White unsoluble foil pieces, what is it?

[Renaldas]

Several times I get this thin white foil pieces, they do not dissolve in AR, even in very hot. First time i face this question when I was refining 18K white gold necklace. Today it is 10K or 12K gold plated watches, white in colour. Tell me please, what is this foil and how can it get it dissolved?

http://www.youtube.com/watch?v=9_JpgXdOZGw

 

[Oz]

It is probably just some rhodium plating, be thankful. Rather than continue to try dissolving the foils set them aside and refine them separately when you have a fair quantity.