Broken glass is usually a bad thing, but when it comes to shoe making a well broken piece of glass can be the making of a smooth sole edge, sole or heel. It is a vital part of finishing.
Whilst rasping the edges blends the layers of leather together to make one surface, glassing then smooths that surface, before sanding with the differing grades of sandpaper.
Picture frame glass is ideal - not too thick and not too thin - and we keep a ready supply in a sturdy box in the studio. The ideal thickness of glass is 2-3mm because it breaks cleanly. Any thinner and you're likely to get more shards and any thicker and breaking it is more difficult with less clean results.
Use another piece of glass or a file to nick or chip the edge of the glass (make a small dent in the edge).
Rest the edge of glass with the dent in it on a sharp edge such as the edge of your work table or burner. Position the nick so that it is right on the sharp edge. Lean the glass forward at about 45 degrees.
Press gently forward and down with your thumbs, slightly rotating your wrists outwards.
This should take very little effort. Do not force it. If it does not break first time, then adjust the angle of the glass slightly or nick it again. The gentle pressure from your thumbs should break the glass into two pieces, one with a convex edge and with with a concave edge.
It is the outwardly curved convex edge that we use to scrape edges and soles.
And in case any of you are wondering how the hammered boots from the last two posts turned out....here they are finished!
Until next week, happy shoe making!