HEMP OIL AND PAINTING
Dutch masters used hemp oil in their paintings, but since then linseed oil has become much more common. When I heard this I tried using hemp oil in my own artwork, and brushed on a patch of each on to an oil primed canvas. (Which, as the name implies, was made of hemp - Cannabis sativa - but is now usually made from flax). After some months the linseed oil yellowed, but the hemp oil was clear.
Observing this, I turned to The Artist's Handbook by Ralph Meyer, and this is what he had to say on the drying of oils:
"The drying properties of most oils are due to the presence of glycerides of linoleic and linolenic acids, which have the properties of combining spontaneously with atmospheric oxygen to start a chain of reactions which end in the conversion of the oil to the tough, durable film known as linoxyn. The action of the moisture on certain of the glycerides of linoleic acid, particuarly in the absence of daylight, is also one of the chief causes of the yellowing of oil films. Linseed oil has a larger percentage of linolenic acid and its glycerides than any other drying oil except perilla oil...compared with linseed oil, poppy oil containes a smaller total amount of these glylcerides, and little or no linolenic acid, and this minimizes one of the causes of yellowing of its films".
p. 355, The Artist's Handbook by Ralph Meyer, 1945 edition.
[related information on this blog can be found by clicking on labels or a word search. Percentages of linoleic and linolenic acids can be found for a number of different hemp varieties on a previous post]