PottaFella Posted December 2, 2016 Report Share Posted December 2, 2016 A friend has a number of mixed glazes for 1280c (with soak this works out at about cone 10), is there something that could be added to reduce their firing temp towards cone 6? If not possible, longer term, would swapping the Potash Feldspar with Potash Soda Soda Feldspar likely reduce its firing temp? The type of glaze we are dealing with is: Pot Feldspar 50 China Clay 22.5 Dolomite 22.5 Whiting 5 + various oxides depending on colour Link to comment Share on other sites More sharing options...
Marcia Selsor Posted December 2, 2016 Report Share Posted December 2, 2016 The easiest way is ti start by adding 10% gerstley borate. Adjust from there. Marcia Link to comment Share on other sites More sharing options...
Dick White Posted December 2, 2016 Report Share Posted December 2, 2016 Some key differences between cone 6 and cone 10 glazes include: Boron is a glass former that melts at a significantly lower temperature than silica, and so is used as if it is a flux. The silica and alumina levels (as measured by molar parts) are slightly lower. And there is a tilt towards the alkaline fluxes rather than the alkaline earths, together with a tilt towards sodium as a more powerful flux vs. potassium, and some usage of lithium. There is no single magical material that instantly cause a cone 10 glaze to turn into a cone 6 glaze. Glaze materials tend to be complex, each causing multiple changes in a glaze composition. Gerstley Borate, as Marcia suggests, is a boron source. Sometimes nepheline syenite can be substituted for a feldspar to bring more sodium flux into the glaze. Sometimes a few percent of lithium carbonate can be added for additional fluxing. Sometimes a few percent of kaolin or ball clay can be removed to slightly reduce the silica and alumina to cone 6 levels. But all these ideas require testing and adjustment, as Marcia noted. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted December 2, 2016 Report Share Posted December 2, 2016 I have used NS as well. But "colemanite" which then was substituted by gerstley borate was a common way to change a ^10 to ^6 back in the 70s. Marcia Link to comment Share on other sites More sharing options...
neilestrick Posted December 2, 2016 Report Share Posted December 2, 2016 Some glazes will drop to 6 with as little at 4% Gerstley. Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted December 2, 2016 Report Share Posted December 2, 2016 I tried using colemanite once and it jumped off the pots. Calcium borate frit is about the same price as GB and I prefer that. Link to comment Share on other sites More sharing options...
glazenerd Posted December 3, 2016 Report Share Posted December 3, 2016 I am rather fond of my Calcium Borate. 52% boron 38% calcium. GB 27% boron 19% calcium. Nerd Link to comment Share on other sites More sharing options...
Marcia Selsor Posted December 3, 2016 Report Share Posted December 3, 2016 Here is an example of a glaze I converted to ^6 from ^10 back in 1980 when we moved to a new facility and I decided to convert to ^6 to reduce costs. When you add 10% to 100 , it becomes 9% when the total is back to 100. SELSOR Semi matt ^6 Reduction EPK 20.3 Dolomite 17.7 Neph. Syen. 33.6 Silica 15.9 Whiting 3.5 Ger, Borate 9 100 Takes colors well Blue/lavender 1% cobalt Carb Light green 1.5% Nickel Carb 1.5% Rutile Lt. Blue gray .5% cobalt carb. 2.5% rutile gray 2.5 rutile +2.5 nickel carb. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.