Lead white is the most important white pigment used in painting throughout history. It was known to the ancient Egyptians, Greeks and Romans and commonly used in the preparation of ointments and plasters, as well as cosmetics. It was first identified in literature as a pigment by Pliny, who mentions it, among other colors, as used by the ancients to paint ships.
Although Davy failed to find lead white in his examination of the pigments discovered in the excavations at Pompeii, he believed that it was commonly used, and that the ancient Romans prepared lead pigments of different hues between Pliny’s usta or minium and partially calcined lead white or massicot. The ancient Romans attained considerable skill in the preparation of pigments and the manufacture and sale of colors was a well-established branch of industry and commerce in the Roman empire. One of the shops discovered in the excavations at Pompeii had jars of pigments displayed in long rows ready for sale to the artist and painter.
Lead white is lead carbonate hydroxide (basic lead carbonate) with the chemical formula of 2PbCO3,Pb(OH)2. It has been made since antiquity using variations of the process known as the ‘stack’ or ‘Dutch’ process whereby lead is exposed to acetic acid vapors in the presence of moisture and carbon dioxide; the latter is generally provided by fermenting matter (horse manure, waste grape skins, tan bark), which also provides a constant source of heat. In this process, the air supplies the oxygen, while the fermenting matter gives off carbon dioxide and moisture. The acetic acid, in the form of vinegar, converts the lead, forming basic or tribasic lead acetate, which is afterwards decomposed by the carbon dioxide to form basic lead carbonate.
History of Lead White Manufacture until the Twelfth Century
The method of preparing lead white pigment, which were common in Europe until the twelfth century, were probably the same as those used by ancient Grecian and Roman painters. Pliny mentions the use of a native ceruse (Middle English, from Middle French céruse, from Latin cerussa) found on the lands of Theodotus at Smyrna. “At the present day,” he continues, “all ceruse is prepared from lead and vinegar.” The native ceruse, suggests Ajasson one of Pliny’s commentators, was native lead carbonate or cerussite. Ceruse, lead white, is prepared in much the same manner as described by Pliny as it was throughout history until the beginning of the twentieth century. Pliny provides the following detailed account of its preparation:
“It is made from very fine shavings of lead, placed over a vessel filled with the strongest vinegar; by which means the shavings become dissolved. That which falls into the vinegar is first dried, and then pounded and sifted, after which it is again mixed with vinegar, and is then divided into tablets and dried in the sun, during summer. It is also made in another way: the lead is thrown into jars filled with vinegar, which are kept closed for ten days; the sort of mould that forms upon the surface is then scraped off, and the lead is again put into the vinegar, until the whole of the metal is consumed. The part that has been scraped off is triturated and sifted…”
One of the few surviving, early medieval, Latin treatises, De coloribus et artibus Romanorum, attributed to Eraclius, written at some time between the seventh and twelfth centuries, constitutes three books about Roman techniques of the applied and fine arts. Eraclius describes many subjects, such as how to prepare drying oils, make lead white, prepare wood for painting, etc. He says: “If you wish to make the white which is called ceruse, take lead plates and put them into a new jar, and so fill the jar with very strong vinegar and cover it up, and set it in some warm place, and leave it so for a month; then open the jar and put what you find adhering to the strips of lead into another jar, and place it upon the fire, and keep stirring up the color until it becomes as white as snow.” This description is similar to those given by Theophrastus, Vitruvius, Pliny and Dioscorides, but would seem to result in lead acetate and not lead white or at least a mixture of the two substances. It is interesting to note that Eraclius in another place recommends the use of decomposing dung to furnish heat. He describes a process for making a green pigment as follows: “Mix vinegar with strong honey, and then cover up the vase itself in very hot dung, and so take it out after twelve days have elapsed.” This recipe occurs in the first book of Eraclius, which is acknowledged to be the earliest portion of the manuscript, and is thought by many authorities to have been written before the tenth century.
In the tenth century, the author of the Mappae Clavicula describes the process of making lead white as follows: “Cast lead into plates or sheets, then suspend over strong vinegar. After it is corroded scrape it off and wash well.” Another method proposed directs that lead cast in plates be placed in a new pot partly filled with vinegar, the pot is then covered closely and put in a warm place, and left undisturbed for a month. Upon opening the pot the corroded lead should be removed and thoroughly washed, “when it will become as white as snow.”
Theophilus, a monk living in the twelfth century, gave instructions on how to make lead white: “If you are going to make ceruse, thin out some lead plates and lay them together, dry, in a wooden chest in the same way as the copper above. Then pour hot vinegar or urine to cover them. After a month pry off the lid and remove whatever white there is and replace [the plates] as before.”
After describing the method in which the lead plates should be prepared and placed in the wooden chest, Theophilus refers to the preceding recipes for directions for further treatment. In the recipe for making “salt-green,” which is a pigment prepared from copper plates, Theophilus gives essential directions for preparing the wooden chest: “Get some thin twigs and place them in the above-mentioned chest in such a way that two-thirds of the cavity are beneath [the twigs] and the other third is above them. Then lay them [the plates] next to each on the twigs and cover them carefully with another piece of wood, fitted for this purpose, so that no vapors can escape. Next, in the corner of this piece of wood drill a hole through which you can pour heated vinegar or hot urine until a third of [the chest] is filled; then block up the hole. Put this chest in a place where you can pile dung all over it.” It appears therefore that the direction to bury the chest in dung is omitted simply to save a tedious repetition. Assuming this idea, we have in this description the recommendation of the use of manure as a source of heat, and possibly a source of carbon dioxide necessary for the production of lead white. There can be no question of the use of dung for similar purposes to make green copper pigments, as both Eraclius and Theophilus recommend it.
Centuries later, Didron found in a convent at Mount Athos, in Greece, a manuscript, portions of which the monks claimed to be unquestionably of Byzantine origin, and copied as early as the tenth or the eleventh century. The manuscript received additions from time to time and copies were frequently made from it for distribution. The following directions are found in this manuscript under the title, “How to Make Ceruse: Take lead cut into thin pieces, and suspend these pieces in a pot filled with vinegar; close tightly this pot, and bury it in fresh dung in a warm place. At the end of ten or fifteen days take up the pot and throw the lead upon a stone and grind it; put the product in a large vase and dry it, and you will have a good ceruse.”
The descriptions of the methods used to make lead white in these manuscripts form a link between the methods described by the Roman and Greek authors and those in practice until the twelfth century. While in general they resemble the methods recommended by Theophrastus, Vitruvius, and Pliny, inferring that the differences are only such as would naturally occur in their transmission by copying through ten centuries, yet Theophilus and Eraclius both imply that dung was used as a means of producing the necessary heat. The absence of any clue to provisions for supplying carbon dioxide required to produce lead white can be disregarded, because the vinegar used in those times was probably largely contaminated with substances that produce by their decomposition carbon dioxide in sufficient quantities. There can be no doubt respecting the product of the methods described by Theophilus and Eraclius.
Lead White Manufacturing from the Thirteenth to the Nineteenth Centuries
Among the manuscripts collected by Jehan Le Begue is one by Petrus de Sancto Audemaro, who lived in the north of France, late in the thirteenth or early in the fourteenth century. Some of the formula of this author are considered to be much older than his time, among which is the following: “White and green colors, without salt, are made and tempered as follows: pour strong vinegar into a vase and place twigs across it inside the vase, and then place strips of lead, and other strips of copper or brass, suspended in the air by means of twigs, so as not to touch the vinegar or each other; then close the vase very carefully and lute it with clay or cement or wax, so that there may not be the least hole through which the vinegar may exhale. Then cover it with horse-dung, and after thirty days, on account of the acidity of the vinegar or wine (for the wine, on account of the heat of the dung, will become vinegar), the copper or brass will be found to be turned green, and the lead white. Take the lead white, dry it, grind it, temper it with wine to paint on parchment, and mix it with oil to paint on wood.” The vinegar recommended here is probably a mixture of wine lees (deposits of residual yeast and other substances that settle to the bottom of a vat of wine after fermentation) and wine or vinegar in which fermentation had begun but was incomplete, because as Audemaro says, “The wine, on account of the heat of the dung, will become vinegar.” Audemaro also instructs that the pots containing the lead and vinegar be buried in beds of dung; and in describing the manufacture of salt-green, he recommends that the operation be conducted in a horse stable. This author also suggests that grape pomace (the solid remains of grapes after pressing for juice, containing the skins, pulp, seeds and stems of the grape) be used as a source of fermentation instead of horse manure, saying it will produce the same result.
A manuscript preserved in the library of the convent of Saint Salvatore, in Bologna, and entitled Segretti per Colori is a collection of recipes for making and preparing colors for painting, dyeing, etc. The name of the author is unknown, but the date of the manuscript is considered to be about the middle of the fifteenth century. The compiler describes the manufacture of lead white as follows: “Take leaden plates, and suspend them over the vapor of vinegar in a vase, which, after being luted, must be placed in dung for two months; then scrape away the matter that you will find upon the plates, which is the lead white. Do this until the plates are consumed.” The author of this treatise adds the following instructions for purifying lead white: “Take ceruse, put it in a clean jar, which should be placed over the fire, stir the ceruse continually with a stick, and it will become white.”
Pierre Le Brun now in the Public Library at Brussels, wrote a painter who probably resided at Paris a manuscript, in 1635. Le Brun says that lead white is made “by putting vine branches in pots, pouring vinegar over them, fixing sheets of lead on the top, and fastening them up air-tight.” He mentions, in a list of white pigments, ceruse, blanc de Venise, and blanc de plomb, as if they were different substances. Writers of his time generally refer to Venice lead white as being the best, and it is probable that lead white, which was then manufactured in Holland and perhaps in England, was adulterated and given different names, each indicating a certain degree of impurity.
The manufacture of lead white is described in a large number of sixteenth and early seventeenth century manuscripts, the earliest of which, MS. Sloane 122, includes a detailed explanation of the way in which a barrel should be prepared with two gallons of vinegar at the bottom and strips of lead suspended inside above the vinegar. After the barrel has been made as air-tight as possible it should be left for eight weeks, when it can be opened up and the white pigment knocked off the lead strips. In discussing the methods of lead white in medieval times, Thompson points out that this class of medieval recipe for making lead white is different from the type that closely resembles the stack process. In this class, the lead is hung over vinegar in a pot, and the pot is then sealed up tightly and buried in hot dung. If the pot is sealed it is hard to understand how the carbon dioxide can reach the lead and cause the reaction resulting in lead carbonate. Presumably, these methods only make lead acetate, which is the same objection to the methods described by writers, such as Pliny, before the twelfth century.
It is possible that this was actually the case; lead acetate was formed in these methods and not lead white, because the product of these recipes was regularly subjected to a special after-treatment not specified for lead white made by other methods. It was roasted gently in the open air. It is possible this roasting might, under some conditions, produce lead carbonate from the acetate. If this explanation is accepted, then we come to realize that there were two types of lead white in use since antiquity through medieval times: one much the same as stack process lead white, and another somewhat different. The differences may not have been that noticeable.