Vegetable Oil Paints L. L. CARRICK, University of Michigan, Ann Arbor, Michigan HE Egyptians recognized the inedicinal proper- table waxes, pitches, or the oils from wild nuts or T ties of linseed oil but were unacquainted with its seeds. The early use of raw walnut, linseed, poppy drying properties. Ludius used oil in encaustic seed, olive, or hcmpseed oils has been noted together paints during the reign of Agustus (63 B.C.-14 A.D,). with the advent of their refined and bleached modifi- Vitruvius, during the same period, prepared a var- cation. Chinese tung oil, according to D'Incarville, nish from Punic wax and a little oil. Dioseorides 1735, was first a common adulterant of Chinese lac- (69-30 B.C.) recognized the dispersion properties of quers and did not commercially replace linseed oil in oils for natural resins. Pliny the author (A.D. 23-70) many varnishes in the United States until 1900. makes no mention of the use of oil by artists or Enamels were unknown before the beginning of the painters. Lucanus (A.D. 37-68) mentioned the use present century. Prior to this time it was common of oil to improve the working characteristics of color practice to apply a flat oil paint of the desired color for paints. Galen (A.D. 131-200) coagulated drying and follow it with a coat of clear varnish to obtain oils, such as hempseed, nut, and linseed oils by means the needed gloss. About this time it was found that of litharge, white lead, and umber. Actius (A.D. pigments could be ground into a varnish vehicle a~d 540) emphasized to the arts the drying properties give a product which was stable in the container. and varnish potentialities of linseed, castor, and nut This product would give in one operation a film of oil used by Gilders and encaustic painters. Lucca the desired color which had high gloss and good (A.D. 800) was the first to record instructions for levelling. preparing varnish from resin and boiling linseed oil. The commercial use of perilla, fish, soybean, oiti- In the 11th century Theophilis, a monk, gave explicit eiea, sunflower, safflower, and dehydrated castor oil instructions for melting resin until clear, adding hot in paints are attributed to developments in the 20th linseed, olive, walnut, or poppyseed oils and continu- century. ing to heat the mixture until a drop remained clear Such paints or metal primers, sanding undercoats, upon cooling. He complained about the slow drying baking colored enamels, and oil stains are among re- characteristics of the fihn and resorted to exposure cent developments required by the industrial ad- to the sun to accelerate drying. In principle this is vances of a mechanical age and the tremendous the same method employed at the present time in increased demand as a result of shortened production many varnish cooks. schedules, production lines, and increased market Eraelius and Petrus (12th to 13th centuries pressure. A.D.) recorded methods for the extraction and re- fining of oil by adding small quantities of lime, fol- Although modern scientific studies have uncovered lowed by heating and continued skinning. Petrus and developed many substitutes and partial replace- also used white lead as a drier and bleached oils in ments for drying oils, it has not been able to decrease the sun with frequent agitation. The protective value their importance to any appreciable extent. Today's of drying oils was generally accepted in France, paint and varnish industry and many synthetic resin England, and Germany in the 13th and 14th cen- industries would be greatly handicapped if forced to turies. Jacobus de Tholeto, 1450, was among the first formulate the variety of modern organic protective to suggest that metallic salts be cooked with the resin coatings industrially, without the aid of the oil prod- and oil to hasten the subsequent drying rate. No men- ucts of nature. tion of thinning varnish was made until 1736, when There are a large number of factors which have Alberti of Magdeburg thinned varnish with turpen- great influence upon the utility of organic protective tine, which remained the principal thinner of varnish coating oils, any one of which may spell the difference until 1880 after which petroleum distillate was com- between usability or be completely or largely respons- mercially employed. Watin, 1773, realized the com- ible for the oil's unusability. These factors may be mercial possibilities of varnish and published a book roughly grouped into two categories, technical factors in which he offered varnish for sale to other crafts- and economic factors. men so that they would not have to cook their own The economic factors, in turn, are dependent upon varnish. In the 13th and 14th centuries the records such subfactors as steady availability of the oil, sta- show that Liibeck, Kolmar, van Eyek, Cennini, A1- bility of the oil supply, physical and chemical stabil- eherius, and other artists and craftsmen demonstrated ity of the oil, low price of the oil, and stability of the the value of common oils, such as raw and refined price. The technical factors may be further divided walnut, linseed, hempseed and poppy seed, for use as into the properties of the liquid oil and the properties vehicles in portrait and decorative paints. At Canter- of the drying or dried oil film. A few of the liquid bury (13th century) and Ely (14th century) the oil properties which must be evaluated in terms of records disclose that oil was used in decorative paints. the formulation requirements are acidity; color~ Oil was first used commercially in the manufacture odor ; viscosity ; ~amount of saturated fatty acids; of varnish in England in 1790, France 1820, New amount of unsaturated fatty acids; degree and ar- York 1828, Germany 1830, and Austria 1843. rangement of the unsaturated double bonds in the The date of the first use of oil in paints has been fatty acid; drying rate and time; solubility in com- lost in obscurity. The earliest paints were little more mon solvents; miscibility with other oils; skinning than colored rock or clays dispersed in plant juice, time, stability in storage; stability under heat, flow, milk, egg white, natural glues, animal and/or vege- leveling, break, and wetting characteristics. 513 514 TIIE JOURNAL OF THE AMERICAN 0IL CHEMISTS' SOCIETY, NOVEMBER, 1950 Purpose oil film. Important in all films where unprocessed oils are used and may be important in many processed oils. It is the purpose of this paper to point out the oils 8. Some fihns of oil, more than others, show as a result of that are used in today's organic finishes. We will continued reaction in the oil film, after it sets, a decided confine most of our discussion to the consideration of tendency to yellow. They are said to have bad color retention. the direct applications to paints and not unduly em- The type of unsaturation and the amount of the unsaturates are important in estimation of the change in color in varnish, phasize the important and widespread uses of oils in lacquers, paints, and enamels, especially white and tints. the manufacture of varnish and synthetic resin, ex- 9. Oils which are blown with air at 200-400~ for several cept where their products are used in paints. We hours show the effect of oxygen attack on the double bonds by shall briefly call attention to the composition of the an increase in viscosity, deepened color, low solubility in non- polar solvents, and greater reactivity with basic pigments. oils so as better to appreciate the uses of oil whether Blown oils have reraarkable wetting characteristics but are in it is raw, refined, treated, modified, improved, or many properties inferior to kettle bodied oils. synthetic. 10. Oils which are heat bodied in the absence of air show In the fihn the dried oil properties such as hard- a gradual increase of viscosity which eventually leads to a solid gel where the oil molecules are united at the double bonds ness, flexibility, elasticity, resilience, color, color through primary valences without any intermediary oxygen retention, permeability to fluids, waterproofness, ad- linkage. These oils show improved properties over those of hesion, solubility, resistance to ultraviolet light, the raw oils. These oils have better flow and leveling char- resistance to acids and alkalies, gloss retention, bleed- acteristics. The fihns dry harder and faster. The films are glossier and generally have improved resistance to the weather ing, resistance to heat and abrasion, transparency, and wear. The bodying of the oil permits the addition of coefficient of expansion for conditions under which volatile thinner without unduly lowering the viscosity. used, and other properties for specific application 11. The raw oils may be used without the addition of undue must be met if the oil is to meet with wide-spread amounts of volatile thinners. 12. Many raw oils are unusable without kettle treatment favor. The continued use of oil in a paint vehicle or blending. without doubt must reflect the fact that the above 13. Evidence points to the mixed triglyceride molecular mentioned economic and technical factors have in a structure of drying oils. A mixed triglyceride structure gives, large measure been met. With few exceptions science during fihn formation, a more homogeneous structure to the film and improved characteristics among which are waterproof- has found other materials than oil, which excel in hess and wear. one or more of the liquid or film properties, but these 14. The general utility of the oll is dependent upon the competitive materials are deficient in other character- number of fatty acids which enter into the structure of the istics, and, in addition, lack the ability to meet the mixed triglyceride molecules in any oil.