Replies

1. 
   SteveSchoene | May 13, 2009 06:03pm | #1

   Pure tung oil is the raw oil from the tung or china nut tree.  It takes a long time to cure, so that when you try to use it as a finish you should wait several days between each coat.  Oils, including tung oil, are quite soft when they do cure.  Consequently you can not leave them to build a film on the surface--they would be almost gummy.  Tung oil would require 5-6 coats, lightly sanded between each coat to achieve an even dull satin sheen on most woods.  It would have minimal protective properties--a shade more resistant to water spotting than pure linseed oil.  It's slightly lighter in color than linseed oil, but without side by side comparisons I doubt anyone could tell the difference. 

   Modified tung oil comes in two categories.  First there is polymerized tung oil.  This is tung oil that has been partially "cooked" to begin the curing process.  It dries quickly, and a bit harder so you could allow a thin film to build.  It is challenging to apply on large surfaces. 

   But the most prevalent form is something called "Tung Oil Finish"  The operative word is finish the words "tung oil" are just adjectives telling you that they think you will think it looks like tung oil.  Formby's Tung Oil Finish is one brand.  It is not tung oil, in fact not oil of any kind.  It is a wiping varnish manufactured from soya oil and alkyd resin.  Oil was an ingredient in making the varnish, but once chemically combined with the resin is no longer oil.  Varnish dries harder and can be and usually is allowed to form a film on the surface.  Some other products are also labeled Tung Oil Finish that aren't varnish, but are mixes of oil and varnish.  Minwax makes a Tung Oil Finish that is of this variety.  Like all oil/varnish mixes (others are called things like Danish Oil) these two would dry too soft to be allowed to dry into a film on the surface.  Just like pure oils they are applied, let penetrate for a bit, and then thoroughly wiped off of the surface.  The will be more protective than pure oils, tung or linseed, but will look virtually the same. 

   So why are companies "deceptive" about promoting tung oil finish--tung oil developed a mystique, but the actual product is so hard to use and to get good results that most manufacturers don't really like putting out products that are on the edge of being defective. 

   The message--if you want an in-the-wood "oil" finish, use a mix of oil and varnish.  If you want more protection, use a film finish such as varnish. 

   So when do you use tung oil--almost never.  A single coat of boiled linseed oil will "pop" grain almost identically to tung oil, but be cheaper and dry faster.  Tung oil contributes good properties as an ingredient in the manufacture of varnish, but very little good when used directly by consumers. 

    

1. 
   EdGladstone | May 13, 2009 06:35pm | #2

   Thank you.  I appreciate the amount of detail and guidance on how to procede.

1. 
   saschafer | May 13, 2009 07:06pm | #3

   A little different take: About three years ago, I made a cutting board from red (soft) maple, and finished it with three coats of raw tung oil, applied about a week apart. The tung oil took forever to dry completely (it was probably two months before the smell was no longer noticeable). But I find that it resists water surprisingly well. It gets used maybe once a month on average, and is washed thoroughly with dishwashing detergent and hot water after every use. I haven't done anything to rejuvenate the finish at all, yet I can still leave water beaded up on it for hours without it soaking in.

   -Steve

    

1. 
   dkellernc | May 13, 2009 10:31pm | #4

   A slightly different take than the two above - I use BLO and pure tung oil on a regular basis for small objects that don't have to resist water/acid/alkali/solvents like a table top would.  The tung oil I use is indeed tung oil with no varnish added (typically, Behlens), but it isn't raw tung oil - it has metallic dryers added (as does "boiled" linseed oil).

   Typically, I find that the tung oil cures considerably faster than does the linseed oil, and results in a darker appearance to domestic species and mahogany (which I consider desirable in some applications).

   Polymerized tung oil, but the way, is used quite a bit as a gunstock finish.  Properly applied as 10-20 coats and cured (sometimes with the assistance of heating), it provides a quite hard, very durable finish.  But I dang sure wouldn't want to use it on a table top - way too much work.