Crazing?

I'll have a stab at it...

I would say your silica IS quite low. for my 3110 frit glazes my silica is anywhere between 17% to 26% and the ones below ~21% do craze some whereas my silica amounts higher than that being minimal to none in crazing.

Not saying that is the solution though.

Perhaps a switch in clays will help.

For us our glazes that do not craze on Coleman porcelain, glacia or b-mix, will do so on others like miller, helios, suziki and pier porcelain, in different amounts of course. (miller being the worst by far.)

But we have also noticed that simply getting the glaze to stay on the pot a little thinner helps prevent crazing too. Whether it be a thinner application, or firing a little hotter or fluxing the glaze some. Firing hotter and fluxing usually require other changes to the glaze later though as they may alter the outcome of the crystals.


just some thoughts.

G

If you use casting slip  use more Quartz in the slip recipe and more Quartz in the glaze recipe too.
I allways wonder the glaze recipes use these like numbers you wrote.
Why do not write :
Fritt 48 %
Flint 18
TiO2 8    .....



You measure out exactly 
the following amounts ?
Frit 3110 ––––––––––––––––––– 48.4%

Calcined Zinc Oxide ––––––––––– 24.35

Calcined Kaolin –––––––––––––– 1.52

Flint –––––––––––––––––––––––– 17.95

Titanium Dioxide ––––––––––––– 7.78 

It may seem off reading the percentage but the actual weighted number is usually whole. In large batches, those small percentage differences add up and cause unwanted ratios.

Thanks Ferenc and John. The recipe, with all its exactitude, is directly from David Snair, and I rather like the two decimal places of accuracy. I apply some laboratory science to what I do (primarily out of obsessive/compulsive habit from directing medical research labs). Not having great quantities of expensive metal oxides and carbonates on hand, I use those exact measurements when mixing micro-batches of glaze. I weigh the ingredients sometimes to +/- 5mg, so employing that precision I can make just enough for a single test tile (not for crystalline, however. That's an entirely different animal I've just gotten into the cage with).

John, is that some form of spread sheet you've posted a screen shot of? If so, it looks like something I could use for percent calculations rather than the hand written formulas I now use.

I supose i'm a creatan but i mix my glazes in 25 lb batches and frequently make adjustments  by throwing in a handful of something mid batch, one of my favorite glazes is my scrap batch which includes all the residue on my glazing wheel ,overspray and the scraping off the floor Which includes the liner glazes and everything else

this has my scrap glaze under a silver bearing glaze

That's both amazing and tragic. Amazing because . . . well, that's self evident in its beauty. Tragic because you don't have the recipe.