Vegetable-tanned leather smooths best by burnishing. Trim the edge flat, bevel the corners, sand through progressively finer grits, dampen the edge, then rub it with friction until the fibers compress and seal. Chrome-tanned and soft leathers do not burnish well, so they are finished with edge paint instead.
Check the leather first
Leather is often sorted into grades such as full-grain, top-grain and “genuine” leather. The grade affects the surface, but the tanning matters most for edges. Vegetable-tanned leather burnishes. Chrome-tanned leather generally does not.
Thickness matters too. Thicker, firmer leather (over about 3 mm) burnishes more easily than thin, soft leather.
If you are not sure of the tanning, use the drop-of-water test. Veg-tan soaks in and darkens. Finished chrome-tan tends to bead. Test a scrap, since results vary.
Trim and level the edge
Start with the layers trimmed flush. Glue lines and uneven layers show up as steps along the edge, and burnishing cannot fix a step. Level the edge with a sharp knife or an edge plane, or sand it flat on a block. The goal is one continuous surface.
If you plan to bevel and stitch, bevel before stitching where you can, so the beveler does not catch the stitches.
Bevel the corners
Use an edge beveler to shave the sharp 90-degree corners on both the grain side and the flesh side. Beveler sizes are numbered, commonly #0 to #4. A #1 or #2 suits most 2 to 4 mm leather.
A bigger beveler does not give a smoother edge. An oversized beveler just leaves a thin, rounded edge.
Beveling without a special tool
You can soften the corners without a beveler. Wrap fine sandpaper around a block and rub the corners until they round over. A sharp craft knife can also shave a corner at a shallow angle, but it is easy to cut unevenly, so practice on scraps first. Both methods are slower and less even than a beveler.
Sand through the grits
Sand the edge in progressive grits, for example 220, then 400, then 600 or finer. If the edge is uneven, start coarser, around 120 to 220, to level it. Sanding does the leveling work. Burnishing only refines the surface.
Wear a dust mask when sanding, and take extra care with dyed or painted edges.
Dye the edge (optional)
If you want color, apply edge dye after sanding and before the final burnish. Let it dry completely before moving on. For help choosing a dye type, see water-based vs alcohol leather dye.
What burnishing is and how to do it
Burnishing smooths the edge with friction. You dampen the edge, then rub it back and forth with a smooth tool until the fibers compress into a smooth, sealed surface. The heat from the friction helps set the fibers.
Choose a burnishing agent
Water is the simplest choice. Gum tragacanth, Tokonole and saddle soap are common alternatives. Use only a light dampening. A soaked edge goes fuzzy and swells, so more water is not better.
Burnish with friction
Use a hardwood slicker, a canvas cloth or denim. A slicker in a drill or rotary tool can speed the job. Use firm pressure and fast strokes, and stop before the edge scorches. Repeat the cycle two or three times: dampen, burnish, let dry.
Power slickers can grab the work, so keep your fingers clear and run them at a moderate speed.
Wax and buff
Finish with beeswax or paraffin rubbed along the edge, then buff with a dry canvas or nylon cloth to bring up a soft shine.
Oiling the flesh side of the piece is a separate question. If that is what you are asking, see should you oil the rough side of leather.
Edge paint for chrome-tan and soft leather
Chrome-tan, oil-tan and bonded leathers do not burnish with friction and water. They usually get edge paint. Sand the edge smooth first, then apply thin layers of a flexible edge paint such as Fenice or Giardini, with a light sanding between dry coats. Expect about 3 to 5 coats. Edge paint is the standard finish for chrome-tan, not a cheap shortcut.
For painting in general, see can you paint leather.
Common mistakes
- Too much water. A soaked edge goes fuzzy and swells.
- Expecting burnishing to fix a stepped edge. Sanding does the leveling.
- Using an oversized beveler. It leaves a thin, rounded edge, not a smoother one.
- Treating edge paint as a shortcut. It takes several thin coats.
Safety
Power-tool slickers can grab the work. Keep your fingers clear and use a moderate speed. Wear a dust mask when sanding, especially dyed or painted edges.