Drying oil

“ They are viscid and of a pale yellow color, lighter than water, and therefore float upon it, and are very combustible. Oils are used for a multiplicity of purposes: for burning in lamps, for making paints and varnishes, preventing the friction of machinery, in making soap, and numerous other processes. Oils are generally divided into fixed and volatile oils; as an example of the first, linseed oil may be selected; of the last, oil of lavender.
Some of the fixed oils are called drying oils, and it is this kind that are used for varnish making ”

“ It is well known that the time of drying and the condition of the dried film of any oil or mixture of drying or semi-drying oils will vary widely. It is for the purpose of causing oils to set up to a hard film in a short time that metallic driers in the form of salts of manganese and lead, soluble in oil, are added to a paint. Some oils require a large amount of drier, while others require only a very small amount. Those which require a large amount are apt, upon exposure, to be burned up by the drier, resulting in the formation of a powdered and disintegrated film. ”

“ Although solidification of a drying oil charged with manganese takes place in from 5 to 6 hours when spread in thin films, the solidification of thicker films requires a longer time. A temperature of 122° to 140° F. accelerates the oxidation of the drying oils, partly because the oil becomes more fluid, and partly because the oxygen is more active at a higher temperature. Hence, oil which has been mixed with an equal volume of turpentine, or a light hydrocarbon, such as benzene, dries more rapidly than oil without such admixture. ”

“ Little is known respecting the chemical reactions which take place during the boiling of oil. Even when the air is excluded during the process, the drying properties are greatly increased, and, if boiled long enough, the oil is converted into a solid substance. The loss of weight which ensues is dependent upon the temperature and the time during which the operation continues. It is less when the air is freely admitted than if the pan is covered with a hood. The vapours given off by the oil are of an extremely irritating character, and should be destroyed by passing them through a furnace. ”

“ Linseed oil dries too slowly for general use by the painter, hence various ways have been devised to hasten the drying process. If the foregoing theory is correct, the process which will cause the oil to dry to a good wearing body in the time desired, and leave it in the best condition to resist the action of the elements and the absorption of oxygen, is the best. ”

“ When we add an oxide to linseed oil as a dryer in the small quantity which experience has taught us is best to use, it is evident that it is not sufficient in itself to oxidize the whole of the oil to an appreciable extent. Writers differ as to the peculiar action of the oxides upon the oil, but I think it safe to say that the dryer sets up some chemical reaction which increases the affinity between the linolein and the oxygen of the atmosphere; at any rate, there is no dispute upon the point that linseed oil in drying absorbs a large per cent. ”

“ By the action of chlorine produced in contact with the oil when, for instance, an aqueous solution of bleaching powder is acidified with a cheap mineral acid, such as dilute sulphuric. In this case rapid mixing and violent agitation are essential to the success of the process, otherwise chlorinised products are retained in the oil, which not only confer upon it a distinct flavour and odour, but also cause the oil to solidify with a very moderate lowering of the normal temperature. It is very questionable whether drying oils can with advantage be submitted to such treatment. ”

“ Adulteration of linseed oil with mineral and other non-drying oils, has a tendency to make paint dry soft. Linseed oil, kept for a few days in an old sour tank or in an old rancid can in the paint shop, is liable to cause fermentation to take place, which may result in mildew in damp weather in shaded places.
When an oil can smells sour, or there is a deposit of foots at the bottom, it is unfit to keep oil in. ”

“ Fixed oils are extracted by pressure from vegetable substances, they are of a fatty nature, do not evaporate in drying, and will bear a temperature short of 500° Fahr., without decomposing. They are subdivided into drying oils, which become thick upon exposure to air. Of these, linseed oil is most commonly used as an ingredient for paint. Its qualities when pure are excellent, and it may be considered the best of all oils for use in paint, putty, and other similar substances. It oxidizes and becomes thick upon exposure to the air. ”

“ The wax may be replaced by paraffin wax with advantage.
It is desirable to be able to ascertain whether the oil intended for use is, or is not, adulterated with non-drying oil. The distinction of non-drying oils is that they solidify when acted upon by peroxide of hydrogen, or by sub-nitrate of mercury—the oleic acid is concreted, and a substance called elaidin is formed. This does not take place with the drying oils.
The oils used in paint making are chiefly—
Ground-nut Oil.—The ground-nut or pea-nut (Arachis hypogæa) is very widely cultivated in the tropics for the sake of its oily seeds. ”

“ Three hours boiling, with litharge one-tenth in weight of the oil, renders the oil more perfectly drying than when the boiling is continued for a much longer time, when the oil acquires a darker color and so becomes injured in transparency the longer it is boiled. Merely heating linseed oil to 170° Fahrenheit, along with a small quantity of peroxide of manganese, as completely renders it siccative as any amount of boiling, and without any deterioration to its color or transparency. ”

“ Hempseed oil is a mean tasting, mean smelling, but good drying oil, and only because of its rapid color changes, wearing finally to a dull brown, is its employment in linseed oil restricted to narrow limits. ”

“ Vehicle is the diluent used to temper and thin the colors for the purpose of bringing them to a proper state. Linseed oil, rendered drying by boiling with certain metallic oxides, is the vehicle generally used. Drying oil should dry quite free from stickiness in two or three days, in ordinary weather. Copal varnish is also an excellent vehicle, but dries so rapidly that it will not do where the colors require considerable manipulation with the brush—as in skies and broad tints generally. Colors used with varnish will require frequent thinning with spirit of turpentine. ”

“ Its odour is strong and peculiar, and recalls to those who are familiar with it the smell of bitumen and naphtha. Exposed for a long time to the air, it does not thicken or form a skin on its surface, and in no sense can it be called a drying oil. The density of the crude oil is .882, water being 1.000. It boils only at a very high temperature, and yet it begins to give off a vapour at a temperature not greatly above that of boiling water. It takes fire with some difficulty and burns with an abundant smoky flame. ”

“ These oils when mixed with drying oils and strong driers find application in the manufacture of some freight-car, barn, and other paints which sell at a low price. A small percentage of mineral oil is said to be valuable in structural steel paints, acting as a preventative of hard drying and thus keeping the film soft and elastic. Streaking and sweating is apt to ensue if any great quantity is used. ”

“ The dung, by a kind of fermentation, accelerates the oxidizement, and hence crude oil is preferable to pure. In England, the mucilaginous oils of Gallipoli are preferred, and in Malabar, oils more or less rancid. The drying oils do not answer. The subsequent treatment with the alkaline liquors removes the excess of oil, which has not been oxidized and combined; a hard drying completely changes that which remains in the fibres; the aluming which follows combines alumina with the cotton; the galling tans the fibres, producing a triple compound of oil and alum, which fixes the colouring matter. ”

“ The principal and most general quality to be required in oils is their drying well, which, though it may be assisted by additions, is yet to be desired in the oil itself, as the effects of the pigments used in it are sometimes such as counteract the strongest driers, and occasion great delay and trouble from the work remaining wet for a great length of time, and frequently never becoming thoroughly hard. ”

“ An oil, generally linseed or poppy oil, which is ground up with the white lead or zinc-white until it becomes a soft paste. This is mixed with variable preparations of linseed oil and spirit of turpentine.
(3) A substance called dryers, or siccative materials; it may be linseed oil in which litharge is dissolved, or it may be linseed oil containing a compound of manganese.
Paint owes to the dryers its property of drying more rapidly than it would do without it ”

“ It is superior in drying powers, tenacity, and body to any other fixed oil. The best oil comes from the Black Sea and the Baltic; that from the East Indian seed is inferior, as the seed is less carefully cleaned, and contains too much stearine. Raw linseed oil is clear and light in color, works smoothly, and is used for internal works, for delicate tints, and for grinding up colors. Boiled oil is much thicker, darker, and more apt to clog. It is used for outside work, as its greater body and rapidity in drying make it a quicker and more efficient protection. ”

“ The best driers are those which contain a large proportion of oxygen, such as litharge, acetate of lead, red lead, sulphate of zinc, verdigris, etc. They are sometimes used to improve the drying qualities of the oil with which the paint is mixed, or they may themselves be ground up with a small quantity of oil, and added to the paint just before it is used. ”

“ There is no advantage in heating the oil to a higher temperature than 350° F. Accurate experiments have shown that the drying properties of the oil are not increased by heating it beyond this point, while its colour is considerably darkened.
For the finer qualities of boiled oils, it is essential that the raw oil should have been stored for some time, so that it may be free from mucilage. This mucilage is the chief source of the dark colour of some boiled oils; when heated, it forms a brown substance, which is soluble in the oil itself, and extremely difficult to remove. ”

“ In reality, however, there are but three kinds—coach japan, specially adapted for colors to be quickly dried and containing no oil; liquid drier (or dryer) intended for the drying of oil and oil paint; and patent driers purchased in paste form, effective only when used in conjunction with oil. ”

“ They are neither of them quick dryers, and are usually mixed with sugar of lead, manganese, etc., to hasten the drying. These have a tendency to affect the colors; but if one will have recourse to none but the pure oils, he must be patient with the drying of his picture. For this reason it would be well to use vehicles with the colors on the palette as little [Pg 62] as possible—and that is against thin and smooth painting.
Oil has the tendency to turn dark with time, thus turning the color dark also. The only way to reduce this tendency is to clarify the oil by long exposure to the sunlight. ”

“ Extreme heat is dangerous to oil at all stages of expression and storage; and for this reason Italians doubt the safety of artificial drying even where they consider drying necessary or advantageous. After the expression of the oil, it separates from the water and small particles of the berry which have passed the sacks or cage, and rises to the surface, when it is carefully skimmed off and placed in other vessels to settle ”

“ As delivered from the drying apparatus, the wool is bright and clean, but somewhat harsh and wiry to the touch, owing to the removal of the yolk which is its natural lubricant. To render it soft and elastic, and to improve its spinning qualities, the fiber is sprinkled with lard oil or olive oil. As the oil is a costly item, it is of consequence that it be equally distributed and used economically. To attain this end various forms of oiling apparatus have been invented, which sprinkle the oil in a fine spray over the wool, which is carried under the sprinkler by an endless cloth. ”

“ Although several grades of oil termed crude, brown, light, etc., are produced, the most satisfactory for use in paint is that grade termed “light winter pressed.” This oil is of a pale straw color and has a high iodine number which is responsible for its rapid drying value. It contains less of the stearates that precipitate from crude oil, but sufficient to render its film water-shedding and elastic. The presence of too great a quantity of stearates is apt to result in a [14] very soft film, and the use of hard driers, such as the metallic tungates, is therefore advisable with menhaden oil. ”

“ Oil absorbs oxygen in drying, and so is apt to have an effect on colors liable to change from that element, and many vehicles contain materials to hasten the drying which further aid in the deterioration of the pigment. Bad oil will tend to crack the picture also. ”

“ For ‘flatted white,’ &c., the colour being ground in oil, requires scarcely any further addition of that article, as the object is to have it ‘dead’ or dull. The best driers are ground litharge, and ground sugar of lead; the first for dark and middle tints, and the last for light ones.
To preserve mixed paints in pots from ‘skinning over’ or drying up, they should be kept constantly covered with water; or, what is better, with a thin film of linseed oil. ”