We use broken glass bottles...blue and green work well...and the blue and green half marbles for covering the surface of planters. I require a border of some sort to contain the flowing glass, horizontal surfaces only. As they are decorative I suggest inside knobs, carved soap dishes and candle holders or flatish lids with chanels trimmed or carved.
Fluid glazes seem to be better than stiff glazes. If using other colours of glass which tend to become clear then using a coloured glazes work nicely. Our favourite glaze is Randy's Oatmeal Rust.
The better types glass are the rods used by glas