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I just opened my kiln and boy did I do something wrong!

I was doing an "enamel test" using 4" ceramic tiles (since I will be using the Ferro enamels on both ceramic blanks and glass) and it looks like I sprinkled salt on the tiles under the enamel.....lots of little bumps.

I thought I mixed the enamels very well and when they were airbrushed on the tiles it appeared to be a nice smooth even coat. When they were dry, I sprayed the flux on top.

I fired slow 300 degrees per hr to 1550 (which is approx. half way between the suggested firing range)...held for 5 minutes and then down(took about 6 hrs. to reach 1550). Since it wasn't glass I didn't worry about annealing etc. I have a new Skutt #GM1227 production kiln.

It looks as if either I didn't go high enough, or I should have held it longer at 1550....or both....or?

Help would be much appreciated as I planned on doing the glass test today!

Thanks,
Cathy

Cathy, I have to assume the tiles you used were glazed tiles instead of bisque tiles. In general the glazes on commercial tiles are fired considerably hotter than glass fusing temperatures. I would guess the maturity temperature of the glaze on your tile to be 2000 F or hotter. I am not sure how much the glaze on your tile is softening at 1500 F and how well the enamel you applied to it is fusing and adhering. Also, I do not understand why you applied enamel then flux over the enamel in a separate layer. In my experience flux is added to the colored enamel when it is mixed with medium to lower the melting point of the enamel. I am not familiar with applying frit over a layer of enamel. Do you have written instructions from Ferro telling you to apply flux over unfired enamels? The overglaze colors that I am used to working with on ceramics or porcelain are compounded to mature in a range of cone 018 to 014, 1350 to 1540 F.

Your texture like salt under the enamel sounds like you might have fired your enamel hotter than its maturity temperature and it bubbled. Adding flux to the enamel usually lowers the maturity temperature of the enamel. I would suggest that you should try another test on your tiles with just the enamels or with a small amount, 10%, of flux ground into the enamel when you mix it with your medium used to apply it through your airbrush. Do some additional tests and let us know how they come out. Also feel free to contact me by email if you think I can help you more.

Best wishes,
Tom in Texas

try doing the exact same thing on glass. then if it works (and it should) you will know the problems were with the tiles. when doing tests it is not a good idea to change more than one thing at a time. i spray hi temp flux over those enamels to even out the gloss. if you want to pre fire something at a low temp 1100f or so then mix the low temp flux with the enamels. rosanna

oh yea, spray the flux over 1/2 of the glass test and then you will know the difference. just arrange your colors so each gets some and none. rosanna

another oh yea, peek in at top temp if you can. the surface should look shiny and melted . rosanna

I can't thank you all enough. We have a big retail show coming up in three weeks and I really have to solve this problem. I will run more tests today and more tomorrow and will let you know what I find out.

Cathy