can't figure out what I. did different

[Michael Stevens]

I added mica powder and it created beautiful blue bubble, but now I'm getting dark black lines and some spots of gold in. the center. I'm. not sure if I changed heating schedule, mixed different portion of powder and glycol, I'm. trying to duplicate result but can't understand why things are different

[Brad Walker]

You sure it's mica powder you added? Looks like copper or a copper oxide.

[Michael Stevens]

maybe it has additives but it's gold mica powder. did I not fire hot or long enough, is that why center stayed gold color? or the black lines is that from contamination with other powders?

[Brad Walker]

Generally, blue bubbles come from a copper compound. They'll give you the beautiful bright blue bubbles in your piece. If you put too much copper (usually copper oxide) it will have black ugly areas like your other piece. Firing too high can also cause this problem.

My guess is that the mica you're using has come copper oxide in it. Try using less of the mica and see if you get a better result.