White lead, or lead carbonate,1 is the pigment that formed the basis of most oil paints used in the decoration of houses until comparatively recently. When combined with linseed oil it forms a lead soap2 which gives it excellent working properties – drying and covering well it produces a slightly elastic film which enables it to expand and contract with changes in the temperature in unison with the surface to which it has been applied. The main drawback, however, is its toxicity.
Here is an early nineteenth century account of the method of making white lead:3
Sheets of lead about two feet long, five inches broad, and a quarter of an inch thick, are rolled up in loose coils, and placed in earthern(sic) pots, each capable of holding six pints of fluid, but into it as much vinegar only is poured as will rise so high as not to touch the lead, which rests on a ledge half way down. The pots are then buried in fresh stable litter, where they remain for about two months, during which time the vapours of the vinegar, elevated by the heat of the dung, oxidize the surface of the lead, and the oxide combines with the carbonic acid gas4 evolved from the fermenting materials of the bed. The carbonate appears as a white scaly brittle matter on the surface of the lead, and is separated by spreading the coils upon a perforated wooden floor, covered with water, and drawing them to and fro by rakes, which process detaches the white lead, and causes it to sink through the water and the holes of the floor to the bottom of a vessel placed below. It is afterwards ground in mills with water, and then dried in earthern pans, placed in stoves. It was formerly ground dry, by which method, from its deleterious nature, the workmen suffered severely.5
This process, known as the Dutch Stack method,6 continued unchanged, with one small exception, until the twentieth century. A patent, obtained by one Richard Fishwick, in 1787, suggested the replacement of the horse manure with spent tan-bark.7 The aim being to transmit a higher and more uniform heat to the lead and vinegar, thus ensuring a faster and more efficient conversion to white lead.
The building of the stacks, which were usually twenty-two to twenty-four feet high (6.7m – 7.3m) was carried out by women, who worked barefoot carrying the tan-bark in baskets (see below). In the United Kingdom Newcastle-upon-Tyne was one of the principal sources of production, with other centres being in London, Glasgow, Chester, Bristol and Sheffield.
The taking down of the stacks was performed by men only, who wore the regulation costume required by the Home Office for all workers in the white lead industry. The stacks were also dampened down to settle the dust. Special rules had been laid down by the 1883 Factory and Workshop Act and further regulations in 1896 prohibited women from working in contact with white lead.8 The toxic nature of the pigment had been widely known for many years. Indeed, Pliny had warned of the various ways in which the pigment could cause harm. Alternatives to lead were considered at various times9 but it was not until the twentieth century that a satisfactory option, in the form of titanium dioxide, was introduced.
The corrosion of the lead coils (buckles were frequently employed at a later period) took between three to four months. Inevitably efforts were made to speed up the process and in the late nineteenth century various modifications of the Dutch Process were introduced.
One of these was known as the Chamber Process. Here, heat and moisture, as steam, together with acetic acid and carbon dioxide were introduced into the building. The lead was hung in strips in the chamber, which was heated to a temperature of 60° C. The time taken to produce lead carbonate was reduced to about four to six weeks.
Chamber lead is somewhat different in character to stack lead, being decidedly brighter in colour, probably owing to the absence of the tan-bark, which may, to a slight extent, stain the stack lead and also cause discolouration due to by-products. It is also somewhat finer and more uniform in grain. Paint made with it works rather differently under the brush from that prepared by stack lead owing to the difference in texture, being smoother and having greater spreading power. For the same reason the oil absorption of chamber lead is distinctly higher than that of stack.8 In more recent times even quicker methods of production have been introduced and the Precipitation method can now produce white lead in a matter of minutes. Needless to say, any paint made with modern lead will produce a very different effect to paint made from Dutch Stack lead. The implications of this will be touched upon in a later essay on Lead Paint.
As has been suggested by the requirement to dampen down the stack before taking it down, white lead in powder form is considered especially dangerous. One method of reducing the risk to those who handled the pigment was to buy it ready-ground in oil, as a thick paste, rather than as a powder, and it was available in this form from a very early date. Although several authors mention the casks of ground white lead kept ready for sale at the colourman’s, others point out the need to obtain the pigment in dry cakes to ensure that it was free from adulteration. Indeed, it would appear that there was as much concern about the pigment being pure, as there was about the “deleterious” effects of using white lead. A number of the later published works gave quite sophisticated tests for the detection of adulterants.
The above watercolour shows a painter and his apprentice leaving Mr Allen’s, the Colourman, in St. Martin’s Lane. The small wooden cask on his shoulder may well be 28lb (12.7kg) of white lead paste.
This was caused by continual absorption of lead into the system over a long period – either by the inhalation of dust or spray or by ingestion through the mouth. The symptons are weakness, constipation or diarrhoea and severe abdominal pain (known as Painter’s Colic) followed by nausea and anaemia. In its more advanced stages it may cause paralysis. One of the features of lead poisoning is the gradual weakening of the muscles which led to the condition known among painters as “drop-wrist”.
An early house-painter would very rarely keep a pet dog as the sweet taste of lead dust on his overalls was something that few animals could resist with fatal consequences.
1 Also known under various other names – Lead White; Ceruse; Flake White and Nottingham White being a few. When one gets into the field of artists’ pigments there were a bewildering variety of types and names used – Body White; Crems or Cremnitz White and Vienna White being but a few.
2 Lead soaps are “organic compounds which are formed by the interaction of lead pigments and driers with the fatty acids of the drying oils used in paint. When viewed through a microscope the lead soap is seen to radiate outwards from the particles in a fibre-like manner. In a heavily pigmented paint the particles are so close together that the fibres intertwine, an action which reinforces the film and imparts great toughness and elasticity. The formation of lead soaps is one of the specially desirable features of a lead paint, producing a waterproof film which expands and contracts in conformity with the surface to which it is applied giving a tough, durable, protective coating.” J.H. Goodier. Dictionary of Painting and Decorating. 3rd edn. 1987. s.v. “Lead Soaps”.
3 It is interesting to compare this account with one from the early eighteenth century.
4 Carbon dioxide
5 P.F. Tingry. Painter’s and Colourman’s Complete Guide. 1830. p.51.
6 The Dutch had long been credited with the invention of this process; however, as Clifford Holley pointed out in his The Lead and Zinc Pigments of 1909, the Venetians were probably responsible for developing a system introduced even earlier (ibid, 8). John Smith alluded to this in the second edition of his The Art of Painting in Oyl of 1687 (ibid>, 14), while the Frenchman Jean Felix Watin also acknowledged the quality of the Venetian product, but regarded the Dutch and English as having monopolised the industry of late (L’Art du peintre, doreur et vernisseur 1778, 19).
7 The crushed bark of the oak or other trees, an infusion of which is used in converting hides into leather. SOED 1986. s.v. “Tan bark.”
8 However, even in a book of 1893 one reads of the “happy-go-lucky” philosophy of white lead making (George Terry. Pigments, Paint and Painting. 1893, 192). One also reads that many of the Regulations were being ignored and that women were still carrying out work that involved contact with white lead.
9 In 1782 Guyton de Morveau had published a paper that examined all the white materials that might serve as an alternative white pigment.
10 Noel Heaton. Outlines of Paint Technology. 1928. p.61.
11 White lead is a heavy pigment, having a molar mass of 267 g/mol compared to chalk, which has a molar mass of 100 g/mol.
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