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  1. The story thus far... Is kind of long. I understand some glaze chem at cone ten. This cone 6 business is a different animal. I need a cone 6 clear glaze that is rock hard, food safe (no crazing after a freeze test), compatible with underglazes and Mason stain washes, and is crystal clear over red clay. After begging a few recipes from friends and off the internet and doing some initial tests, I've found that the main barriers to hitting all of these points are microbubbles that seem to be present mostly over the red clay indicating the glazes are melting before all the carbon has burned off, boron clouding, and some crawling off of the stain-washed areas. I am cutting my mason stains 50% with gerstley borate, as this has been giving me better brushability than straight frit. I am willing to alter the stain vehicle as needed. I'm not having too much trouble with glaze fit (yay!). My clay body is Plainsman m390, with some use of m370 as a white slip for contrast/texture/better canvas for colours. So far, the recipe that seems to have the fewest problems is from digitalfire, the Ravenscrag clear mix of 80% Ravenscrag slip, and 20% Ferro frit 3134. This iteration had some microbubbles over the red clay areas (not the white) and it was suggested to me to flux the glaze out a bit more, after an initial test showed firing with a soak that brought the kiln to cone 7 did clear some of them. Higher percentages of the frit did get rid of the microbubbles, but brought in boron clouding instead. At this point, I'm heading to Insight, because enough with the testing of random recipes. I need to narrow the field before I put brush to test sieve again. The only information I could dig up on eliminating boron clouding was from various points all over digitalfire, and pertained to low-fire temperatures. I can only assume that the soloution offered of raising the alumina will apply just as well at cone 6. (unless someone knows of a reason otherwise?) So boron + not enough alumina= boron clouding. If I'm sourcing flux from frit 3134 (high boron, no alumina), and the only other material in the glaze is Ravenscrag (a complete glaze at cone ten that needs flux to melt it at cone 6), how to get more alumina? I already have frit 3110 (high boron, some alumina), but just swapping that out straight across the board actually takes the silica:alumina ratio lower (the boron/silica:alumina ratio stays the same). So that doesn't fix the problem. So how about adding lithium to replace some of the boron? I have in my posession petalite and spodumene, sources of both Lithium and Alumina. Here's where my understanding breaks down. Just as a starting point, if I change the 20% frit from the original recipe from 3134 to 10% 3110 and 10% Spodumene (see screen shot), things look pretty good on paper. The Alumina:Silica ratio is way better, there's almost no boron to cause clouding, the expansion rate seems pretty good, and both frit 3110 and Spodumene begin to fuse at a higher temperature relative to frit 3134, giving the clay body time to off-gas and fix any potential bubble issue. But have I taken my fluxes too low? How badly is the lithium going to mess with colour response? I don't totally know how to interpret these in relation to the limit formula (pink column on the right). Is anything else seriously out of whack that I'm not looking at? Help!
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