boardbutproductive
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Hi all! Question- About a year ago, I made a mug using velvet underglaze and zinc-free clear. In the past few weeks, I have noticed that the bottom interior of the mug has developed pinholes with little black dots, and the clear glaze has started to look a bit milky. (See attached pic)
The clay body is laguna cone-5 Bmix, fired to cone 5, so it should be vitrified. Any ideas what is going on here? Is it still food safe?
What are these little black dots?
in Studio Operations and Making Work
Posted
Thanks all-- I'm not sure if it's coffee or mold, but either way, I'm planning to refire it to see if that helps. I figure either it fixes it, or this mug goes in the bin like it would have anyway.
Amaco suggested decreasing the HF-9 glaze I used inside from 3 coats to 2, as they said it looks like the glaze pooled here, causing lots of little bubbles that eventually wore through. I plan to try that going forward, and also to run some tests with the orange underglaze. Everywhere I used that orange, it turned into a sort of orange-peel texture (no pun intended) after glaze firing.