Hi guys. I've started my aquaitance with ceramics and glazes half a year ago. I still have a very basic understanding of chemistry and I have several problems I'd like to ask about.
First is clear transparent glaze. I made around 10 of them taking different recipes, but all of them contain bubbles. I've tried bisque firing in various temps, from 600 to 950C and second firing slow cooling, dropping and slow cooling, but bubbles are there and their quantity is similar in all conditions. I know commercial glazes don't have such problems. Please help me to figure out what is going on. My thought is that my raw materials are the problem. I have very few materials for glazes, those are: feldspar, whiting, borax, dolomite, talc, silica and kaolin. Substituting whiting with wollastonite didn't help. The runnier the glaze the less bubbles it has, but running is provided with whiting and borax and I have white clouds coming along with bubbles. Less flux - no clouds, but still bubbles.
I imagine it is kaolin that gives a lot of small bubbles. Any chances to fix that?
I have stains and wish to use them in underglaze painting, so I need to make a decent covering glaze.
For underglazes I bought a few frits, I don't know their formula, seller keeps it in secret, only mentioning temp range. I have 1 lead flux frit melting on 710C and other leadless on 1100C. I need to fire on 1220C, so I guess some kaolin may help to lift temp of frits melting so the stains won't burn out, but more bubbles again?
If you have info how to win the fight with bubbles please share.
Sorry if made any mistakes.