Yep another pot had some cobalt on it, a stain probably of pure cobalt powder mixed with some water, on greenware. Yuk, it leaves that trace almost invisible until it's suddenly found on all kinds of my bisqued pottery when it comes out of the kiln.
I've stopped using cobalt stain, because of just this. A few years ago I put a dress on a woman in cobalt, only to find her skin had also become blue.
These were sanded down and a glaze with various colors was used on them, hoping that the cobalt prints won't show as much and they might be salable.
I'll let ya know!
