This calcium borosilicate glass is made by Fusion Ceramics. It is a very close substitute for Vibrantz frit 3134 formerly made by Ferro. F-12 frit initiates early melting (like Gillespie borate) promoting fuller fusion of other glaze ingredients. With the addition of enough siliceous clay, the chemistry of F-12 is very similar to frit F-19.
First fusion: 1450ºF / 788ºC. cte: 8.18 x 10-6.
For more information on frit F-12, see the Digitalfire.com Reference Library of ceramic materials.