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Want consistent 2-tone plating on acid tin

hi sir,
I am khande.rakesh from jaipur, we manufacture brass jewellery. We prefer 2-tone plating. We recently tried acid tin(stannous sulfate),after plating we dip the piece into anti-tarnish tin solution(passival-80) and took it under steam machine after the piece is dried we applied masking where it is required after the masking is dried we took it for yellow bronze and then for gold potassium cyanide.but after 2 days when I saw the piece the golden portion was no more it had a pale yellow colours on few places please suggest me and get me out of this problem.

thank u.,

Khande Rakesh
jewellery manufacturer - Jaipur, Rajasthan, India
November 10, 2008

If I understand your question, the problem is that the gold is not a rich gold color, but a pale yellow in spots. Yellow bronze is not a very good barrier plate between the tin and gold. White bronze or nickel would be a much better choice. The gold plated layer is most likely so thin that the yellow bronze is migrating through the gold layer, giving it the pale yellow color you are seeing. Try a different diffusion barrier plate, you will have better results.

Mark Baker
Process Engineer - Syracuse, New York
December 3, 2008