This calcium borosilicate glass is made by Fusion Ceramics. It is a very close substitute for Vibrantz frit 3124 formerly made by Ferro. It makes a good cone 04 glaze with the addition of 10% EPK and a good cone 6 clear with 15% EPK and 10% silica.
First fusion: 1550ºF / 871ºC. cte: 7.90 x 10-6
For more information on frit F-19, see the Digitalfire.com Reference Library of ceramic materials.