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Post by walterwhite on Aug 5, 2018 15:49:24 GMT -6
The first round of glaze tests went well. This time not so much. All of the glazes on the bottom of the kiln were duds, however one of the same glazes that failed on a tile worked out on the inside of a bowl. The only difference was kiln location, the glazes that worked were sparcely packed in the top half of the kiln. Could the densly packed lower half of the kiln gotten to hot/held too much heat? Was my application shotty? Glaze is Fa’s cone 6 Zinc-25 Dolo-5 3110-51 Frit-19 Lith-3 Firing schedule in Fahrenheit 350/h to 700 with 0:00 hold 9999/h to 2000 with 0:00 hold 150/h to 2210 with 0:10 hold 9999/h to 2000 with 1:00 hold 9999/h to 1900 with 1:00 hold 9999/h to 1990 with 1:00 hold 9999/h to 1900 with 1:00 hold Any hints would be awesome Here are some pics. photos.app.goo.gl/XTEUiqFuSN12ts6Q7 |
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gczop
Full Member
Posts: 202
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Post by gczop on Aug 6, 2018 11:22:56 GMT -6
Hi Walter,
Suggest you carefully read Arnie's comments.
Most folks start with a generic base mix and tweak it to suit their particular process variables.
I'd start by dropping the dolomite, MgO may or may not act as a flux at your temperatures.
Simplify.
Gordon
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Post by walterwhite on Aug 6, 2018 11:59:18 GMT -6
Hey gordon, thank you for your response! I had luck with that recipe but with a different ramp. Ill get back to the drawing board.
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Post by tileman2 on Aug 6, 2018 18:31:31 GMT -6
Walter:
There is a standard rule in crystalline glaze: change only one thing at a time. Change your firing schedule, but not the recipe. Or change just the zinc, just the frit, just the lithium. If you change multiple parameters at one time, you will not know which caused the result. That said, most crystalline recipes I have seen have a maximum of 2% dolomite. Secondly, cobalt tends to act like the rabbits down in the meadow: they like to multiply. I tend to cut back on zinc (24.5) when I fire mainly cobalt. Yes, packing density can play a role in over population.
The one thing you need to do is calibrate your kiln: if you have not already. Which means multiple cones on every shelf from top to bottom. This will tell you the hot and cold spots in the chamber. You may very well need to do a TC (thermocouple offset) to adjust your temp read out in line with cone results. My larger kilns have nearly a 40F degree offset, the smaller ones 15-20F. It's a learning curve that never ends.
T
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Post by walterwhite on Aug 6, 2018 23:27:12 GMT -6
The only thing different i tested in this one was the firing schedule and different colorant combos. I made some more tiles to see if that was the case.
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