shabba zabba Posted November 14, 2010 Report Share Posted November 14, 2010 Brierly's White is a very reliable glaze in my studio. It has been used for years in our gas kiln. Two or three firings ago hundreds of dollars of pots were lost when this old reliable glaze shivered! Immediately we thought it was the minspar which is being tested as a replacement for f-4. I then came upon an old bag of f-4 and so mixed another batch of the glaze w/ the f-4, just to get us through the next firing while we were still testing the minspar w/ out glazes... brierly's shivered again! does anyone have any ideas what other ingredient may have caused this? thanks! Link to comment Share on other sites More sharing options...
Ben Posted November 14, 2010 Report Share Posted November 14, 2010 Brierly's White is a very reliable glaze in my studio. It has been used for years in our gas kiln. Two or three firings ago hundreds of dollars of pots were lost when this old reliable glaze shivered! Immediately we thought it was the minspar which is being tested as a replacement for f-4. I then came upon an old bag of f-4 and so mixed another batch of the glaze w/ the f-4, just to get us through the next firing while we were still testing the minspar w/ out glazes... brierly's shivered again! does anyone have any ideas what other ingredient may have caused this? thanks! If the glaze was mixed properly, with known good ingredients from the same bags as the last batch as you say it was, the only other variables are the clay body and the firing. I'd say the easiest thing to test would be the clay body. What temp do you fire to and do you have some of this same batch of clay available to make some tests? It is possible to use a series of glazes with gradually increasing coefficients of expansion to test a clay body. I learned this from "Mastering cone 6 glazes" (Great book BTW) Anyway, use these glazes and see how each fits the fired sample. That will tell you the approximate COE of your clay body. If the clay body is to blame, this test will show it. Here is a series of glazes for cone 10 that work very well for me testing clay bodies fired to cone 10 in reduction. #0 ====== CUSTER FELDSPAR..... 66.50 66.50% WHITING............. 21.00 21.00% Silica.............. 9.50 9.50% EPK................. 3.00 3.00% ======== 100.00 EXPAN649.97 #1 ====================== CUSTER FELDSPAR..... 62.00 62.00% WHITING............. 18.50 18.50% Silica.............. 13.00 13.00% EPK................. 6.50 6.50% ======== 100.00 EXPAN597.88 #2 ================ CUSTER SPAR......... 530.00 53.00% WHITING............. 183.00 18.30% EPK................. 118.00 11.80% Silica.............. 169.00 16.90% ======== 1000.00 EXPAN550.38 #3 ================ CUSTER SPAR......... 471.00 47.10% WHITING............. 153.00 15.30% EPK................. 149.00 14.90% Silica.............. 175.00 17.50% Talc................ 52.00 5.20% ======== 1000.00 EXPAN501.03 #4 ================ CUSTER SPAR......... 396.00 39.60% WHITING............. 134.00 13.40% Talc................ 83.00 8.30% EPK................. 186.00 18.60% Silica.............. 201.00 20.10% ======== 1000.00 EXPAN449.72 #5 ================ CUSTER SPAR......... 375.00 37.50% WHITING............. 71.00 7.10% Talc................ 183.00 18.30% EPK................. 203.00 20.30% Silica.............. 168.00 16.80% ======== 1000.00 EXPAN399.94 #6 ================ CUSTER SPAR......... 250.00 25.00% WHITING............. 100.00 10.00% TALC................ 150.00 15.00% SILICA.............. 250.00 25.00% CAL KAOLIN.......... 125.00 12.50% EPK................. 125.00 12.50% ======== 1000.00 EXPAN350.54 Link to comment Share on other sites More sharing options...
Marcia Selsor Posted November 14, 2010 Report Share Posted November 14, 2010 Are you using the same clay? Shivering usually is caused by an ill fitting glaze. If the glaze is the same..did the clay body change? What is the recipe? What are the clay bodies being used. Did all the clay bodies have the shivering problem? Is the firing the same? Marcia Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.