From Scribbles to Success: Fixing This Glaze Recipe

Monday 20th August 2018

If you do DIY pottery glazing you may have recipes scribbled onto cards like this. But the card is not the big issue here; it is that recipe! It really needs some work. Here is what could be done.
-Add this as a recipe in an account at insight-live.com (and assign it a code number to write on all test specimens) to start a testing project. Along the way document it with pictures, firing schedules, general notes, etc.
-With all that feldspar, it is sure to craze, reducing the high thermal expansion K2O it contributes in favor of low expansion MgO (from talc) is the first fix to try.
-With all that clay (29 total) it is likely to crack while drying (and then crawl during firing). Try reducing shrinkage with 29 kaolin (no ball clay). If it still cracks, substitute some for calcined kaolin.
-And those colorants: It is better to use cobalt oxide than carbonate. A burnt umber increase could be tested to eliminate the need for both the manganese and iron (since it supplies both and has zero LOI). Better yet, remove all four and use a black stain (7% would likely be enough).
-Perhaps the best option is to get a different glaze recipe. This is a calcium matte to G1214Z1 would be a good start. For a more pleasant surface, G2934.

Pages that reference this post in the Digitalfire Reference Library:

Calcined Kaolin, Are your glaze recipes lost in binders or buried on your phone?, Tuning the degree of gloss on a matte black glaze, Make your own black glaze. How?, Two cone 6 black glaze recipes I control and adjust A gloss and a matte based on two reliable base recipes, GLC - Glaze Chemistry

This post is one of thousands found in the Digitalfire Reference Database. Most are part of a timeline maintained by Tony Hansen. You can search that timeline on the home page of digitalfire.com.