Full fuse: Two layers of
Full fuse: Two layers of glass with additional decorative pieces on top OR one layer of glass mostly covered with decorative pieces comes out flat (1/4″ thick)
Soft fuse: Also called a “dimensional fuse”. Decorative pieces do not fully fuse into base layer. Edges and corners are significantly rounded.
Tack fuse: Everything looks pretty much like it looked when it went in — only stuck together. Sharp edges and sandblasted surfaces are fire polished smooth and glossy.
Keep in mind that there are an infinite number of places you can stop between tack and full fuse and nobody can say with authority where tack fuse ends and soft fuse begins — or where soft fuse ends and full fuse begins. Moreover, a firing schedule that tack fuses a piece of white glass may soft fuse a piece of black — because every glass has its own melting temperature.
My advice is not to get hung up on the mostly arbitrary names — focus on the results that you want and test in your own kiln to see what temperature and hold time give you those results.
Helios Kiln Glass Studio