At 1700F the fast fire frits show an important difference
These were 10g balls melted using our GBMF test, the tile they are being fired on is a groggedstoneware clay. A few of the more interesting ones here are frit 3470 lead zinc, 3185 super high boron, CC257 high barium, FR003 high alkali and F49 and FR001 opacifieds. Notice how early and vigorously some are melting. But notice 557 and 556, they aren’t doing anything - that is not by accident. These are fast-fire frits, they are designed to melt later and more quickly. This is only 1700F, since no one fires this low it makes sense that if a glaze has not started melting it will be able to pass escaping gases of decomposition. This avoids the bubbles and surface defects these cause, as 3185, CC257 and 3470 are already demonstrating. What about FR002, FR002 and 3565, they are melting and look fine? They have higher surface tension and much less contact with the body generating the gases.