Flaxseed oil condensed by the sun 100 ml

Refined bleached linseed oil is placed in flat vessels in the open air (in the sun) with a lot of oxygen, which is why it thickens into honey.

This is the historical thickening of oil.

Initially, linseed oil was taken, refined bleached, (Color number no more than 10-15 mg of iodine), GOST 5791-81

It is extracted from flax seeds. The climate in the area where flax grows has a significant impact on the composition of the oil and the ratio of unsaturated fatty acids in it. The refractive index of olive oil is approximately 1.48.

Linseed oil is a quick-drying oil, since it easily polymerizes in the presence of atmospheric oxygen ("dries") with the formation of a strong transparent film. This ability is due to the high content of glycerides of unsaturated fatty acids - linoleic, linolenic and oleic. Sunlight accelerates the drying of oil, but after 10-14 days it becomes soft and even sticky again. The purer the oil, the faster it dries. Slower drying means a better quality coating. Oil does not dry in a dark place and in the absence of oxygen.

Oil can be refined and unrefined. Refined oil is obtained by pressing and extraction, unrefined oil - only by pressing. Only refined and bleached oil is used in painting.

Depending on the method of production, it is divided into cold-pressed or hot-pressed oil. The color of cold-pressed linseed oil ranges from lemon to dark lemon, hot-pressed - from golden yellow to brown.

Linseed oil contains pigments that determine its color. Thus, carotenoids present in the oil give a color from yellow (xanthophylls) to red (carotenes), especially p-carotene. These pigments are unstable to sunlight - they fade, so one of the ways to bleach (lighten) linseed oil is to keep it in the light.

To remove coloring compounds from oils during refining, special highly dispersed adsorbents are used.

Linseed oil remains liquid up to -16°C, then coagulation (formation of flakes) occurs, when heated to 40°C the oil becomes transparent again.

In the 18th century, Russian painters were recommended to use siccative linseed oil for making oil varnishes, which artists called drying oil or boiled oil.

Nowadays, especially pure bleached linseed oil is used to make painting varnish. Excess substances are removed by heating to 85°C and adding bleaching earth (clay with high adsorption properties). This improves oxygen absorption, which speeds up the drying process. It is used to make white varnish and artistic paints.

Thickened linseed oil for painting is a product of special processing of linseed oil, previously aged and freed from protein mucus and other harmful impurities by refining and double bleaching, used in oil painting as a paint thinner. It differs in its properties from ordinary bleached linseed oil in that its film has a lower ability to wither and give "settling" (wrinkling), is less prone to yellowing, and is more moisture-resistant. At the same time, this oil is less absorbed into the base material.

Due to the increased refractive index, thickened oil gives paints improved optical properties and prevents the lightening of some pigments.

Oxidized linseed oil for painting is refined, bleached and aged oil, then subjected to thickening by oxidation with atmospheric oxygen in sunlight. This oil is a classic product described in ancient treatises. Nowadays, oil oxidation is carried out by blowing air through a layer of oil heated to 110 - 150°C. It differs from other types of linseed oil in that it dries faster and has the least yellowing in films. Due to the appearance of hydroxyl groups as a result of oxidation, it has a good emulsifying capacity.

Refined or oxidized drying oils, when modified with sulfur (in an amount of about 5%), acquire a darkish shade. They are capable of forming films that quickly harden after minor oxidation. Such oils gelatinize during long-term storage.