A neutral flame is hotter than either a reducing flame (more propane than oxygen) or an oxidizing flame (more oxygen than propane). Does that answer your question?
A reducing flame will tend to bring metals to the surface in some glass, giving them a metallic or iridescent surface. Not all glass will react this way. Few of the Effetre colors react to a reducing flame except in a bad way. Rubino turns gray. The greens and turquoises (primarily the opaques) will get brick-red streaks if exposed to enough of a reducing flame. That's the copper coming out. A heavily reducing flame makes the glass get dirty and sooty. To some extent, putting the glass back in a neutral or oxidizing flame can clean it up. An oxidizing flame doesn't usually have much of an effect on soft glass, except for silver plum and dark silver plum, where it brings out the colors.
For most (but not all) of the silver colors, such as the 104 COE glass made by R4 (Precision 104) and Double Helix, you want to put the glass in a reduction flame. Some of the colors are not reduction colors, though, so look at the tips for working each particular color before you start working with it.
In soft glass, the colors that go strongly metallic in a reducing flame are in the 94-96 COE range. There are some made by Kugler and by Reichenbach. I'm not sure who else makes reducing colors. You can use small quantities of these glasses with 104 COE glass as frit or as stringer decoration, although if you leave any decoration raised you have to make very sure that it is well attached, because it's particularly likely to want to pop off. Bullseye has some luster colors that look like reduction glass, although I'm not a Bullseye user so I don't know if these colors are actually used in a reduction flame or not.
Flame chemistry is much more important for boro than it is for soft glass. If you're working boro, you'll want to read up on each individual color you're using to get some suggestions on how to work it, and then you'll want to experiment from there. Glass Alchemy and Northstar have good manuals and tips on their websites that provide a good starting place.
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