In March, I wrote about my experiences with reactive red glass powder and a particular project that I was salvaging from a previous "learning experience" (see Positive Reactions). The reaction between the compounds in two pieces of glass (for instance, sulfur and copper) cause a distinct outline where the two pieces meet. The reaction adds a lot of depth and dimension to the glass that is hard to achieve using other methods.
Both of the two major fused glass suppliers publish information on their reactive glasses. You can find Bullseye Glass's reactive chart here and Spectrum's System 96 reactive red chart here.
While you're visiting these sites, don't forget to take a look around. Both manufacturers generously provide a wealth of information on their web sites, including firing schedules, kiln forming and cold working techniques, and project ideas.
Bullseye Glass Educational Videos