Linseed Oil, Part II

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.

Making Sun-Thickened Linseed Oil

Linseed oil is made from the seeds of the flax plant. It is the strongest of the drying oils suitable for oil painting. Oil is extracted from the seeds under extremely high heat and pressure. The oil is then refined using strong alkali chemicals. The process is cheap, has high yields, and is done on a massive scale by a few large producers. Most commercial artist's paints are made from this oil.

The traditional process of making oil was far different. It was cold pressed and purified without harsh chemicals, usually just water. The process was slow and had lower yields, so it was long ago abandoned by industry.

I began making my own linseed oil the older way several years ago. It is not difficult, only time-consuming. I buy only organic cold-pressed flaxseed oil. an edible health supplement. The oil should be unrefined, and not have any additives. Before the oil can be used, it should be filtered of impurities.

I pour the oil into glass jars about an inch high. Distilled water is added to the oil and the contents are shaken so that they are thoroughly mixed.













The closed jars are placed to sit under the sun for several days. Our roof has a nice flat shelf to one side, so I put my oil up there.

The oil and water will eventually separate. Impurities such as mucilage become trapped in the boundary layer between the water and oil. I carefully remove the oil off of the top. I filtered this batch about three times over.













Properly cleansed, the oil is placed out in the sun again. I pour the oil into small bowls, place them in an old box, and cover it with glass. I've put little spacers between the glass and box so that air can circulate inside easily.

The sun will oxidize the oil, so that it becomes thicker and will dry faster. How long this goes on is up to individual preference. A month is typically required during the summer to get a thick oil. Every day I remove the glass and stir the oil, so that no dry film can form on the surface













The finished product is crystal clear, and has been bleached by the sun to a pale, straw-color. I'm still amazed at how simple and effective this process is. Used in a painting medium, the oil will dry in a few days, versus weeks for the typical store bought variety.