Linseed oil is important enough that it qualifies to receive its own attention.
One of the first known drying oils, linseed oil is obtained from the seed of the flax plant – Linum usitatissium. Oil content varies from 32% – 43%, the quality and quantity depending on the variety of seed, where it is grown, and the climactic differences that vary year to year. The plant is mostly grown in Canada, Burma, India, Russia, Uruguay, Argentina, and the USA.
Its oil makes an excellent natural wood finish in both raw and refined states. Raw oil contains quantities of mucilaginous matter – waxes and grease. These will tend to remain active…the mucilaginous matter will never dry. Since raw linseed oil will remain wet for long periods of time it is never used by experienced wood workers other than for very specialized purposes.
Boiled linseed oil is not actually boiled, but is heat treated. It also contains added drying agents. Properly prepared boiled linseed oil gives more protection against moisture than raw oil. There is no other oil that imparts to wood such a beautiful finish as boiled linseed oil. It is known world-over as the finishing oil without peer. There is no contest that this item will give extremely fine finishes for indoor woods and should be seriously considered for fine wood work.
The case against using it is related to its relatively low moisture resistance. It does pass moisture freely. That makes it one of the reasons it is used both indoors (where the wood can swell and contract in response to internal humidity) and outdoors (where applications on new wood allow the wood to continue to freely expel moisture, instead of bubbling the finish).
Boiled linseed oil is superb as a weaving loom finish, intensifying the beauty and conditioning the wood all at the same time…easy to apply and dry in a couple of days. Apply light coats only with a paper towel. Yearly light applications will deepen the grain and further condition the wood. Always wear protective gloves. Dispose of towels outside only, preferably by burning or in an air-tight covered garbage container; saturated rags can spontaneously combust.