Linseed Oil

The oil reaches buyers in several distinct states, and they are different articles rather than qualities of one. Cold-pressed oil, minimally processed and kept cool, is the food grade sold as flaxseed oil. Raw linseed oil is the untreated industrial article. Boiled linseed oil, despite its name, is generally oil treated with driers to speed curing rather than simply heated. Stand oil is oil that has been heat-polymerised to a thicker, more controlled-flowing product for fine finishes.

Raw linseed oil

Untreated pressed and filtered oil, which cures slowly by air oxidation alone.

Boiled linseed oil

Oil containing added driers to accelerate curing; the name is historical and does not reliably describe the treatment.

Stand oil

Oil heat-bodied under conditions that polymerise it before use, giving a thicker oil with different flow and film properties.

Linseed oil is a classic binder: it is the film-forming component in traditional oil paints, varnishes, and wood finishes, and it is a constituent of putty and of linoleum, whose name records its origin. Synthetic binders displaced it from much of the coatings market over the twentieth century, but it retains a durable position in wood finishing, artists’ materials, restoration work, and applications where a plant-derived binder is specified.

• Coatings — oil paints, varnishes, and wood finishes
• Building materials — putty and linoleum flooring
• Artists’ materials — oil paint media and grounds
• Food — cold-pressed flaxseed oil as a nutritional oil
• Industrial — oleochemical intermediates and printing inks

Industrial buyers describe the oil by its drying behaviour, colour, free fatty acid content, and moisture and impurities. Food buyers describe it by freshness and flavour and treat the same reactivity as a shelf-life problem, which is why cold-pressed flaxseed oil is packed opaque, kept cold, and dated short.

The oil is stored in closed containers with minimal headspace and away from heat and light. This is not general good practice repeated for form’s sake: an oil that cures on contact with air will begin doing so in a partly empty drum, forming skin and rendering the contents unusable.