Warning: my attempt at a cobalt blue marble went totally purple

I was trying to make a classic cobalt blue marble for a paperweight at my studio in Tacoma, using a batch of glass from Northstar. After the second reheat, the whole thing came out this deep, weird purple instead of blue. I think my propane mix was off, maybe too much oxygen? Has anyone else had a color shift like that with cobalt, and how do you keep it true?

2 comments

2 Comments

troyjackson7d ago

Cobalt blue needs a reducing flame, not oxidizing.

the_henry7d ago

Yeah but that's only for the really deep blue.