Hi. I operate as a finisher and patinater at a four person foundry in London, UK. I depletion gilded a silver cast Mastadon tooth for a client (first time doing this) and it worked well after 14 pickles. However, after a brief soak in bicarb solution, I am getting green liquid leaching out porosity and the small hole drilled before pickling. I have warmed the piece gently on a radiator. Is this really down to not soaking in bicarb long enough or should I be doing something else?
Many thanks, Matt Borthwick
Matt - when you complete the pickling process, I recommend boiling the piece in baking soda and water for at least an hour. then let it cool in the liquid. Rinse well with plain water. If you can see the void from which the green liquid is leaking, use a fine hypodermic needle with baking soda solution and squirt it into the hole repeatedly. Rinse with plain water several times using a hypodermic needle to flood the void. Dry the piece with compressed air. That is the technique that is used with hollow formed pieces.
Like Judy says, that’s residual acid causing the greenish gunk to leak out, and her method of injecting baking soda solution sounds like a good cure. And that’s a Megalodon (shark) tooth, not a Mastodon (elephant).
Thanks very much everyone! Will get on it tomorrow.