mm. thick,then we continue the process by lowering the diameter of the copper rod which is plated with gold to nearly 0.15-0.2,then we make the bracelet, and after finishing completely we put the bracelet in nitric acid in order to get rid of the copper inside the bracelet,the question is, a thin layer of copper is still sticking to the gold from inside the tube,which is causing to lower the degree of gold,the nitric acid is not cleaning completely, so may someone can show me a way to get rid of that thin layer of copper, will be very grateful

Gar SHAH
PRODUCT DESIGNER - BEIRUT, LEBANON
April 26, 2010

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April 27, 2010

Hi, Gar. There may be a good reason why you do what you do (my knowledge of jewelry making is limited), but why are you electroforming on copper instead of easier to dissolve materials like wax or aluminum?

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

u boil the jewellery in nitric acid.use 71% pure nitric acid.

Bhupesh Mulik
jewellery - Mumbai, India
May 5, 2010

H2SO4 3 parts and nitric acid 1 part

Majed Janineh
- Beith Lehem Palistain
September 27, 2011