Asphaltum – You gotta get some

Over the last few years, I’ve noticed that there has been renewed interest in (and something of a mystery about) the use of asphaltum in wood finishing.  It comes as no surprise that once one of the most widely used products for protecting and finishing wood, is now almost unknown to the majority of modern wood workers.  Or, is it?

The product has many names; asphaltum, asphalt, bitumen, pitch, tar.  It may be liquid (think LaBrea tar pits) or solid (Gilsonite, a high quality mineral asphalt or simple coal).  Over the millenia it’s been used as an adhesive, a waterproofing material, a decorative finish, a paving binder and a medicinal.  Tar can be extracted from pine, birch and numerous other trees.  At one point, the harvesting of pine pitch was one of the largest industries in North Carolina.  Pitch, tar, turpentine and rosin (colophony) were all materials made in the distillation process.

During the period of sailing ships, tar had many uses.  It was used as a protectant  for rope, sail cloth and straw hats, to name a few.  Nelson Checker, the famous color scheme of the British Navy, was influenced by the fact that hulls were painted with asphaltic paints.  Mast heads and spar tips were varnished with a black asphaltic long oil (spar) varnish.

“Black Japanning” was a commonly used method of protecting metals right up to the beginning of WWII.  Black Japanning is simply a formulation of three main ingredients; asphalt, boiled linseed oil and turpentine.  Ford Motor Company used several formulations of Black Japanning.  The first a “long oil” varnish (less asphalt, more oil, turpentine) was used as a primer and on parts that required a more “elastic” finish.  The second, a “short oil” varnish, as a final finish on parts experiencing less flexure.  Occasionally, lamp black or very finely ground coal dust might be used as an additional pigment.  Distillation quality of the turpentine (the volatile oil) or the addition of a metallic drier (probably) allowed some control of drying time.  Of course, anyone with an interest in metallic hand planes knows that all of the major tool producers used Black Japanning to coat the “non contact” iron surfaces of their planes.

So, what does this have to do with today’s woodworker?  Well, first things first.  Next time you’re at your favorite finishing store, notice how many brown wood stains list asphaltum as an ingredient.  The picture above is a good indicator of how many shades of brown can be created by a simple dilution of the product.  In varying formulas (tar, BLO, turpentine), asphaltum can be used as a rubbing stain, a glaze, an oil varnish (tar, BLO, turpentine) or spirit varnish (no BLO, turpentine or naptha).  I, for one, am always looking for ways to reduce the number of finishing products in the shop.  I want products that allow me to create the finishes I want and have good shelf life.  Plus the fewer cans and bottles I have laying around, the fewer I have to get rid of (a task that becomes more challenging as municipal waste rules evolve).

There are numerous sources for asphaltum products.  My major concerns are quality and a fair price.  Art stores offer Asphaltum Etching Varnish, Gilder’s Asphaltum, Asphaltum Artist Color, and Asphaltum Glazes.  That said, for what I’d pay for two pints of Gilder’s Asphaltum I can buy a five gallon can of Henry 101 Non-fibered Foundation Coating (Asphalt and Mineral Spirits).  (A caveat:  stay away from construction products that are rubberized or fibered.)  You might, rightfully, ask “what am I going to do with five gallons of asphalt?”  One suggestion I would offer is to give all of your woodworking friends “a bottle for Christmas.”

 

 

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3 Comments on “Asphaltum – You gotta get some”

  1. Paul Bouchard Says:

    Our hundred year old house and the neighbouring homes all had dark stained Douglas fir trim. The finish looked like a thick, single coat of glaze. It darkened the wood dramatically without the blotchy effect that I kept running into when I’d try to match new trim to it. I’m wondering if the glaze was some version of what you’re describing. I’ve looked online for info and it’s always seemed strange to me that a technique so widely used could be forgotten.

    • D.B. Laney Says:

      I wouldn’t be at all surprised. Commercial “tar paint” was available in the U.S. right into the mid 20th century. A British manufacturer still produces a product listed as traditional tar paint. I just found a video on Youtube about the pitch and tar business in Colonial North Carolina. Surprisingly, one additive that was commonly used was dung (which was also used in exterior plasters). Our ancestors didn’t waste much.

  2. Torstein Says:

    In Norway we use pine tar for boats, houses and different woodwork. It smells good, leaves a nice finish and protects very well. I believe this is toxic to a certain degree, we usually air out well, or work outside, if heating it up, or applying large amounts.

    Bitumen, beechum, or pitch, is something else completely. It’s used on wooden telephone poles, was used on railway beams, and is used on old historic wooden ships. It is toxic. We use protective dresses, glasses and gasmasks while applying it. (it’s hard as ‘glass’ at room temperature, so it has to be heated before use)
    I would never use this on anything that goes near humans!


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