18KY gold when filed becomes red

[purplepepper8]

Hi, This is made from 18KY gold, but when I used emery paper on it I saw that those sections are more red (sorry its a bit hard to capture in a photo). I think its because of something to do with the heating of the metal. Does anyone know the precise cause/ how i can prevent it? Thanks

 

[rweigel]

Most 18K yellow golds contain 10-15% copper. When you anneal those, copper oxide forms at the surface. Usually one pickles the annealed gold in an acid solution, which removes the copper oxide and leaves a copper depleted layer with a pale yellow or even greenish tint. Emery paper cuts throug this thin layer and reveals the original gold color. The contrast with the pale yellow layer makes it appear more reddish… The final color of your gold will only appear after sanding, wet brushing with a fine brass brush and polishing.

Possibility number 2: unhomogeneous alloy, that really has copper spots. Nothing could be done than galvanic Gilding of the finished piece or remelting and starting from scratch.

You could reduce the surface oxide formation by protecting the alloy‘s surface with boric acid or Pripp‘s flux. Also, do not anneal more often or longer than needed. Quench the piece in water, never in pickle, no matter how often you see this in workshops.

Cheers

Ralf

 

[purplepepper8]

Hi again Ralf, and thanks for your response. Yes once I proceeded to work the surface a bit more with sanding papers the redness reduced. I don't think the issue is unhomogeneous alloy.

I did add boric acid to the surface when heating but I think I just heated too much- the dome has a plate soldered to it and to get a perfect seal all around it was heated quite a few times so that couldve added to the issue. I’ll keep in mind to quench in water, thank you