Blacken-It residue?

It sounds like you have to stop the chemical process. Washing it in water will help but is it an acid? If acid then an alkaline will work like plain soap. If it's an alkaline then an acid will help like lemon juice or vinegar.

I think that stuff might be an alkaline so the baking soda will work and/or some plain detergent/soap and water to soak it in. As long as the chemical process is stopped. Anyway I would use a lot of water to wash anything/everything off before I put anything else on or a sealer.

Then I would seal it all with dullcoat.

I read someone used that stuff and the tracks disintegrated, was it you?

I've had to soak them in soda water to stop the blackening process, then clean them by putting them al in a baggie and gently shaking together. Once this is done dullcote works to keep the coloring correct, or I use pastels and washes to do the same thing.