Modification Date: 2016-03-20 23:51:42
Gerstley Borate substitute
This material was developed by Plainsman Clays as a substitute for Gerstley Borate. Boraq 1 was later adjusted to become Boraq 2 (recipe also available).
The materials in the recipe are difficult to get in most places. Actually, Cadycal and F-4 Feldspar are no longer manufactured. However we make this and other recipes public as examples of how material substitutes can be formulated to emulate the physics and chemistry of others.
For more information about the logic behind this recipe and why it was adjusted to Boraq II please visit the Boraq material page at digitalfire.com.
Floating Blue is a popular cone 6 glaze recipe used by the pottery community. Gerstley Borate is a material commonly used in recipes as a melter. The recipe produces a variegated surface but is difficult to replicate since its fragile mechanism makes it susceptible to variations in thickness, firing schedule, clay body and material supplies.
The rutile blue variegation effect is fragile. It needs the right melt fluidity, the right chemistry and the right cooling (during firing). This is Alberta Slip GA6C recipe on the right (normal), the glaze melt flows well due to a 20% addition of Ferro Frit 3134 (a very low melting glass). On the left Boraq has been used as the flux (it is a calcium borate and also melts low, but not as low as the frit). It also contains significant MgO. These two factors have destroyed the rutile blue effect!
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2016-03-20 - Boraq 2 was derived from Boraq 1 in response to issues with matching Gerstley Borate better in higher temperature glaze recipes. Please visit the Bora...
By Tony Hansen+