A number of my students have experimented with adding glass to their work at cone 6 electric.
First, unless you are firing to VERY low cones, most common glass will melt entirely and flow to the lowest point it can reach. Experiment only on the interiors of test pots first...unless you want to replace kiln shelves for the studio....
Second, less is often more. Experiment by beginning with small quantities of glass (just enough to cover the bottom of a piece), then increase to gauge results.
Third, real glass beads from the craft store are another source to explore. But they are very light and roll around. If you use glass that can roll, it is helpful to glue it in place to make it easier for the person loading the kiln. Just regular glue, like Elmer's, which will burn off long before anything starts melting...not an option to hold the glass where you want it for the entire firing.