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Oil, Extra Salt

Post #1840 • August 2, 2019, 9:52 AM

Because I'm obsessed, I tried yet another oil refinement recipe from Tad Spurgeon's book.

For each half gallon jar, 0.75 liters (3 cups) of oil, 1 liter (4 cups) of spring water, and 120g (3/4 cup) salt are used. The jars are shaken three times daily, and left on a windowsill. The water is changed one a week. Two week-length washes with salt are followed by one week-length wash with spring water only. The oil can then be heated gently and stored as above [in the book]. Alternatively, it can stand in the light until it clears (about two weeks), before it is processed further.

You can find further details about the necessary oil from my previous posts on this topic (one, two).

So it took five weeks, but I have a nice couple of cups of painting oil for my effort, and I learned some things along the way.

The recipe is adapted from the work of George Lock Eastlake, who is remembered chiefly for his Materials for a History of Oil Painting from 1847. Eastlake helped perpetrate some of the nonsense about the necessity of stuff like sandarac and copal in oil mediums for capturing the Lost Techniques of the Masters™ but the oil refinement method appears sound. Modern conservation suggests that a Rembrandt has three ingredients, oil, pigment, and chalk. If that's good enough for him, it's good enough for me.

The instructions say "stand in the light," and they mean it. Modern windows in New England have two panes of glass and a coating that reflects both ultraviolet and infrared wavelengths. This is great for your utility bill, but the energy you need to clear the oil is on the other side of the window. Putting it outside, at least when it comes to this house, is non-negotiable. I'm not a materials scientist, but my guess is that the IR, conveying heat, clears the microemulsion of water (which is harmless) out of the oil, while the UV fades the fugitive yellow color of the oil (which, lest a reminder be necessary, has nothing at all to do with the yellowing of the oil due to contamination or acidity).

Typically recipes recommend clearing the oil in a tray. In any case, exposed surface area relative to volume matters. I poured a batch of oil into two jars for sunning, a bit unevenly because it didn't need to be perfect. This was fortuitous because the jar with a quarter-cup less of oil than the other one cleared faster, by days. I grasped the point, and procured a glass-lidded ceramic casserole dish, poured both jars in, and set it in a sunny spot in the front yard. The glass lid let in light but not light rain. The white ceramic served as an able reflector. The lid let in air but was tight enough to keep out bugs, with the exception of a half-dozen especially determined or suicidal gnats. I filtered them out with a funnel and some cheesecloth.

That left only the Fridge Test, mentioned in the second post linked overhead, but repeated here:

To test Eastlake’s method, place a jar of oil cleansed by his method in a refrigerator overnight at 40 degrees Fahrenheit. If the oil is truly cleansed of mucilage, it will remain fully transparent no matter how long it remains in the refrigerator. DO NOT judge oil cleanliness when the oil is at room temperature. Even oils full of mucilage are fully transparent at room temperature. But, oil containing mucilage becomes cloudy in the coldness of the refrigerator.

The author of that passage prefaces it like so (edited to remove Time Cube-style formatting):

Washing the oil with Eastlake's 19th century method is ineffective. I have tested the method. Whether shaking the oil with water, or with water and salt, or with water, salt and sand, it is a waste of time, a loss of good oil, and ineffective.

I too have tested Eastlake's method. It comes out of the refrigerator as clear as apple juice. Go figure.

With that microemulsion of water, I was prepared for it to fail, and not worry about it. Again, the water is harmless. Plus, unlike in the previous methods, you can see the oil throw off layers of globular slime in diminishing quantities over the three weeks. If that's not mucilage, I have no idea what it might be instead.

Why go through all this trouble when methods that take hours instead of weeks are available? Because this method is purported to produce an especially fast-drying oil. Whether that pans out will be the subject of the next post on this topic.

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