Saturday, June 9, 2012

Pure Gum Turpentine vs. Turpenoid

     Unless you have a bit of scientific curiosity and like to experiment with different ways to finish wood, this blog may not be too interesting to you!  You've been warned but I'd encourage you to read on because I found this quite fascinating.  I'm scheduled to do a show this September at the Urban Ranch General Store which will be of a series of boxes I'm currently working on.  These will be original designs and be made from unique and exotic woods, you know me; it's all about the wood!
     Virtually every piece of furniture I've ever built is finished with Danish Oil which is followed with a three part mixture that has pure gum turpentine as its' solvent.  This is hand sanded/rubbed onto it.  Generally, a minimum of 4-6 applications of this concoction leaves a finish that is beyond compare.  This finish was demonstrated by Art Espenet Carpenter at San Francisco State University when I was there in the mid 70's.  I've shared it with many woodworkers and the beauty of it is that it's very easy to repair and leaves a luster on the wood that can be felt and seen.
     So, where's the experiment you ask.  Well, I decided to try to substitute the pure gum turpentine with a synthetic, deodorized replacement called Turpenoid.  I did some research on the web and most of it was based on artists usage but I found some interesting tidbits of information.  The most interesting had to do with artists noticing that the residue in the bottom of their jar of Turpenoid used for cleaning brushes appeared stringy, something not seen with pure gum turpentine. The reason I wanted to try the Turpenoid was because of the odor of pure turpentine (which I happen to love!) but some may find objectionable.
     I noticed a few things about the Turpenoid, first of all it didn't dry as quickly and it felt "soft" to the touch.  No matter how well I rubbed it out, the next day there would be rougher areas and evidence of shiny  spots where the finish oozed out of the wood and dried on the surface.  Here's what I found:

Turpenoid vs. Turpentine

     I use a pie tin to hold the mixture.  The difference in color is because the tin on the right has been used for many, many years.  The Turpenoid has only been used for a couple of coats.  Pie tins are used since it's easy to saturate wet/dry sandpaper in them to rub into the finish.  See the difference?  Here's a closer look, this is the traditional finish with pure gum turpentine.  Note how it's dried:

Pure Gum Turpentine
    Compare that to the Turpenoid, see how it's dried -- very wrinkled appearance:


     I'm not a scientist but there is a definite difference and I'm supposing it has to do with how the solvent evaporates which effects the finish left behind.  The last test was similar to the Pepsi challenge.  I re-did one of the box lids with a single coat of the pure gum mix and had Diane do a blind folded "feel test".  In every instance she confirmed that the pure gum turpentine finish felt smoother than the Turpenoid one.  Scientific or not it proved that Turpenoid is an inferior solvent and it will no longer be used on my work!

   Hope I didn't lose too many of my followers!


  1. Sounded scientific to me, I'll stick to turpentine.. I've been experimenting on cherry using turpentine. Not as good feeling as the ones you have displayed but I'm getting there.
    Never though about using pie pan. I'll try that should make the sand paper work better.

  2. Bill, if you ever feel the need and want to "witness" the application of the finish let me know. I'm working on the box series and will be in various stages of finishing from now until September! After one coat of the turpentine on the 3 boxes I experimented with the Turpenoid they feel 100% better. Last application will be with denim.