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I'll use my razor blade scraping trick to level this lump of very brittle finish:
First, I draw a bur on the blade:
Then tape the ends so I don't scratch the surrounding finish:
And scrape the shellac lump almost down to the surface:
Here you can see the lump of shellac appears almost like a transparent smear:
I've scraped the lump so close to the finish that there's only about 0.002" protruding above.
From here I need to do just a tiny amount of block sanding to level the filled area to the surrounding finish, and I can polish the surface:
Stick shellac is obviously the ideal fill for a shellac finish, because it's the same stuff. It also works perfectly with varnish finishes. Stick shellac needs no time to dry because there are no solvents to evaporate, so the filled area is completely cured the moment it cools.
This mandolin is featured in the French polish article. I filled the largest of the holes in the face with stick shellac before applying the new shellac coats in the French polish method.
Under shellac French polish, the stick shellac filled areas are a seamless part of the finish. Large stick shellac fills should not be used under lacquer finish because the lacquer causes the stick shellac to soften and remain pliable for months, at least.
Like many of the "obsolete" techniques, French polishing and stick shellac require practice to master. I believe that as restorers, we should work with the materials and techniques used when the instrument was built.
The old time techniques are neither lost nor mysterious. We can learn them. After all, thousands of craftsmen did this stuff every day only a few decades ago throughout the woodworking industry. No reason we can't learn to be efficient working this way, too!
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