process of finishing the edges of outsoles, any midsoles, and shoe heels
Makers and shoe companies vary a lot in how they go about this, but often just in details: what kind of abrasive to use for a particular grit, whether or how much they wet before abrading, and whether they add liquid products like hardeners, gums, varnishes, or lacquers. The overall outline of the process is usually consistent, with particular steps omitted, simplified, or made more intricate, depending on the intended level of finish polish. In general terms, it’s not unlike the process of finishing the top of a fancy wood table.
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Trim the rands and lifts with knives.
This avoids wasting time cutting the waste away with slower abrasive tools.
Leave whatever excess is necessary to avoid unintentionally cutting away too much.
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Prepare the surface for sanding.
Some makers compress the fibers from the edge by hammering, peening, or pressing.
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Smooth the heel stack with progressively finer abrasives.
Coarse abrasives include rasps, files, and coarse sandpapers or emory papers. Medium abrasives include shards of glass and medium sandpapers or emory papers. In modern practice, fine abrasives are nearly always fine sandpapers.
Sandpapers and emory papers may or be rubbed by hand, fixed to sticks or blacks used by hand, or mounted in finishing machines.
Hardeners, gums, varnishes, and lacquers are commonly applied during this process, often after glassing or medium sanding and before high-grit sanding. Following a hardener that only penetrates shallowly with too much work by a coarse abrasive may simply waste the abrasive and take off all the hardener. On the other hand, applying hardener and removing all but a thin surface film can produce very fine gloss effects.
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Burnish the abraded surface.
This is often done with iron tools like glazing irons, burnisher irons, heel irons, edge irons, and so on, often heated. It may also be done with wood or bone burnishing stick. Some also use very fine abrasives on buffing wheels.
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Wax.
Makers vary in the kinds and hardnesses of waxes they apply. They also vary in how they apply them.
Some rub wax directly onto heels and edges, like crayons. Others ruby a bit of wax onto the surface, then spread it with a cold or heated tool.
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Burnish the wax.
This is most often done with heated irons or soft wheels on finishing machines.
When edges are dyed as well, dyes may be applied at one or multiple points in the process, often after trimming or abrading. Water-based dyes affect the moisture of the leather, and therefore interplay with choices and progressions of abrasives.