Cyclopedia of Painting/Oils and Driers
OILS AND DRIERS.
Linseed oil is produced by expression from the seeds, either by hydraulic or steam power. This material varies in quality: According to the goodness of the seed from which it is expressed, and according to its age and clearness; for, when a large stock is kept, it is found that, in about six months, there is a considerable amount of accumulation of refuse at the bottom of the tank, which is only fit to be employed in mixing coarse paint for out-door work. The best is yellow, transparent, comparatively sweet-scented and has a flavor resembling that of the cucumber. Great consequence has been attributed to the cold drawing of this oil, but it is of little or no importance whether moderate heat be employed or not in expressing it. Several methods have been contrived for bleaching and purifying this oil so as to render it perfectly colorless and limpid, but these give it more beauty to the eye, in a liquid state, without giving it any permanent advantage, since there is not any known process for preventing the discoloring after its drying, and it is, perhaps, better upon the whole that this and every vehicle should possess that color at the time of using to which it subsequently tends, so that the painter may depend on the continuance of his tints, and avoid the disappointment and annoyance arising from a change of color.
Linseed oil is sometimes boiled with litharge to make it dry quickly, but when it is thus treated it is unfit for best work.
The quality of linseed oil may be determined in the following manner: Fill a phial with oil and hold it up to the light; if bad, it will appear opaque and turbid, its taste will be acid and its smell rancid. The oil which is expressed from good and full-grown seeds should, when held up to the light, appear clear, pale and bright; it is sweet to the taste and has little or no smell.
Linseed oil may be purified by the following process: Place the oil in a bottle or jar, and drop into it some powdered whiting, stir or shake up the mixture and allow it to stand on the stove, or in an oven, not too hot; the whiting will very soon carry down all color and impurity and form a precipitate at the bottom. The refined oil at the top may then be poured off.
In rare instances, where the least yellowness in the oil would be injurious, nut or poppy oil may be used with advantage; but, as already stated, linseed is the oil used for general purposes.
Oils of a nature suitable for painting are the most commodious and advantageous vehicle to colors hitherto discovered, first, because the unctuous consistence of them renders their being spread and layed on a surface with more evenness and expedition than any other kind of vehicle; secondly, because, when dry, they leave a strong gluten or tenacious body that holds the colors together, and defends them much more from the injuries either of the air or accidental violence than the vehicles formed of water. 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. There are some oils that have this fault to an incurable degree. The next quality in oils is the limpidness, or approach to a colorless state, which is likewise very material; for where they partake of a brown or yellow color, such brown or yellow necessarily mixes itself with the pigments; but, besides the brown color which may be visible in the oil when it is used, a great increase of it is apt to appear some time afterwards when the oil is not good. There are three changes which oils of the kind proper for painting are liable to suffer in their nature, and which affect them as vehicles, that are mentioned by painters under one term, that of fattening; notwithstanding, these several changes are brought about by very different means, and relate to very different properties in the oils.
The first is a coagulation by the mixture of the oil with some pigment improperly prepared. This, indeed, is called the fattening of the colors, but the real change is in the oils and the pigments are only the means of producing it. This change is generally a separation of the oil into two different substances, the one a viscid body which remains combined with the pigments, the other a thin fluid matter which divides itself from the color and thicker part.
This last appears in very various proportions under different circumstances, and, in some cases, it is not found where the pigments happen to be of a more earthy and alkaline nature, for then only a thick clammy substance that can scarcely be squeezed out of the bladder, if it is put up in one, is the result of the fattening. This fattening not only happens when oil and pigments are mixed together in bladders or vessels, but sometimes, after they have been laid on the proper ground for them, instead of drying, the separation will ensue, and one part of the oil will run off in small drops or streams, while the other will remain with the color, without showing the least tendency to dry.
The second is the change that takes place in oils from long keeping. This, if it could be afforded by the oil-manufacturer or the painter, is by far the best method of purifying linseed and other oils, as, by thus keeping, they become lighter colored and acquire a more unctuous consistence; and, though they are said to become too fat, they are in a very different state from that before mentioned, which is caused by unsuitable pigments.
The third is the change produced by artificial means, from exposing the oil a long time to the sun, whereby it is freed from its grosser and more feculent parts, and rendered colorless, and of a more thick and less fluid consistence than can be produced by any other treatment; but, at the same time, it is made less likely to dry, particularly when used with mineral colors, as vermilion, Prussian blue and King's yellow; it likewise becomes disqualified by other bad qualities that render it of little use as a vehicle for painting. Oils in this state are called also fat oils, though it is a change that has not the least affinity with either of the other, but, on the contrary, differs from both. In speaking, therefore, of the fattening of oils or colors, attention should be had to the not confounding these three several kinds one with the other.
Linseed oil, from its cheapness, is the only oil in common use for house painting, and it may, by proper management, be made to answer for every kind of work. This oil is pressed from the seed of flax, and is best when manufactured in great quantities. The general defect in linseed oil is its brown color, and its tardiness in drying, both of which are in a much greater degree found in some parcels than others. There is also found such as, in consequence of its being mixed with the oil of some other vegetable accidentally growing near it, partakes of the nature of olive-oil, and cannot be made to dry by any means whatever. The faults of the color and want of drying quality may be greatly reduced, if not entirely taken away, by keeping the oil for a length of time before it is used; it then becomes fat in the second sense of the word, as before explained, and is a good vehicle for color without any mixture; but it is generally used with a proper drier, as it never by itself becomes sufficiently pure to use with white or other light tints, without imparting a brown color to them.
Poppy Oil. This is a colorless oil, and is in some instances used for delicate works where the length of time required for drying is no object. It is much celebrated in some old books, under the name of oil of pinks and oil of carnations, as erroneously translated from the French œillet, or olivet, a local name for the poppy in districts where its oil is employed as a substitute for that of the olive. It is, however, inferior in strength, tenacity and drying to linseed oil, although next to it in these respects, and, though it is of a paler color, and slower in changing, it becomes ultimately not so yellow, but nearly as brown and dusky, as linseed oil, and therefore is not preferred to it.
Nut Oil is the oil of walnuts, and is used in ornamental painting, as it is nearly colorless, and can be used with flake white and other delicate colors without the slightest danger of tingeing them.
Driers. Driers are used to hasten the drying of paints. These are ground up in oil and are mixed in small quantities with the color; some colors, in fact, will not perfectly harden without them, but remain sticky, or, as painters term it, tacky, until sufficient dust has clung to them to render their external surface at least apparently dry; though, as can be well understood, it will remain disagreeable to the touch and much injured in color. Red lead is a good drier, but, of course, can only be used in situations or in paints where its color is not objectionable. Sugar-of-lead is, however, the best drier, but is more expensive than others. Patent driers, ground up in oil, may be purchased at the various paint stores.
Drying Oils. All the fixed oils have an attraction, more or less powerful, for oxygen, and by exposure to the air they either become hard and resinous, or they only thicken slightly and become sour and rancid. Those which exhibit the first property in a marked degree—as the oils of linseed, poppy, rape and walnut, are called drying oils, and are used as vehicles for colors in painting; the others are termed glutinous or non-drying oils.
The resinifying or drying qualities of the oils are greatly increased by boiling them, either alone or along with litharge, sugar-of-lead or white vitriol, when the product forms boiled oil, or drying oil of commerce. The efficacy of the process depends on the elimination of substances which impede the oxidation of the oil.
The following methods of preparing drying oils are culled from various sources; the quantities of each formula are given as in the originals, but these can, of course, be used in relative proportions when the preparation is to be carried on on a smaller scale.
Linseed oil, 1 gallon; powdered litharge 3⁄4 pound. Simmer, with frequent stirring, until a pellicle begins to form; remove the scum, and when it has become cold and has settled decant the clear portion. Dark colored, used by house painters.
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. It appears probable that litharge acts more by its mere presence in inducing the oxidation of the oil than by actually giving up oxygen to it, and those engaged in boiling oils have remarked that the old litharge, with which linseed oil has been already boiled, acts more energetically in producing the siccative property in it than new litharge.
Pale Linseed or Nut-Oil 1 pint, litharge, or dry sulphate of lead in fine powder 2 ounces; mix, let it stand, frequently stirring it for ten days, then set the bottle in the sun, or in a warm place to settle and decant the clear portion.
Sugar of lead 1 pound, dissolved in 1⁄2 gallon of rain water; 1 pound litharge in fine powder is then added, and the mixture is gently simmered until only a whitish sediment remains; 1 pound of levigated litharge is next diffused through 21⁄2 gallons of linseed oil, and the mixture is gradually added to the lead solution previously diluted with an equal bulk of water; the whole is now stirred together for some hours with heat and is lastly left to clear itself by exposure in a warm place. The lead solution which subsides from the oil may be used again for the same purpose by dissolving in it another pound of litharge as before.
Into linseed oil, 236 gallons, pour oil of vitriol 6 or 7 pounds, and stir the two together for three hours, then add a mixture of fuller's earth 6 pounds, and hot lime 14 pounds, and again stir for three hours. Next, put the whole into a copper, with an equal quantity of water, and boil for about three hours; lastly, withdraw the fire, and, when the whole is cold, draw off the water, run the oil into any suitable vessel, and let it stand for a few weeks before using.
Pale Drying Oil. The oil should be macerated two or three days at least upon about an eighth of its weight of litharge, in a warm place, occasionally shaking the mixture, after which it should be left to settle and clear; or it may be prepared, without heat, by levigating the litharge in the oil. Acetate of lead may be substituted for litharge, being soluble with less heat, and its acid, being volatile, escapes during solution and bleaches the oil, to which coarse smalt may be added to clear it by subsidence, increase its drying and neutralize its brown dolor. This affords pale drying oil for light and bright colors.
Boiled Oil. The above mixture of oil and litharge, gently and carefully boiled in an open vessel till it thickens, becomes strong drying oil for dark colors. Boiled oil is sometimes set on fire purposely, in making printer's varnish and printing ink, and also for painting and the preparation of japanner's gold size. As dark and transparent colors are in general comparative ill driers, japanner's gold size is sometimes employed as a powerful means of drying them. This material may be prepared in the following manner: Asphaltum, litharge or red lead, burnt umber or manganese, finely powdered, of each 1 ounce; stir them into a pint of linseed oil and simmer the mixture over a gentle fire, or on a sand bath, till solution has taken place, scum ceases to rise, and the fluid thickens on cooling, carefully guarding it from taking fire. If the oil employed be at all acid or rancid, a small portion of powdered chalk, or magnesia, may be usefully added, and will assist the rising of the scum and the clearing of the oil by its subsidence; and, if it be kept at rest in a warm place, it will clear itself, or it may be strained through a cloth and diluted with turpentine for use. Gold size for gilding is commonly made of boiled oil and fine yellow ochre.
There is often a difficulty in obtaining the oils bright; after boiling or heating them with the lead solutions, the best way, on a small scale, is either to filter them through coarse woollen filtering paper, or to expose the bottle for some time to the action of the sun, or to place it in a warm situation; on a large scale, the fine oils are often filtered through Canton flannel bags. The litharge and sulphate of lead used in the above processes may be again rendered available for the same purpose by washing them in hot water to remove the adhering mucilage.
Drier for Zinc White. Purified linseed oil is boiled for six or eight hours, and to every 100 pounds of boiled oil there are added five pounds of powdered peroxide of manganese, which may be kept in a bag like litharge. The liquid is boiled and stirred for five or six hours more and then cooled and filtered. This drying oil is employed in the proportion of from five to ten per cent of the weight of zinc white, and it should be added during the grinding of the pigment in oil, the admixture then being more thorough.
Drying Oils. Fifteen parts of lime made into paste with water are added to 100 parts of oil oxidized by peroxide of manganese. The whole is boiled or heated by steam until the water has evaporated; the oil then forms with lime a thick product which is a drier. It may be ground with the ordinary oil of turpentine, or with that of Venice, but the dryer is less powerful than when it has been mixed with oxidized linseed oil. Three to five per cent of this drier are sufficient for a rapid desiccation.
Other driers may be made by combining lime with resins and essence of turpentine in the proportions indicated for fixed oils.
Powdered Drier. Pure sulphate of manganese 1 part, pure acetate of manganese 1 part, calcined sulphate of zinc 1 part, white oxide of zinc 97 parts. The sulphate and acetate are ground in a mortar to an impalpable powder, which is passed through a metallic sieve. Three parts of this powder are dusted over the 97 parts of oxide of zinc, spread over a board or a slab; the whole is then thoroughly mixed and ground. The resulting white and impalpable powder, mixed in the proportion of 1⁄2 to 1 per cent with zinc white, will enormously increase the drying property of this product, which will become dry in from ten to twelve hours.
Volatile Oils, procured by distillation from turpentine and other vegetable substances, are almost destitute of the strength of the expressed oils, having hardly more cementing power in painting than water alone, and are principally used as solvents, and media of resinous and other substances introduced into vehicles and other varnishes. In drying they partly evaporate and partly, by combination with oxygen, form resin and become fixed. They are not, however, liable to change color like expressed oils of a drying nature, and, owing to their extreme fluidness, are useful diluents of the latter; they have also a bleaching quality, whereby they in some degree correct the tendency of drying and expressed oils to discolorment. Of the essential oils, the most volatile and nearest in this respect to alcohol is oil of sassafras, but that most used in painting is the rectified oil, improperly called spirits of turpentine, preferable only on account of its being thinner and more free from resin. By the action of oxygen upon it, water is either generated or set free, and the oil becomes thickened, but is again rendered liquid by a boiling heat upon water, in which the oxygen and resin are separated from it. When colored by heat or otherwise, oil of turpentine may be bleached by agitating some lime powder in it, which will carry down the color. The great use of this oil, under the name of turps, is to thin oil paints, and, in the larger use thereof, to flatten white and other colors, and to remove superfluous color in graining. It, however, weakens paint in preventing its bearing out, and when used entirely alone, it will not fix the paint.
The name of turpentine is applied to a liquid, or soft solid product of certain coniferous trees, and of the Pistachia terebinthus.
There are several varieties, as follows: American or white turpentine, Bordeaux turpentine, Venice turpentine, Strasburg turpentine, Canadian turpentine, or Canadian balsam, Ohio turpentine and Frankincense.
In nearly all cases the processes of collecting are similar. A hollow is cut in the tree yielding turpentine, a few inches from the ground, and the bark removed for the space of about 18 inches above it. The turpentine trickles down into vessels placed to receive it. The incisions are made about the close of March, and the turpentine continues to run throughout the vegetative season, especially during the summer months. In general character these turpentines have much in common; they are oleo-resins, varying slightly in color, consistency and smell; they enter into the composition of many varnishes.
Oil of turpentine is obtained by distilling American turpentine, which has been melted and strained with water in an ordinary copper still. The distilled product is colorless, limpid, very fluid and possessed of a very peculiar smell.
The residuum, after the distillation of the oil or spirits of turpentine, is the common resin of trade.