Linseed oil is an oil which is pressed from dried flax seeds. There are a number of uses for linseed oil, ranging from furniture finishing to oil painting. Hardware stores and art supply stores often sell linseed oil, and typically there are several options available, all of which behave slightly differently when used.

It is important to distinguish between linseed oil and flaxseed oil. Although both oils come from the same seed, they are treated differently. Flaxseed oil is raw, cold-pressed linseed 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. If you want to eat flaxseed oil, make sure you purchase oil which is clearly marked as “food grade.”

One of the classic uses of linseed oil is in furniture finishing. Raw linseed oil not intended for human consumption can be rubbed into unfinished wood to create a rich, glowing finish. Typically, several coats of the oil 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 linseed oil is also added to things like paints, resins, varnishes, and inks, because it dries quickly, promoting rapid, even drying. Painters use linseed oil as a carrier oil for their paints, prizing the rich glow which linseed oil creates. Depending on the amount of linseed oil used, a painter can also vary the thickness of the paint, from very dense and clumpy to thin and ephemeral.

Treated linseed oil tends to be a dark amber color, and it has a distinctively sharp smell. The smell and color are a tipoff that the oil is not safe to use, if one has any doubts. 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, please be aware that it is highly flammable. As it evaporates, the oil can sometimes spontaneously combust, causing a fire. For this reason, cloths which have been used to apply linseed oil should be allowed to dry flat outside before being discarded or washed; these cloths should also not be run through a dryer, as they may catch fire.