We have been experimenting with hemp oil, primarily mechanically-refined, cold-pressed oil from hemp seeds. (For those of you whose heart raced when reading the foregoing sentence with the idea of painting and getting off on hemp oil paint in one brushstroke, you’ll be disappointed; hemp seeds contain insignificant amounts of THC.*) We were interested in the visual appearance, handling qualities and performance of pigments ground in hemp oil, so we have been experimenting with it.
However, considering that the cost of hemp oil is at present nearly double that of linseed oil, we do not see any major advantage to using hemp oil in artists’ paint formulations. In our experience it does not dry faster nor harder than linseed oil. It yellows less than most varieties of linseed oil, but not significantly less than other drying oils, such as walnut and safflower oil. Its best qualities, however, may be in its combination with other drying oils, something we are currently exploring. We are also examining it as a varnish or medium oil where it is "cooked" with other oils and resins.
Although I have read that hemp oil was used in quality paints, I simply do not find evidence of its widespread use in modern paint making (that is, since the 19th century). The major oils used in paint making have been linseed oil, tung oil and, since the latter half of the 20th century, safflower and soya bean oil. It may have been used by the old masters, as they often used materials that were readily available, but it was not as widespread as linseed oil.
A review of literature for hemp oil in painting reveals the following:
It is mentioned in oleoresinous varnish recipes by Charles Lock Eastlake in his book, Materials for a History of Oil Painting, Volume I, page 279. It is also described in varnish recipes of the 19th century, and said it is used in paint of the last two centuries, but it is seldom found in manufacturers’ textbooks and papers of that period.
Johannes Rudolf Wagner. Manual of Chemical Technology. J & A Churchill, 1904. Page 906.Hemp-oil, obtained from the hemp-seed (Cannabis sativa), containing about 25 per cent, of oil, chiefly used for making black, green, or soft soap. When fresh pressed, hemp-oil possesses a bright green colour, which in time becomes a brown-yellow.
Max Doerner. The Materials of the Artist and Their Use in Painting. Revised Edition. Houghton Mifflin Harcourt, 1984. Page 113.Hemp oil, the first pressing of which is colorless and later pressings greenish. It dries more slowly than poppy seed oil (in about 8 days) , but unfortunately wrinkles most of all the fatty oils and is, because of its greasy nature and its gloss, least useful for purposes of modern painting. Coats with Cremnitz white tested very well, without yellowing. Hemp oil is used as additions to other oils , since it has some good qualities.
We are not certain about the word "greasy" chosen by the translator for the original German text. I do not have access to the German text, so I cannot comment on this expression. In English, the word is suggestive of slickness or slipperiness. It is appropriate designation for fatty oils that contrasts to the opposite sensation of tackiness and drag experienced with bodied oils. But how this sensation differs from that of other drying oils, such as linseed oil, I am not sure. It does feel more slippery than other common drying oils, but how this affects painting, except in some way of its handling in paint, I cannot say for certain. I also have not observed the "wrinkling" of paint made with hemp oil. However, I do agree with Doerner's observation of its effectiveness when lead white is ground in it.
Cornelia Syre, Andreas Burmester, Editors. Tintoretto: The Gonzaga Cycle. Hatje Cantz, 2000. Page 224.Since hemp oil, among all fatty oils, is (allegedly) the one that shrivels most...
This quote appears to be a reference to Max Doerner.
Hemp oil is composed of the following fatty acids:
C 16:0 Palmitic 4-6%
C 18:0 Stearic 2-3%
C 18:1 Oleic 8-12%
C 18:2 Linoleic 44-57%
C 18:3 Linolenic 15-20%
Higher unsaturated fatty acids, such as linoleic and linolenic, promote rapid drying and tougher films.
It has these typical values:
Iodine Value 155-170
Low iodine values typically denote slow drying oil, wile high values mean faster drying. This range is comparable to walnut oil.
Free Fatty Acid (FFA) 3-5%
Free fatty acids are important for pigment wetting and when grinding with reactive pigments.
Peroxide Value 3-5%
The peroxide value is used as a measurement of the extent to which rancidity reactions have occurred during storage. The double bonds found in oils play a role in autoxidation. Oils with a high degree of unsaturation are most susceptible to autoxidation. The best test for autoxidation (oxidative rancidity) is determination of the peroxide value. Peroxides are intermediates in the autoxidation reaction. This is not a significant value used in paint making.
Unrefined hemp seed oil extracted by cold-pressed methods varies in color from yellow to dark green. When refined it is nearly colorless.
Major sources of hemp seed oil are China and Canada.
* Hemp seed oil is pressed from varieties of Cannabis sativa that do not contain significant amounts of THC, the psychoactive element present in the cannabis plant. There is little or no THC within the hemp seed, although trace amounts may be found in hemp seed oil when plant matter adheres to the seed surface during pressing. The manufacturing process includes cleaning the seed before pressing the oil.