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Linseed oil is an oil that is pressed from dried flax seeds. It has a number of uses, ranging from furniture finishing to oil painting. Hardware stores and art supply stores often sell it, and typically there are several options available, all of which behave slightly differently when used.
It is important to distinguish between linseed and flaxseed oil. Although both oils come from the same seed, they are treated differently. Flaxseed oil is raw, cold-pressed oil, and it is often sold as a dietary supplement. Linseed oil is heated and subjected to chemical treatment, and it is not safe to consume. People who use flaxseed oil as a dietary supplement want to take advantage of the rich nutritional value of the oil in raw, cold-pressed form. People who are interested in consuming this oil should make sure they buy a product that is clearly marked as “food grade.”
One of the classic uses of linseed oil is in furniture finishing. Raw oil not intended for human consumption can be rubbed into unfinished wood to create a rich, glowing finish. Typically, several coats are required, and it takes a long time for the finish to dry between coats, so this finishing process requires some patience. So-called “boiled” linseed oil, which has been treated, dries much more quickly, allowing people to make several coats in a short period of time.
Treated oil is also added to things like paints, resins, varnishes, and inks, because it dries quickly, promoting rapid, even drying. Painters use it as a carrier oil for their paints, prizing the rich glow that it creates. Depending on the amount of oil used, a painter can also vary the thickness of the paint, from very dense and clumpy to thin and ephemeral.
Linseed oil that has been treated tends to be a dark amber color, and it has a distinctively sharp smell. The smell and color are a tip off that the oil is not safe to consume. Flaxseed oil, on the other hand, is a pale golden color, and it is virtually odorless and tasteless.
When using linseed oil for home improvement projects, people should be aware that it is highly flammable. As it evaporates, the oil can sometimes spontaneously combust, causing a fire. For this reason, cloths that have been used to apply it should be allowed to dry flat outside before being discarded or washed; they should also not be run through a dryer, as they may catch fire.