PAINT DRIERS DISCUSSED IN 19TH-CENTURY BRITISH OIL PAINTING MANUALS
3 ARTISTS' USE OF DRIERS
Thus far, the presence of driers in the commercial preparation of painters' oil and in drying oil has been detailed. In addition, a separate product was sold in bladders and tubes to be used by artists as they prepared their palettes. One early account (Fielding 1839, 71) of this prepared drier indicates that it was a mixture of lead acetate and oil:
Acetate, or sugar of lead, ground with boiled oil, poppy, nut, or linseed, can scarcely be called a vehicle, being merely used to force the slow-drying colors, such as Vandyke brown, Blacks, & c. to dry when frosty or cold weather prevents this very necessary operation from proceeding at the same rate with colors of better qualities. This mixture should be ground exceedingly fine, by which its desiccating properties are greatly increased. It is kept in bladders [and “metallic tubes” was added in the 1846 edition of this book] at all the color shops, and known by the name of “drier.”
Artists' colormens' catalogs regularly included sugar of lead or sacrum (synonyms for lead acetate) among their lists of oil tube colors; it is likely the “drier” referred to in the above quotation.
3.1 LEAD ACETATE
Aside from being available from the colormen presumably mixed with oil, lead acetate powder was sometimes used by itself, either being ground with oil and pigments or added to the painting medium. For example, one artist-author, Julius Caesar Ibbetson, recommended adding anywhere from one-sixth part up to equal amounts of lead acetate according to the pigment used (table 1).
TABLE 1. THE ADDITION OF SUGAR OF LEAD TO PIGMENTS
Field (1835, 57) remarked that artists “strew their pictures while wet with the acetate of lead,” and although he decried this practice, later in the same work he suggested that a weak solution of lead acetate in water might be brushed over the ground prior to painting to enhance drying in damp weather.
Of all the metallic compounds available as driers, lead acetate received the most attention in the sources. Like most detailed information on materials, this was confined mainly to books published before 1850.
Lead acetate had apparently been widely available in Britain since the 18th century. In 1758, Robert Dossie (1:152) provided instructions for making lead acetate from vinegar and metallic lead but noted, “It is to be had so constantly, and at so much less expence [sic] at the shops of chemists and druggists, than it can be made in small quantities, that is is needless to give any more particular recipe.”
Nevertheless, authors did caution artists on the quality of lead acetate to use: they noted that if it was to be used in the preparation of an oil varnish, it should be prepared from white lead rather than from litharge, since the latter contained impurities that could hamper the purity and transparency of the varnish (Neil 1833, 55). Artists were also warned that they should ensure the lead acetate had been dried before use and was afterward stored in an air-tight container because it was apt to pick up moisture from the air (Neil 1833; Cawse 1840). Others recommended that the basic lead acetate should be used rather than the more acidic variety, which was generally more pure and crystalline. To make the purest and most acidic variety more alkaline, one author advised adding litharge; this way it would be more effective and safer to use in oil (Field 1850).
Information from the 19th-century texts can in part be related to modern descriptions of lead acetate. Its molecular weight, melting point, crystallinity, and solubility vary considerably according to its method of manufacture. The basic salts formed are neutral lead acetate, basic lead acetate, lead acetate trihydrate, and lead tetraacetate. Lead acetate made from lead carbonate, or white lead, which Neil (1833) had recommended using, would likely have resulted in neutral lead acetate. Judging from the descriptions in the 19th-century sources overall, the lead acetate used was neutral, basic, or lead acetate trihydrate (Kirk-Othmer 1981).
Nineteenth-century authors noted that the more finely ground in oil, the better lead acetate's drying properties, and many recipes recommend dissolving it first in water. A number of sources warned that lead acetate should not be used in its crystalline or granular form, since as one early 19th-century author remarked, it will “ultimately effloresce on the surface of the work, and throw off the colour in sandy spots” (Field 1835, 56). This same phenomenon was described in a late 19th-century source:
I have seen one of the results of this commingling of sugar of lead with the medium or the paint in the production of an immense number of small spots in the picture, sometimes appearing through the surface varnish in the form of a white efflorescence (Church 1890, 94).
A modern description of neutral lead acetate confirms that it slowly effloresces but notes that it becomes “incompletely soluble” as it takes up carbon dioxide from the air, which implies that its propensity to effloresce may change in time (Budavari et al. 1989, 851).
Other authors warned, in more vague terms, that lead acetate may “injure the colours.” However, leading authorities such as Sir Charles Eastlake and George Field agreed that problems with this material were related to its use in excess. Eastlake (1847, 1:350) wrote, “The extreme case of its [lead acetate] visible efflorescence can only occur when it is used in unnecessary abundance,” although he did note, “The use of acetate or sugar of lead is further dangerous, on account of its tendency to recrystallise, thereby rendering the transparent colours dull.” In his copy of Eastlake's first edition (now in the Canadian Conservation Institute Library), Field added a handwritten comment to this section, “The objections against it arise chiefly from using it in excess.”
It is important to note that lead acetate may also have been present as an intentional addition during the manufacture of artists' materials. For example, one 19th-century source complained that up to 3% lead acetate was being added to artists' white-lead paint. The reason, oddly enough, was to keep the white “from growing hard in the tubes” (Scott Taylor 1890, 40). This author was writing in 1890; whether that practice had begun much earlier is not known.
This curious reversal in the use of lead acetate to retard drying had been recommended by Ibbetson (1828) for vermilion. He advised that nearly an equal quantity of lead acetate should be added to vermilion because “the sugar of lead prevents the vermilion from becoming hard.” The only possible explanation for this was alluded to by Field (1835), who noted that an excess of drier would inhibit drying.
3.2 LEAD DRIERS AND GELLED MEDIA
Lead compounds were popular as driers because they were cheap, available, and the most effective. However, there was another very important reason why lead driers were favored: lead-treated oils, in the presence of certain resins, will gelatinize. This property was exploited to form gelled painting media that would influence the handling properties of the paint. These buttery transparent gels were used to enhance the paint's brushability and to achieve transparency (Carlyle 1991, 1).
Megilp, the best known of the gelled media, was made by mixing drying oil (prepared with lead) and fairly concentrated mastic varnish. The ratio was usually either 2 parts oil to 1 part varnish or an equal mixture of both (Townsend et al. 1998). A variation of megilp that was initially known as “gumption” was sometimes called white megilp. In its original form it was made by grinding lead acetate powder and mastic resin in linseed oil. Although subsequent recipes varied, this medium was usually distinguished by the use of lead acetate (instead of other lead compounds) with otherwise untreated oil. According to the 19th-century authors, the advantage of lead acetate was that it could be added to the oil without heating and would therefore result in a less-colored product.
Recipes for megilps were provided in the sources throughout the century, and these products were also available ready-made from the colormen. One of the most popular was a formulation sold by the artists' colormen Roberson and known as Roberson's Medium. To ensure that the more intractable resin, copal, would form a gel, this recipe specified a copal oil varnish that had been boiled a second time with extra red lead and litharge, and mastic varnish was included in the recipe (Roberson recipe, transcribed in Carlyle 1991, 2:338).
3.3 GLASS AND SMALT
The author of a 17th-century oil painting manual noted that “the whitest glass” ground to an impalpable powder would “dry all Colours without drying Oyle, and not in the least Tinge the purest Colours, as White, Ultramarine, &c. and is much us'd in Italy” (Smith 1693, 73). Two sources close to the turn of the 19th century mentioned that powdered crystal (leaded-glass) was an effective drier (Practical Treatise 1795; Compendium 1808). In 1835, Field (81) noted that yellow orpiment was believed to be affected by the use of oil treated with lead driers and that “levigated glass” had been used instead as a drier. Smalt, too, was held to be a strong drier, and on that basis one author recommended that 1/20 part of smalt was to be added to ultramarine in the winter to assist its drying (An American Artist 1845). References to the use of powdered glass or smalt as driers were not found after 1845.
There is one other category of driers that became available commercially to British artists in the last half of the 19th century. These were the “siccatifs” such as Siccatif de Courtrai and Siccatif de Harlem.
Siccatif de Courtrai was described as a powerful drier: one source warned artists away from its use since it was “a very dangerous mixture, heavily loaded with compounds of lead” (Church 1901, 111). Vibert (1892, 83) considered it “dangerous” because Siccatif de Courtrai contained turpentine and therefore tended to be used like a diluent, encouraging artists to use excessive amounts. Siccatif de Harlem, was based on copal resin and, according to Vibert (1892), contained only oil of spike with the copal. It apparently produced a hard, brilliant, and tough film and could be used either as a medium or a varnish. From the description of its applications given in a Lechertier, Barbe & Co. catalog from 1879, it sounds similar in use to a medium. Although intended to function as a drier, descriptions of Siccatif de Harlem indicate that it was simply a resin. Vibert (1892) explained that it only appeared to help the paint dry through its own evaporation and, unlike a true siccative, did not provide oxygen for the oil.
3.5 VARNISHES AND THE RESINATES
There are a few occasional references to the use of varnishes to assist the drying of paint. One author had described a mixture that was predominantly mastic resin with a small proportion of nut oil and alum meant to act as a drier for ultramarine and the lakes (Merimée 1839). In addition, there was another class of driers presumably initially used by house painters—the resinates or rosinates. These contained a metallic compound such as lead or manganese mixed with rosin (colophony). References to these driers did not appear in artists' manuals until after the turn of the 20th century (e.g., Church 1915, 113). According to a modern account (Elm 1934, 387):
When in 1885 the so-called soluble driers (the fused and precipitated linoleates and resinates of lead and manganese) made their appearance, the industry was very slow in accepting them. … This may have been caused partly by the difficulty of manufacturing entirely satisfactory soluble driers of this type.
3.6 PROBLEMS WITH DRIERS AND PIGMENTS AS DRIERS
Throughout the literature consulted, authors warned of problems associated with the use of driers. The darkening of pigments and media associated with lead driers and the formation of lead sulfide have been discussed above. Other problems were attributed to excess amounts of driers. As Field (1835, 56) explained, the use of too much drier “renders oil saponaceous, is inimical to drying, and injurious to the permanent texture of the work.”
Field's reference to the texture of the work being affected by an excess of drier may relate to a condition described in a modern source (Martens 1974, 404) as “seeding”:
The occurrence of an unexpected and undesirable rough-textured appearance of the coating surface after drying [seeding], is caused by an incompatibility of ordinarily soluble formulation components. This condition, although occasionally caused by a reaction of lead driers with acidulous vehicles, is more often brought about by other sources such as the presence of highly polymerized particles of vehicle or moisture contamination.2
In recognition of the dangers associated with the use of driers, Field attempted to tailor the use of drying agents more specifically to the requirements of individual pigments (table 2). There were also occasional attempts to avoid their use altogether. For example, one author recommended that artists add small amounts of fast-drying pigments to pigments that were slow drying (table 3). Artists also were advised to paint their first layer of paint (called the dead coloring) with fast-drying pigments exclusively, choosing from lists of the appropriate pigments (table 4).