I have just used the last of my G-200. I have seen several suggestions for a substitute but would like everyone's opinion. Thanks!
If the recipe melts with G200 then use Custer or minspar. Neph sy is a soda spar, G200 is more a potassium spar. Compare materials to keep the recipe the same, not whether something melts earlier. I think I would pick (my opinion) Custer, then minspar and very last neph sy just rough comparing which are most similar in chemical composition.