This topic came up a few months ago and Paul Lewing seemed to have the best answer,
"Posted 25 March 2016 - 08:41 AM
The solutions to your problem that have been proposed have all been process or physical fixes, but the root of your problem is chemical. If you want glazes to bleed a long way into each other, they need to be very dissimilar. Conversely, glazes that are similar will bleed into each other less. And the key area of difference is Si:Al ratio. If the two have ratios have difference from each other that is greater than 6 they will definitely bleed a lot. For instance if one has a Si:/Al ratio of 5 and the other has a ratio of 12, expect a lot of bleeding. This of course makes sense. One is deficient in silica, the other is deficient in alumina, so the go looking for what they need in the other.
So... bottom line, if you want no bleeding at all, your best bet is color variations on the same glaze. Doesn't matter what glaze it is. The the only variable will be how much of a flux or refractory the colorant is in each different color variation."
An easy way to make your G1216M glaze more runny would be to just decrease the alumina, (epk in this recipe), test by running a line blend. It will increase the likelihood of crazing though.
- Saki likes this