Linseed oils are drying oils commonly having excellent drying characteristics suitable for manufacturing of paints and varnishes, wood preservative and as an agent to protect iron from rust. They are derived from the seeds of the flax plant by pressing crushed flax seeds. Drying of oil takes place not by evaporation but when linseed oil exposed to air, it gets oxidized, dried and form a protective layer. They are applied to a porous surface like wood, concrete, stone, plastered surface, etc. to fills the pores. They have superior drying quality.Because of this property; linseed oil makes a perfect vehicle for pigments. They allow to binding pigments in oil paints, good varnish in wood finishing, and plasticizer in putty.It is important to use refined linseed oil, as raw or boiled linseed oils can yellow the paint quickly because they are heat-treated.
There are various types of linseed oils used in the paints and varnishes are discussed briefly below:
01. Raw Linseed Oil:
It is a type of linseed oil which works as a vehicle in paints. It is transparent, yellowish in colour, sweet in taste and has very little smell. There is no additional additive or preservatives in the raw linseed oil.It dry very slowly, taking weeks to fully cure. Therefore, it is used where time is not a consideration.
02. Boiled Linseed Oil:
Boiled linseed oil is not boiled in the way most people think of as boiling.Slow drying limitation of row linseed oil is overcome by boiled linseed oil. Metallic solvents are added to the raw oil that encourages faster drying. The process is like boiling, which is why it is referred to as boiled linseed. Raw linseed oil can take weeks or even month to fully cure while boiled linseed oil is drying faster than raw linseed oil.
03. Double Boiled Linseed Oil:
Double boiled linseed oil has transparency and colour same as raw linseed oil. It is produced by heating raw linseed oil and then air is blown inside. It has quick and completely drying quality and a forms a film on the surface. It is often used as a pigment binder in oil paints, and in the paint industry to produce alkyd resins, drying oil finish or varnish in wood finishing.
04. Pale Boiled Linseed Oil:
It is a type of linseed oil which also works as a pigment binders in oil paints. Pale boiled linseed oil is better than raw oil and is same as ordinary boiled but it is not in dark colour.It is primarily used as a timber preserver as it offers increased water resistance.