Saturday, 29 January 2011

Hermitcraft: Trinity Tar

(I mentioned this stuff last time, and since it's a handy thing to have around, here are the particulars for anyone who'd like them.)

Trinity tar has been around forever. It's the West's original varnish, our equivalent of Asia's lacquer and t'ung oil. And unlike a lot of pre-industrial standbys, it can still be whipped up from ingredients found in any hardware store. You may even have them sitting around the house right now.

Everybody ready? Sharpen your pencils and listen carefully, cos here it comes:

f 1 part boiled linseed oil
1 part gum turpentine
1 part white vinegar

Method:

1. Pour ingredients into a tightly-lidded container.
2. Shake

Shhhhh. Don't tell anybody.

Yeah, that's all there is. The chemistry works like this: linseed oil cures with exposure to oxygen, into a hardish, satiny, impermeable surface. Boiled linseed oil (which in our day is really chemically treated) dries much faster than raw. Turpentine thins it up to penetrate more deeply. Vinegar contradicts the oil's natural tendency to mildew.

The proportions can be altered according to taste and application. When used to finish furniture (an excellent idea, by the way), the vinegar is sometimes eliminated, since the expected environment is dry. But at least half the reason to use this stuff is its smell, very homey and aromatic and unpetrochemical, so I always add vinegar for the bouquet. Hey, you can never have too much (medically benign) antifungal.

And the fact is that in its traditional form, trinity tar is about as inoffensive as it gets. If made with raw oil instead of boiled, you could even use it as vinaigrette, which it closely resembles in the jar. In fact, I'm told veterinarians once used the same philtre to treat constipation and colic.

Users have developed their own tweaks on the formula to need. Sometimes a measure of commercial varnish is added to get a faster, harder finish. (Generally half a part or less, in my experience.) For outdoor use I replace the gum turpentine with paint thinner to give the mix even more antifungal kick, and may add a touch of roofing tar as well, to darken it up. (See photos of some of these projects here.) This is, after all, the Urpaint; pretty much all paint started as trinity tar with added colorant.

Application is simple. After sanding the wood, lay on a thick coat of trinity tar. I usually apply the first coat with a brush, to get as much on as possible. Then leave the piece alone for an hour or so, or until most of the oil has been absorbed, and repeat. (This can happen once, or go on for a day, depending on what kind of wood you're working with.) When the oil no longer disappears quickly, rub that final application well into the wood with a soft cloth, until evenly distributed and no slicks remain. Leave the piece to dry overnight. (Faster if set near the woodstove.) You can repeat this step ad infinitum, deeping the finish each time, but never leave wet oil on the surface of the wood; it will coagulate into a dirty, gummy mess.

As this is an emulsion (an uneasy alliance of oil and water; remember the salad dressing?), it needs shaking up a bit during work to stop it separating.

In a matter of weeks the finish will oxidise to a pleasing honey colour, and continue to smell great when it warms, as when the sun streams in or you handle it. The finish can be updated occasionally by a good wiping down with straight turpentine, then reapplying as before. To remove it entirely, either sand the piece lightly or scrub well with naphtha.

In its purest form, this concoction will neither offend chemical sensitivities nor provoke same in habitual users, and will impart to any room a memorable "Grandpa's house" glow and smell, at least if you come from country people. Let me know if you innovate on the recipe; it's all about the experience.


2 comments:

  1. Thanks! I'll try it.
    I've enjoyed your blogs.
    Rico

    ReplyDelete
  2. Thanks, Rico. It's a lot of fun to write.

    Robin

    ReplyDelete

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