Melt fluidity test showing Perkins Studio clear recipe original (left) and a reformulated version that sources the boron from Ferro Frit 3134 instead of Gerstley Borate (right). The later is less amber in color (indicating less iron) and it melts to very close to the same degree.
Pages that reference this post in the Digitalfire Reference Library:
Gerstley Borate, B2O3, G2926B - Cone 6 Whiteware/Porcelain Transparent Base Glaze, A Low Cost Tester of Glaze Melt Fluidity, Trafficking in Glaze Recipes, Find and Improve a Cone 6 Clear Ceramic Glaze
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.