A down side of high feldspar glazes: Crazing!

Wednesday 16th October 2013

This reduction celadon is crazing. Why? High feldspar. Feldspar supplies the oxides K2O and Na2O, they contribute to brilliant gloss and great color (at all temperatures) but the price is very high thermal expansion. Any glaze having 40% or more feldspar should turn on a red light! Thousands of recipes being traded online are high-feldspar, some more than 50%! There are ways to tolerate the high expansion of KNaO, but the vast majority are crazing on all but high quartz bodies. Crazing is a plague for potters. Ware strength suffers dramatically, pieces leak, the glaze harbours bacteria, crazing invites customers to return pieces. The fix: A transparent base that fits your ware. Add colorants and opacifiers to that. Another fix: substitute some of the KNaO for a lower expansion flux (like MgO, SrO, CaO, Li2O) and add as much SiO2 and Al2O3 as the glaze will take (using glaze chemistry software).

Pages that reference this post in the Digitalfire Reference Database:

Na2O, Crazing, Celadon Glaze, Calculated Thermal Expansion, Glaze Crazing

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.