Stick Shellac
© Frank Ford, 3/27/98; Photos by FF, 5/4/95
Shellac is a natural resin we use in liquid form dissolved in alcohol. It's also useful in the solid state because it can be melted and used to fill nicks and voids in finishes. (Sealing wax is opaque colored shellac.)
Shellac for melting is generally known as "stick shellac" because it's made up as little bars for easy handling. This solid shellac comes in its natural very dark amber color, refined to lighter shades of transparent amber, or opaque, mixed with pigments in every imaginable color:
Most of the time, I work with transparent finishes and I use the amber shades, like the light amber one I'm holding.
The process of melting solid stick shellac into a finish is known as "burning-in." Hence, the sticks are frequently called burn-in sticks, and the hot knife used in the process, a burn-in knife.
Burn-in knives may be any sort of heated blade, but the most popular one is mounted with an electric element like a soldering iron:
Here I'm using the burn-in knife to carve off a small piece of medium amber stick shellac to use in filling these holes in the face of this 1919 Gibson A-2 mandolin:
I get a bit of the stick shellac melted on the tip of the blade, and press it into the wound in the finish.
Sometimes the stick shellac gets hot enough to bubble as I'm pressing it down. I've found that I can squish the bubbles and improve adhesion if I take the knife off the surface and immediately mash down the shellac with my finger.
It was tough to get a shot of this, but here's a big lump of shellac I've burned into the finish:
It completely fills the holes, and stands high above the finish, covering a big area compared to the size of the holes.
My task is then to carve the lump down to the surface, so that the only remaining stick shellac is that which went down into the holes.
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