Using the best oil possible is key not only to making paint with the best handling qualities, but also ensuring that a painting ages gracefully. While linseed oil naturally yellows a certain extent over time, an inferior oil will be far worse. In the picture above, the unsightly brown goo is nothing more than linseed oil that has separated from the paint and oozed out of the tube. What is surprising is how awfully brown this modern oil has become.
Over the past month, I have set aside some time to improve my homemade linseed oil. My goal was to speed up and improve the process of refining the raw oil.
The key to speeding up the process was finding a more effective method of removing the heavy fatty acids, or mucilage contained in the raw, unfiltered oil. These impurities are the key cause of unsightly yellowing seen in oil. I wanted to filter the oil mechanically, without the resorting to the strong chemicals used in the production of commercial oil.
In the past I have cleaned my oil with water and sunlight, this method was time-consuming and had to be done in warm weather. Other historical practices suggested washing the oil with a mixture of sand, salt and water. This was also time consuming and repetitious.
A variation of this method substitutes sand for a mixture of diatomaceous earth and cristobalite. These are simple forms of silica, used as a harmless filter medium. The calcined form is easy to find unadulterated, as used in pool filters. The process is new to me, other artists such as Tad Spurgeon have been making their oil using this method for some time.
I mixed one part D.E. with two parts raw flax oil, added a pinch of salt and three parts water. The jars containing the oil were put in a warm spot and shaken periodically over the course of a few days, to disburse the mixture.
The early results were dramatic. Most of the filter mix has settled to the bottom of the jar. The heavy fatty acids have become trapped in the boundary layer between water and oil.
The oil was siphoned off the top, filtered and the process was repeated again several times with fresh ingredients. Salt was used only in the first cleaning.
Not being completely satisfied the oil was good enough, I put the oil on the roof and washed it a few times over several days with water.
Looking down through the jar shows an almost clear oil, very little mucilage remains.
The appearance of the oil has definitely changed.
The oil was put into a newly-built glass box on the roof, to briefly sun-bleach. It will then be set aside for awhile to age, before being put to use.
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