Luthier Tips du Jour Mailbag - Determining Finish Type

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In this episode, luthier and instructor Robbie O'Brien demonstrates how to determine the type of finish on a guitar.

Video Transcription

[on-screen text reads: Luthier Tips du Jour Mailbag]

Mailbag question: Is there a way to know what type of finish is on my guitar?

Robert O'Brien: Today's tip to your question comes to us from Washington.

"Dear Robert, I would like to know what type of finish is on my guitar. Is there a way to determine this? Thank you for the videos, Mark in Washington."

Mark, it's very important to know what kind of finish is on your guitar, especially if you have to do finish work or you have to do repair work. You need to know what kind of finish is on that guitar.

Knowing the manufacturer and period of the instrument

Now, sometimes it's very easy to know. For example, the period of the instrument. If it's pre 1920 era, then probably it's done in a shellac finish. Now, you don't know what's been done along the way as well, so that could be a problem. But pre 1920 or thereabouts, probably was finished in shellac. Then, anything after that started coming into the lacquers. As we progressed through the years, through the decades, then we started with the modern day resins like the catalyzed urethanes and the polyesters and things like that.

Knowing the era or the period of the instrument, sometimes it's just a dead giveaway. But like I said, somebody's probably done something along the way and there could be several types of finishes on your guitar.

Also knowing the manufacturer. Sometimes it's Gibson or Martin or whoever used different finishes in different years. So that's another way to find out. You can call the manufacturer or you can do some research about what type of finish was used on that time period for those guitars.

A simple acetone test

Now, I'm going to show you a simple test that will allow you to discover what kind of finish you have on your instrument. So Mark, to discover what kind of finish you have on your instrument, I'm going to use acetone. I'm going to place a small amount on a Q-tip, emphasis on the small amount, and then I'm going to rub this on an inconspicuous area of the guitar. Sometimes you can remove a tuner or some area that's not going to be seen.

On this instrument, I'm going to rub it just right back here on the small amount of the binding. Now, if this were lacquer, that would leave a permanent mark. It would melt that finish and leave a permanent mark where I'm rubbing the acetone. And it's not doing that. Since the acetone on the Q-tip is not leaving a mark on this finish, this tells me that this is probably some type of catalyzed product, either a urethane or a polyester or some type of catalyzed polymer. It's not leaving a mark at all. If this were a shellac finish, then if I did that, it would slowly start to melt the finish and it would leave a small mark there that I could easily touch up with some shellac. So it's not lacquer, it's not shellac. This one is probably a catalyzed, my guess is probably a urethane.

With that information, I can now proceed to do whatever I need to do to the guitar, repair it or refinish it.

Mark in Washington, thank you very much for your question. I hope you find this information useful. However, if you're going to tackle refinishing your own instrument, I highly recommend that you seek out a qualified professional or really do your research, because refinishing an instrument can really turn into a bucket of worms in a hurry. Happy finishing.

[on-screen text reads: More Luthier Tips and online courses available at www.obrienguitars.com]

StewMac

 

Robbie O'Brien

Luthier and Instructor, Lutherie Academy