Basic Questions about Finishing Products

[Pat Germain]

I can't find a finishing FAQ. Therefore, I'm hoping it's OK to post a few basic questions about finishing products. I started to do woodworking back in the 80's, but I haven't been able to do much with wood for a very long time. I'm recently getting back into it. My information about finishes was never very complete and I fear is also now dated.

- Shellac: Call me crazy, but I was under the impression that shellac is actually "catterpillar poop" dissolved in a solvent. Perhaps I'm confusing it with something else, but I recall that shellac provides an extremely high gloss, but is not waterproof. So, is it practical as a furniture finish? Or, am I just out to lunch here?

- Tung Oil: What exactly is this stuff? I've seen it used on woodworking shows and I really like the look. How practical is it? Is it difficult to use or prohibitively expensive?

- Linseed Oil: This stuff seems to be some kind of magic, voodoo elixer. In what circumstances does linseed oil work best? I've actually used it many years ago on a teak entertainment center I own. I really wasn't impressed, but it's likely I didn't apply it correctly. I avoided linseed oil mostly because of all the dangers I've read about this stuff spontaneously combusting on rags and such. Is this true, or just hype?

Thanks.

[Howard Acheson]

I can't find a finishing FAQ. Therefore, I'm hoping it's OK to post a few basic questions about finishing products. I started to do woodworking back in the 80's, but I haven't been able to do much with wood for a very long time. I'm recently getting back into it. My information about finishes was never very complete and I fear is also now dated.

- Shellac: Call me crazy, but I was under the impression that shellac is actually "catterpillar poop" dissolved in a solvent. Perhaps I'm confusing it with something else, but I recall that shellac provides an extremely high gloss, but is not waterproof. So, is it practical as a furniture finish? Or, am I just out to lunch here?

- Tung Oil: What exactly is this stuff? I've seen it used on woodworking shows and I really like the look. How practical is it? Is it difficult to use or prohibitively expensive?

- Linseed Oil: This stuff seems to be some kind of magic, voodoo elixer. In what circumstances does linseed oil work best? I've actually used it many years ago on a teak entertainment center I own. I really wasn't impressed, but it's likely I didn't apply it correctly. I avoided linseed oil mostly because of all the dangers I've read about this stuff spontaneously combusting on rags and such. Is this true, or just hype?

Thanks.


First, let me suggest you get either Bob Flexner's Understanding Wood Finishing or Jeff Jewitt's Taunton Complete Illustrated Guide to Finishing. Either, or both, will give you all the info you need to understand products and then how to apply them.

Shellac is obtained from the secretion of the female insect found in India. It is refined and dried. It is then re-liquified by dissolving it in alcohol. It makes an excellent furniture finish and was the preferred finish until the development of lacquer finishes after WWI. It is not waterproof if water is left standing on it. If the water is wiped off in an hour or so, no damage will result. While not really water resistant, shellac is the most water vapor resistant finish. Use for the correct applicationd, shellac is an excellent finish. It is used extensively as a sort of sealer/primer and as a barrier coat between incompatable finishes.

Tung Oil is a drying oil made from the nuts of the tung tree. It is little different from linseed oil. Tung oil is slightly less yellow and slightly more water resistant although neither tung oil or linseed is very water resistant at all. Neither makes a good stand alone finish and are best used to pop the grain and/or for coloring. For any real protection, they both must be overcoated with a protective finish. If you are referring to David Marks as one who used "tung oil" let me direct you to his website. He explains there that he uses General Finishes Arm R Seal. This is a urethane wiping varnish material and contains no tung oil at all. On newer shows he does not call it "tung oil". A wiping varnish is much more protective than a tung oil. Most products labeled "Tung Oil Finish" contain linseed oil and no tung oil.

Linseed oil is an oil produced by flax seeds. You can get ether raw linseed oil or boiled linseed oil. Raw linseed oil is used primarily to make varnish and paint. BLO contains metallic driers to speed the curing of the oil. Tung oil is very slow curing (7-20 days) while BLO cures in about 2-3 days. See the above dialogue about "tung oil". There is little difference between the two oils. Neither are a good finish. BLO produces heat as it cures. Rags wadded up and put into an enclosed space can get hot enough to ignite. They should be spread out flat or hung on a line until they dry. Then they can be safely discarded.

[Pat Germain]

^^ Very informative. Thanks, Howard.

I have indeed seen David Marks refer to his finish a "tung oil". I went to his web site previously and was confused because he doesn't use that term there.

Although it's rare, I have also seen Norm use tung oil. It may have been back in the late 80's when the show first started, but he did use it.

I'll look into the finishing books. Thanks for the recommendation.

[Joe Chritz]

Just to make it more confusing not all Tung oil's are tung oil.

Some are a wiping varnish with a little tung oil in it. True tung oil is a drying oil similar to linseed oil without any darkening properties. Several brands of "Tung oil finish" is a wiping varnish.

Wipe on poly is a wiping varnish with a urethane resin. Waterlox is a wiping varnish with phenolic as a resin. They may have other things as well.

The best thing you can do, which is advice I have gotten from here and other places is to grab some different stuff and do some test pieces. Track sanding, stains and finishes to see what it looks like.

The books are a really good idea.

Joe