On paper, Fusion F-19 has a very similar chemistry to 3124. However, as can be seen here, it is flowing a little more and appears to have a lower surface tension. The glass is also more transparent and the entrained bubbles are bigger. The differences could be partly to Fusion using a different set of raw materials to source the chemistry or differences in their smelting process.
The Fusion one is flowing a little more. And it has larger bubbles, so Fusion must be using a different set of raw materials to source the chemistry (materials that either have higher LOI or decompose to produce gases later in the firing). They do not supply the chemistry of Frit F621/19 and it is not shown on their website in 2021. But they recommended it to us as substitute candidate for Ferro Frit 3124.
|Materials||Ferro Frit 3124|
|Materials||Fusion Frit F-19|