There are different types of wood finishes and most of them don’t work together so if you need to touch up a finish, how do you identify what the finish is?

You can test the finish in a specific sequence. The first type of finish to test is oil. The main types of oil finishes are Boiled Linseed oil, Tung oil, and Danish oil. Any of these are compatible with each other and its easy to identify an oil finish. Put a drop of oil on the finish and let it sit for a few minutes. If it absorbs into the wood, it’s an oil finish. If it doesn’t, you have a shellac, lacquer, or poly/varnish type of finish.

Another hint to identify the finish is the furniture itself. Oil finishes are more common on fine furniture and mid-century modern furniture, so consider the piece you working on. If you see the grain of the wood in the surface of the finish instead of a solid film, it’s likely an oil finish.

If you’ve done the oil test on your piece, and it’s not an oil finish, the next thing to test for is a shellac finish. It’s important you test your finish in this order to determine what it is because some solvents work on multiple finishes.

To test for a shellac finish, you need to use a drop of denatured alcohol. Let it sit for a a few minutes, then try to dab it up with a rag or paper towel. If the surface is sticky and mushy, it’s a shellac finish. Shellac finishes are common on antiques, so that’s a hint when you look at the furniture.

The third test is to see if the finish is a lacquer. Lacquer is a common modern finish because it dries quickly, which means less chance for dust to settle on it and a higher rate of production in manufacturing. It’s not a common DIY finish because it is very toxic and usually applied with spray equipment.
To identify a lacquer finish, you need to place a drop of lacquer thinner on the piece. After about 20 seconds, dab it with a rag or paper towel to see if it’s sticky. If it is, you have a lacquer finish. If it isn’t, you have a polyurethane or varnish finish.

A polyurethane or varnish finish forms a protective plastic film. You need some very strong chemicals to soften the finish, which is why I suggest testing in the order of oil, then shellac, and then lacquer. By process of elimination, if nothing softens the finish, it’s polyurethane or varnish. Polyurethane and varnish will chip where the other finishes typically won’t.

How do you repair these finishes? Repairing an oil finish is simple. Just apply a new coat of oil.

Repairing a shellac finish is also easy, it’s just a matter of cleaning off the surface with warm water and a mild detergent such as dish soap, and then applying a new coat of shellac.

To repair a lacquer finish, I clean the surface with mineral spirits to remove any oil or grease. I show how to repair a lacquer finish in a separate video - [ Ссылка ]

To repair a polyurethane or varnish finish, the new coat of finish sits on top, so it needs something to grab on to. Sand the old finish with 400 grit sandpaper to rough up the surface and then apply a new coat. I show how to repair a polyurethane finish as part of a Windsor chair restoration in this video - [ Ссылка ]

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