Linseed oil is extracted from flax seeds, and the quality of the resulting product largely depends on the place of cultivation of seeds, their maturity and purity. Thus, the oil obtained from weed seeds contains an admixture of rapeseed, rapeseed and other oils.
The oil squeezed out without heating the seeds is light and has a golden yellow color; when hot pressed, a much more colored oil is obtained, often of a brown color with a characteristic odor and a rather pungent taste, devoid of transparency due to foreign impurities contained in it. Fresh oil obtained by cold pressing is devoid of any odor that appears in it later, probably due to partial decomposition of the oil.
Linseed oil, like other fats, consists of carbon, hydrogen and oxygen. Its solid fatty acids are mainly palmitic and stearic, the total content of which in one of the Dutch oil samples, according to the analysis performed by Eibner and Schmidinger, was equal to 8.3%. The liquid acids of linseed oil consisted of oleic acid, which is in it in an amount of 4.5%, linoleic. acids in the amount of 58.8%, linolenic - 20.1% and isolinolenic - 2.7%.
The composition of linseed oil, like other vegetable oils, is by no means a constant value, as was believed relatively recently, but is completely dependent on the climate in which the plant grows and from whose seeds the oil is obtained.
This highly important discovery belongs to Prof. S. Ivanov. Later analyses of linseed oil perfectly confirm the truth of the conclusion of Prof. Ivanov. So, it is found that in the northern latitudes in the composition of linseed oil, instead of two types of linolenic acids, there is only one.
Drying of linseed oil, as well as other fatty oils, is due to the presence of three named acids in them: linoleic, linolenic and isolinolenic. The total amount of these acids in linseed oil, as can be seen from the figures given, reaches 81.6%. This predominance of these acids in the composition of linseed oil explains its ability to dry quickly. Linseed oil, applied in a thin layer on a glass plate, hardens in its entire thickness after a while. If the oil is taken in a thick layer, then its solidification occurs first only on the surface, which is covered with a skin that quickly takes on a wrinkled and wavy appearance, since the hardened part of the oil increases in volume under the action of oxygen. This phenomenon is especially characteristic of linseed oil. Freshly squeezed cold linseed oil dries in winter in 11 days, in summer in 3-6 days.
Raw, freshly squeezed linseed oil, like other oils, usually contains more or less mucus, water and other foreign impurities that entered the oil during squeezing. Mucous impurities consisting of protein substances may be in a completely transparent oil, the turbidity of the oil does not indicate the presence of mucus in it. Water in freshly squeezed oil can be contained in an amount of up to 0.3%, and the transparency of the oil is also not a sign of its absence in the oil. The presence of mucus and water in the oil reduces its quality, and therefore they must be removed from the oil. The oil purified from mucus and water is called lacquer oil.
Linseed oil dissolves easily in essential oils and very little in alcohol: 1 part of it dissolves in 5 parts of boiling and 40 parts of cold alcohol. Oil, which has been stored for a long time in an open vessel and has thickened, acquires a greater ability to dissolve in alcohol. This solution is used to give elasticity to alcohol lacquers. At a temperature of - 6 g. The whole oil becomes cloudy, at - 16 gr. C is very thick, and at - 20 gr. C freezes completely; with stronger cooling, it becomes completely solid.
The dye principle that gives color to linseed oil consists of four pigments that are chemically similar to each other: yellow xanthophyll, yellow and blue chlorophyll and red erythrophyll. Not all of them, however, are present in the oil at the same time. The oil has a brown color if it contains erythrophil and a mixture of yellow and blue chlorophyll, and light yellow if xanthophyll predominates in it. All these coloring principles are non-light-permanent and therefore more or less quickly destroyed by light, especially in the presence of oxygen in the air. Heating the oil also strongly discolors them. The most durable color has Baltic oil, which discolors with difficulty. Weed flaxseed gives a cloudy oil with a greenish tinge and a weak ability to dry.
The gains and losses in weight, usually observed in fatty oils during the drying process, are not as great in linseed oil, as, for example, in walnut and poppy. This has a very favorable effect on the strength of the dried layer of linseed oil, which is therefore less capable of cracking than layers of poppy and nut oils.
Linseed oil as a binder of paints surpasses all other oils in its qualities.
The oil paintings of the past are executed mainly on linseed oil, and this largely explains its excellent preservation. A serious disadvantage of linseed oil is its ability to turn yellow and darken. Dried in the dark, linen drying oil acquires a red-brown color. Bleached linseed oil also turns yellow, red and darkens when stored in the dark for a long time. The same thing happens with paintings made with linseed oil and stored in the first period of its drying in the dark and damp. Under the influence of direct sunlight, the painting returns to its former tone, which can be lost again in the shade. The old masters, who painted on linseed oil, dried all fresh paintings, in order to avoid yellowing and darkening it, in sunlight.
A later study of the issue of yellowing observed in linseed oil under the above conditions convinced that the cause of yellowing is one of the components of the oil, namely linolenic acid, if it is in the oil in a free state. The fact is that all oils containing this acid in their composition usually turn yellow. Perilla oil turns yellow especially strongly, as it contains the largest percentage of it. Eibner also points out a means to eliminate this drawback, which will be discussed below.
Poppy seed oil
Poppy oil is extracted by pressing poppy seeds. The varieties and color of the seeds are reflected in the varieties of oil obtained from them. White poppy seeds are considered more valuable, as they give more oil, moreover, of the best grade. When cold pressed, an almost colorless oil is obtained, pleasant in taste and odorless. The oil obtained from other seed varieties has a dark color and represents the lowest grade of poppy oil.
Poppy oil in its chemical composition, like other fatty oils, based on the theory of Prof. Ivanova, in different samples may be different. In general, it differs significantly from linen. Solid fatty acids account for about 5% of the total amount of fatty acids in it, with lauric acid between them. There is much more oleic acid here than in linseed oil, namely 30%, linoleic acid about 60%, other linseed-butyric acids usually account for 5%, but Eibner believes that poppy oil does not contain the latter at all, and its comparative drying speed is due to the structure of oil glycerides. Due to the presence of a large amount of oleic acid in poppy oil, its drying ability is significantly lower than linseed oil. So, if it takes 3-4 days for a layer of linseed oil to dry out, then it takes 6-8 days for a layer of poppy oil, and even during this period of time, poppy oil does not have time to dry out to the extent that linseed oil. In addition, linoxin of poppy oil is significantly inferior in quality to linoxin of linseed oil.
In the process of drying, poppy oil initially increases greatly in weight, but then loses significantly in it, forming a large percentage of volatilizing substances. This feature of poppy oil, characteristic of oils of this type, has a bad effect on the strength of the paint layer built on it, since this layer is easily covered with cracks. The best technique of painting on poppy oil is therefore a single-layer painting, to which this oil is most suitable, since it allows you to paint raw for 5-8 days, and moreover gives the oil paints grated on it a pleasant pasty, and not fluidity, like linseed oil. Multilayer painting on poppy oil, based on what has been said, requires great care and careful drying of each layer, zinc whitewash is especially dangerous in this case. There are, however, opponents of poppy oil in the painting of Alla prima (Alla prima - immediately, with one reception). Oil paint on poppy oil from ten years ago, when tested with cotton wool soaked in turpentine, remained on cotton wool. The same experience with linseed oil did not give traces of paint on cotton wool. When the poppy oil dries, the surface of its film does not shrink, which is so characteristic of linseed oil, but this film, which is sufficiently dried, often softens in the shade and gives off.
This oil, when stored for a long time with air access, becomes rancid more easily than linseed oil, and acquires a special smell and taste. Poppy oil freezes in the cold at a higher temperature (-15 gr. C), rather than linseed oil.
Nut butter is obtained from nuts of various tree species, but mainly from hazelnuts, the grains of which contain up to 65% of the oil related to non-drying oils. Pine nuts of our Siberian forests are abundant in oil, the applicability of which for scenic purposes has not yet been sufficiently investigated. Only walnut (Volosh) nut oil is used in painting, but its use is limited due to the high cost and comparative rarity of this type of oil. Walnuts are aged for several months, and only then they start pressing them, since good grades of oil are not obtained from fresh nuts. Cold pressing gives a slightly colored oil that has no smell; hot pressing, to which nut cakes are subjected, gives a very low grade of oil.
Walnut oil, valued for its whiteness and other qualities, was used in painting already in the old days. Leonardo da Vinci in his famous treatise on painting describes the extraction of it.
Fresh walnuts were first peeled from the shell and immersed in clean water, where the skin covering them got wet and was easily removed from the nuts. Then they were transferred to fresh water, which changed several times after turbidity. After a short period of time, the nuts were so softened that, when stirred, they turned into milk, which was then poured into flat vessels and exposed to the sun. Under the influence of the warmth of the sun's rays, pure light oil settled on the surface of the liquid and collected with the help of cotton wool, which absorbed the oil.
Nut butter at a temperature of -15 gr. C thickens, but hardens only at -30 g. C. Of solid fatty acids, it contains myristic and lauric; as for liquid fatty acids, their percentage in oil, according to Hazura, is as follows: oleic - 7%, linoleic - 80% and linolenic - 13%.
The drying capacity of walnut oil is lower than linseed oil, but exceeds that of poppy oil. Cold-pressed oil is easily bleached and becomes completely colorless. Nut butter, like poppy oil, does not turn yellow and does not darken to the same extent as linseed, but it easily rancid and softens after drying like poppy oil; as for the formation of cracks, in this respect it is inferior to linseed, but certainly more reliable than poppy oil, since its layer dries out simultaneously in the entire thickness. There is almost no wrinkling of the oil layer with nut butter, and in this respect it is superior to linseed oil. It is not without reason that they believe that poppy oil should be replaced in painting with walnut oil.
Sunflower oil is extracted from sunflower seeds. Its production is very extensive in the former USSR, in Western Europe they are not familiar with it, and therefore it has not had much use in painting yet. Sunflower oil as a material suitable for painting was pointed out for the first time by Prof. F. Petrushevsky.
Raw sunflower oil, squeezed cold, has a light yellow color, which more or less easily disappears in the light and when heated. Its chemical composition is still poorly understood. [b]Farion refers sunflower oil to semi-drying oils. that is, the oil dries partially. When removing the hardened film, we find that the oil has not dried out. This oil is of great interest to Russian painters, since it is extracted mainly in the former USSR, moreover in large quantities, and is cheap. Recently, however, they have also become interested in him in the West, where tests of his suitability in painting are also being carried out.
Sunflower oil contains 46% linoleic acids, 39% oleic acid and 9% solid fatty acids. These data on the composition of the oil, apparently, are close to the truth, as they are confirmed by the slow drying of sunflower oil. But while there is no firmly established data, it is necessary, of course, to further study the composition of sunflower oil. Mixing paints with sunflower oil gave certainly satisfactory results, but the drying time negated all efforts.
a layer of sunflower oil does not wrinkle when drying, even with its considerable thickness; the oil dries in a thin layer in the form of cobalt drying oil in about 12 hours. When resins and essential oils are introduced into it, it gives a normal layer of painting; in addition, it can serve as a binder of paints in combination with linseed oil, which moderates the negative sides of linseed oil.
The harsh sentence pronounced by Tauber against poppy oil should also apply to sunflower oil, if we take into account the composition of the latter. One should not, however, lose sight of the fact that poppy oil in the XVII century was apparently successfully used in painting by the Dutch and that from the second half of the XIX century a haphazard method of painting reigned; under such conditions, poppy oil gave, of course, worse results than it could give. With the changed views on the composition of the binders of oil painting, when resins and essential oils were introduced into them, and they also began to use mixtures of various oils, the question of using one or another of the above-described oils as binders of paints remains open to this day, since we still have a long experience with such combined binders in painting we don't have.
For the completeness of acquaintance with various types of fatty drying oils, it is necessary to say a few more words about the following oils.