260: Re: De-fatting linseed oil

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Re: De-fatting linseed oil

In Reply to: Re: De-fatting linseed oil posted by JeffJ on 06/12/00 at 5:31 PM:

Jeff, I have spent the last month running experiments on washing oils, and the result, although inconclusive, are interesting.

I used a number of different oils in the experiments. The raw flax oil I used was absolutely fresh and, as you said, it separated out very nicely with a layer of stuff lying between it and the water. I decided to test what was in the water and in the layer of stuff under the oil. That would tell me what was removed.

Upon evaporating the water, the residue yielded thin flakes of what appeared to be gelatine. A drop of nitric acid confirmed that it was gelatin. There seemed to be some ash in the residue, but I do not have enough equipment to tell.

The stuff under the oil, which is often referred to as mucilage, was largely albuminous material and plant-derived mucilage. It dried clear and produced a tenacious adhesive. That's something one would find desirable in a vehicle. There was very little oil content in the "mucilage." That means that the washing process did not defat the oil. If anything, by removing the mucilage, the percentage of fats went up.

Running the same experiment with the SPecial Aged oil, just shaking it with water formed a perfect emulsion-like bond which remained unbroken for weeks. For a painter using emulsions, the was clear. The washed flax oil was more likely to separate than the refined oil.

Previous tests I have run with washed sun-thickened oils made by reputable makers, produced films that darkened considerably as compared with stand oil.

So what did I learn by applying scientific inquiry to the problem? 1) washing makes the oil fattier, 2) it removes a powerful adhesive which does not darken upon drying 3) washed oil makes an inferior emulsion which breaks down easily.

Whilst the bottle of oil and water sitting in the sun lended a certain medieval cachet to my window, the resulting product was no better and, I suspect maybe a bit worse, than the unwashed product.

Perhaps you will arrive at different conclusions when you examine the residue, but if there are not a bunch of saturated fats in the residue, it means that they are still in the oil.