الزيوت والراتنجات والمواد الأسفلتية ١_a , من كتاب تكنولوجيا التصوير د.م محمد حماد

- Oils, resins and asphalt materials

Types of oils:

Oils are usually divided into three types:

1- Fatty oils that are not subject to drying, such as oils used for food, such as olive oil, French oil (cotton seed oil) and castor seed oil. They are not used in oil painting as a mediator when preparing colors... However, they are sometimes used in the manufacture of colors. Some manufacturing companies Colors It is preferable to add a small percentage of them to make the colors slow drying, so they do not oxidize quickly from the effect of oxygen in the air.

2- Natural oils that have the property of dehydration. This type of oil, in turn, is divided into two parts in terms of the speed of drying. Some of them are slow-drying, like linseed oil, and some are quick-drying, like poppy oil. From these oils or combinations of them, oil colors can be prepared.. However, these are the best types

Oils for preparing colors for artwork is linseed oil 3- Tabbara natural oils such as vegetable turpentine oil that is used in

Color dilution.

And natural oils that have the property of dehydration are formed from the union of acids

Unsaturated fatty acids with glycerin, meaning that they are unsaturated fatty acid glycerides, called in French (Triglycerides d'acides gras non satures). . The ability of the oil to dry always depends on the degree of saturation in its molecules (1).

(1) If the oil molecule contains only one double bond, it is non-drying. If the oil molecule contains two or three double bonds, or a mixture of them, the oil is capable of drying, so if the oil is exposed to air for a sufficient time, it absorbs oxygen from the air in the double bonds, then the molecules crystallize, or the polymerization process takes place and compounds that have multiples of molecular weight are produced, or they form larger molecules. It has a greater weight, with an increase of about 28.7%. The strong substance that consists of the confirmation of linseed oil and its polymerization is called lytoxin (Palymerisation).
Litharge (Oxyde de cobalt) If the flaxseed oil is exposed to the air for a sufficient period, it absorbs oxygen from the atmosphere and is sure, thus preparing for dryness and immobility. Heating at a temperature of more than 200 degrees Celsius helps to speed up the oxidation process, and thus a level oil is formed. Also, to speed up the preparation of level oil, oxygen or air is pressurized inside the oil to pass through it in the form of bubbles that permeate the liquid, so it works on the speed of compaction, or this can also be done with the help of Chemical substances such as the presence of certain lead (lavilar) or manganese dioxide (Bioxyde de manganese) or cobalt oxide or cobalt acetate (Acetate de cobalt). Industrial, such as pepper or heating with the addition of chemicals, make the oil quick-drying, always at the expense of the properties of the oil itself, as the oil loses some of the properties of the fatty substances contained in it... In addition, the presence of chemical deposits in it is the greatest danger to the imaging colors themselves... Therefore, we must always repeat that the best oils are what were prepared by simple natural methods, which preserve the original properties of the oil even if the colors prepared from it need a longer period of drying.

The most important natural oils that have the property of drying

(Linum usitatissimum) For artists' oil painting, we find that the oils that are used are the oils that have the property of drying because they clarify the color and preserve it and have the ability to stay for a long time... The most important of these oils and the most used among photographers is flaxseed oil, known as raw oil, and it is extracted from the seeds of a plant Flax) and its scientific name, and it is grown in a grate since ancient times. It is also grown in temperate regions of the world. The flax plant contains about 25% of the oil, and this percentage varies according to the areas in which it is grown in relation to its climate and soil fertility. Linseed oil is extracted from the seeds after grinding and cold pressing.... However, the preferred oil for painting is the oil extracted in the first batch (first harvest) by the cold pressing method, and we find that its color is whitish to yellowish, and it has a pleasant smell that easily distinguishes it from the extracted juice. In the second batch (second picking), which is extracted by the hot pressing method, its color tends to be yellow-brown.

There are, of course, many vegetable oils that can be used... However, the best oils that come after linseed oil are in the rank for artists, because they are suitable for the artistic work that they do, in terms of ability and sufficiency. They are:

Walnut oil

L'huile de noix

Poppy seed oil

L'huile de pavot
And because of its importance, we will discuss it after that, and we will talk about the methods that are used to purify it from impurities, so that we can find from the crude oil an oil that is suitable for photography and does not contain sediments that affect the colors - no matter how small they are, especially if these impurities contain some chemical deposits, which must be warned by every artist .

These crude oils are used raw and pure... They can also be treated with special treatment such as boiled oil (level) which changes some of its properties and is used in oil paints... However, it is not good to use it in artistic oil painting works, and therefore photographers prefer to treat oil in the natural way Which was used in the works of the old great photographers, by filtering the oil and exposing it for a long time to sunlight ... because this helps the speed of oxidation ... and the purity of the oil increases by absorbing the oxygen present in the air without the oil losing anything of its creamy fluidity that helps move the color in it and knead it easily .. It reflects what is done by the industrial method that increases the density of the gels in the oil, which is like fur and prevents the brush from moving easily in the color paste.This simple natural method of treating oil, which has been used throughout the ages, is still practiced until now.

There are some oils offered in the market that are prepared for use, and they have been treated with the addition of some chemicals that speed up their drying, as we have previously explained, and they are used in industrial work such as coating some small pieces of art, or they may be used in some paints... But these industrial oils are not It is suitable for artists’ oil paintings, and the painter, if he wants to use these oils in artwork, must note that they are not old, and they must also be of a high degree of purity, and they should be used in the amount required for the composition of colors, and it is better not to leave them for a long time in the open before using them. Do not dry out or become unusable.

1- Flaxseed oil:

It is the most common and used oil for a long time now. And this is not due to its fluidity, which works on flexibility in its use, resistance, and its ability to survive, we think... but also because it does not change its color, so it blackens or cracks (1). Colors mixed or dissolved in linseed oil blend over time and are not erased

This is unlike what may happen in other oils. And there

And don't crack

(1) These are the properties of flaxseed oil.. To test its strength, put in a test tube 10 cm of silver nitrate 25 and add 5 cm of the oil to be tested, then add some nitric acid to the mixture and fry it on the fire in a water bath for several minutes, and notice If the oil is vomited, it retains its colour, texture and smell and does not change. Otherwise, it is mixed with refrigerator or other oils.