The Materials and Techniques of Medieval Painting

Daniel V. Thompson

• Publisher: Dover Publications
• Year: 2012
• ISBN:
  9780486142036
• Topic: Art
• Subtopic: Techniques d'art

Medieval painters built up a tremendous range of technical resources for obtaining brilliance and permanence. In this volume, an internationally known authority on medieval paint technology describes these often jealously guarded recipes, lists of materials, and processes.

Based upon years of study of medieval manuscripts and enlarged by laboratory analysis of medieval paintings, this book discusses carriers and grounds, binding media, pigments, coloring materials, and metals used in painting.
It describes the surfaces that the medieval artist painted upon, detailing their preparation. It analyzes binding media, discussing relative merits of glair versus gums, oil glazes, and other matters. It tells how the masters obtained their colors, how they processed them, and how they applied them. It tells how metals were prepared for use in painting, how gold powders and leaf were laid on, and dozens of other techniques.
Simply written, easy to read, this book will be invaluable to art historians, students of medieval painting and civilization, and historians of culture. Although it contains few fully developed recipes, it will interest any practicing artist with its discussion of methods of brightening colors and assuring permanence.
`A rich feast,` The Times (London). `Enables the connoisseur, artist, and collector to obtain the distilled essence of Thompson's researches in an easily read and simple form,` Nature (London). `A mine of technical information for the artist,` Saturday Review of Literature.

CHAPTER I

CARRIERS AND GROUNDS

TECHNIQUE in painting is the sum-total of all the methods by which coloured bodies are fastened upon supporting grounds according to the wish and plan of the painter. In this volume we shall examine some of the grounds, some of the coloured bodies, fastening agents, binding media, and, incidentally, some of the methods, which make up the dominant painting techniques of Europe in the Middle Ages.

Terminology

The word “ground” in connection with paintings is a little ambiguous. If a picture is painted on a brick wall covered with plaster, either the brick or the plaster might be called the ground. By common consent, however, nowadays, the plaster in this case is usually called the ground, and the brick wall the “carrier.” So in a panel painting the wooden panel is called the carrier, and the layer of gesso, or plaster, or whatever there may be between the wood and the painting, is called the ground. (Grounds on canvas are still usually called “primings.”) Sometimes there is no distinction. Sometimes the carrier itself is also the ground, most obviously so in writings or drawings or paintings on paper or parchment.

The Importance of Book Painting

It is a quaint custom of our time to class the productions of artists which touched the lives of other ages most closely as Minor Arts, among them (along with the vase paintings of Greece, the carpets of Persia, and the ceramics of the Far East) the book paintings of medieval Europe. Let us not be deceived by the phrase. More compositions were planned and executed by illuminators than by any other class of medieval painter. The writing and illuminating of books were the major preoccupation of many artists, and constituted in some respects the greatest of all the medieval arts. It is not easy for us to see the book paintings of the Middle Ages with medieval eyes ; for the pictures and the writings were generally meant to be read together. Books were made to be read, and illumination was built in, with all the forces of Ingenium, Intellectus, and Ratio, not sprinkled on the top like candied violets or hundreds-and-thousands on a dish of trifle.

More medieval paintings were done on parchment than on any other material; for most medieval books of any pretension were written on parchment. Parchment provided an agreeable, beautiful, and durable ground not only for the writing but also for painting and gilding.

Parchment-making

Parchments in the Middle Ages were a standard article of commerce, prepared by specialists ; and the men who used them did not necessarily know very much about how they were made. We share their ignorance. We tend to take the parchment of medieval books for granted. We know, of course, that parchment was made from the skins of animals, with the hair removed. We know that the skins were usually soaked in water to clean them up, and then in a broth of lime and water to loosen the hair. After a skin had been limed for a few days, the wool or hair could be pulled off or rubbed away quite easily, and some of the fat and oil in the skin was washed out by the lime. The skins were rinsed thoroughly in fresh water, and stretched on frames to dry.

According to a Latin text written in Germany in the thirteenth century, the parchment-makers of Bologna, who were famous for their products, used to lime their skins twice, once before and once after “pulling” ; and then to wash them very thoroughly, and leave them for two days in fresh water before stretching them on hoops to dry. Nowadays, instead of hoops, rectangular frames are used. An edge of the floppy wet skin is caught over a little button and tied around with a cord. This cord is run over to a peg in the rectangular frame, and when the skin is loosely supported on all sides by cords in this way the pegs are turned around until the cords are tightened and the skin stretched evenly. Parchment shrinks a great deal in drying, and if it were tacked on frames, it would tear itself away from the tacks. When it is dry, if it has been properly stretched, the skins is as taut as a drumhead.

In modern parchment-making the skins are allowed to dry on the frames and then scraped smooth. It is not necessary to do very much scraping, because in a modern factory the wet skins will previously have been “split” to an even thickness all over by being drawn against an oscillating knife. But in medieval times the skins were scraped on the frames while they were still wet. The wet skin was soft and pliable, and if the workman pressed a knife against it, it would give. If the knife had a straight edge and sharp corners, the corners would cut through ; if the corners were rounded off, the ends of the knife would still press harder against the flexible skin than the middle of the blade. The only way to get an even pressure all along the blade was to make it moon-shaped. Paul of Prague, in the fifteenth century, gives us a list of tools in which the parchment-maker’s knife is called a lunellarium. This must certainly have been moon-shaped. Even now, for dry scraping, a round-bladed knife is used. It has to have a special kind of edge, a “burr,” made by turning over a hair’s breadth of steel at the edge of the sharpened blade, just as cobblers’ and leatherworkers’ knives are burred.

Scraping with the knife made the skin thin and even. It was left on the stretcher until almost dry, and the flesh side was then rubbed with pumice to make it perfectly smooth. It was remoistened and rubbed with pumice several times, and finally stretched tight and allowed to dry completely.

When a skin was very fat and oily, it was necessary to draw the oil with alkalis ; and ashes, or ashes and lime together, were used for this purpose. They were made into a paste with water, and smeared over the skin while it was still wet on the stretcher. Sometimes the skins were treated with alum, as we learn from fifteenth-century English texts ; and that must have had the effect of hardening the parchment, and making it more like leather. Some medieval parchments have this quality of hardness, and perhaps it was produced in this way.

Vellum

We know that calf skin was sometimes used for making the pergamenum vitulinum, that is, the “veal parchment” which we call vellum. It was necessary, of course, to have a large skin to begin with if a large piece of parchment was required. The huge late medieval choir-books had to be done on vellum; for a sheep or goat skin would not have yielded a double folio of such size, and single pages could not be bound satisfactorily. A curious tendency has become established in modern times to think of the word vellum as somehow more elegant and complimentary than the word parchment. Etymologically, “vellum” means calf skin and nothing else, while parchment is a general term applicable to any kind of skin, including vellum; but such is the force of refinement that the smaller and thinner a skin is, and the less the likelihood that it should be calf skin, the more likely we are to call it vellum, out of politeness.

The Latin word abortivum occasionally applied to fine parchment in the Middle Ages (though rarely) has given rise to another form of superstition which has become widespread, namely, that the finest medieval parchment, and particularly the very thin, flexible, opaque, small, thirteenth-century French Bible vellum was made from the skins of still-born calves. There is as nearly as possible no evidence for this belief. It may be true. I have no figures on infant mortality among livestock in the Middle Ages; but I should be inclined to think that animal husbandry must have been in a very precarious condition if enough calves were still-born in the thirteenth century to provide all the pages which pass for “uterine vellum.”

Qualities of Parchment

As far as we know, the vast majority of medieval parchments were made from the skins of calves, sheep, and goats, duly slaughtered. It is essential for good parchment-making that the skins be put to soak while they are still quite fresh, soon after the animals are killed. Parchment-makers must have had regular channels of supply. They could not safely have depended on picking up a skin here and there from anyone who happened to have killed an animal for meat. Probably the meat markets and the parchment-makers were supplied through the same mechanism of distribution. Probably any city’s preferences in the matter of meat diet were reflected in the local parchment industry. This is no doubt why Bologna parchment tended to be made from goat skins, while Paris parchment tended to be made from sheep skins and calf skins. It is quite possible that the skins of the deer and other game that people ate were made into parchments, too ; and it would not be altogether surprising if it turned out, as a result of experiments now in progress, that some of what now masquerades as “uterine vellum” was actually rabbit or squirrel parchment.

If the skins from which parchment is made are not quite fresh, they give a spotty product. An eleventh-century manuscript in Berne describes the sheep and calf parchments of Flanders and Normandy as “all white and smooth and handsome,” and the sheep parchment of Burgundy as “rough and mottled and thin and very ugly and uneven in colour, grey and black and white.” That may have been caused by some defect in the sheep. Fat sheep make good mutton but poor parchment, and the pasturage of Burgundy may have been too rich for the sheep to grow the sort of skins that make the best parchments. But the bad qualities ascribed to the Burgundian product sound like those caused by carelessness in the matter of getting the skins to the parchment-maker promptly.

Preparations

Parchment is sometimes ready for use as soon as it has been trimmed or cut to size. Quite often, however, the surface is a little greasy, or horny, or absorbent, and it needs to be rubbed over with powdered pumice, chalk, rosin, or colophony to make it take the ink and colours nicely. This operation is called pouncing. Natural pumice was an imported product in England, and English workers often used instead a material which is described as “better than twenty other pumices”: a sort of bread largely composed of powdered glass. Powdered glass and flour and brewers’ yeast were mixed and allowed to rise like bread, made into loaves, and baked in the oven.

Sometimes, when the illuminator wanted to be quite sure that his colours and gold would not run any danger of flaking off the skin (as they might if the skin were unduly hard and smooth), a little thin glue was rubbed over the parts which were to be gilded or painted. Parchment was sometimes stretched and given eight or ten coats of thin white lead oil paint, and then cut up and made into blocks. These little tablets were used by merchants in Italy and in Germany for calculating sums, and they were also used for drawing; but few if any drawings on this sort of material have survived. For the most sumptuous manuscripts, parchment was dyed purple with the shellfish dye, whelk red, the classic purple; and sometimes, in imitation of that, with other materials. And for a different kind of splendour of the same general sort, skins were sometimes dyed green with verdigris. Gilding on these coloured parchments is incomparably more effective than on white, and it is with gilding that they were generally used. For drawing, parchment and rag paper as well were often coloured green or pink or grey or buff with several coats of pigment mixed with thin size. Sometimes, in the fifteenth century, quite strong or dark colours were put on as grounds. Leonardo da Vinci sometimes used what seems to be pure vermilion, and Dürer, a dark greenish blue. Drawings done on these tinted papers with washes of ink and lighter values applied with white are often really paintings, and belong properly in any discussion of medieval painting techniques.

Wooden Surfaces

After parchment the most important carriers for medieval paintings are walls and wood. The reasons for the widespread use of wood are first, that it is comparatively easy to make things out of wood, and second, that things made out of wood generally call for a decorative finish of some sort. It is quite a simple matter to make a flat wooden surface, suitable for painting; and indeed flat surfaces naturally develop in the construction of almost any sort of woodwork, in doors and screens and chests, which invite people to do something in the way of embellishment. By nailing and gluing pieces of wood together, and cutting and carving them, almost any sort of shape can be made quite easily; and mouldings and ornaments can be devised in wood which it would be laborious or impossible to execute in stone or metal.

For large flat surfaces, of course, gluing up was necessary; and the Middle Ages, fortunately for themselves and for us, knew the very best material to use: a sort of cement, half like a glue and half like a cement, made out of lime and cheese. If a bit of rather poor, lean cheese is soaked in water, and crumbled up and ground with lime and a little water, it makes a sticky, treacly mixture which dries as hard as stone and which, when it is once dry, is not affected by moisture. (Very much the same sort of glue is used now for putting together the wooden parts of aeroplanes.) Among the many troubles which beset medieval paintings in our time, one of the rarest is for the glued joints of the wood to separate; and their strength is largely due to the use of this strange, homely adhesive.

The Functions of Gesso

The untreated surface of wood is not ideal for any kind of painting, except perhaps plain housepainting. It cannot always be made perfectly smooth and even, and different parts of the grain take the paint differently. In carving, too, the grain presents some difficulties. To finish a carved moulding highly in the wood means a great deal of labour, and even when it is done it is not ready to be gilded. The wooden surface is neither hard enough nor smooth enough for gilding. So it was usual to prepare the object, whether it was to be plane or carved, roughly in some fairly soft wood, and then to make the final surface on it in gesso. Gesso has no grain to make the carving difficult. On flat surfaces it can be made smooth and even without trouble. All parts of a gessoed surface are equally absorbent. And it is a perfect ground, firm, even, and resilient, for any sort of gilding.

The Use of Gesso

Gesso is simply a kind of thick white water paint, with chalk or gypsum or plaster, or something of that sort, as the pigment, and glue or gelatine as the binding medium. It is put on fairly thickly, in several coats, so that the surface, when it is dry, can be worked and carved and modelled, as much as the case requires. To make the gesso mixture adhere securely to the wooden carrier, a coat or two of glue is usually put on first. The glue sticks to the wood, and the gesso sticks to the glue. Sometimes medieval panel-makers put the glue on the panel, and then glued on strips of linen or pieces of parchment (sometimes, alas! illuminated parchment), so that if the panel cracked, or any joints came apart, the linen or parchment would still hold the gesso ground together.

Mixing good gesso is an art which the Middle Ages developed to a high degree, especially in Italy. It calls for knowledge and experience as well as the right materials. The finest, sleekest gesso is called in Italian gesso sottile, which means “thin gesso.” It has the great advantage for certain purposes of shrinking down so much in drying that it hardly obscures the form to which it is applied. That quality is not important on a flat surface; but it is very important indeed on a carved moulding. If a gesso mixture is made with chalk (as it very often was, and usually is nowadays) one or two coats of it will be enough to fill up the hollows of a finely wrought moulding or carving, and spoil the shape entirely; so a “thick gesso” of this sort has to be smoothed up with templets as it is put on, or carved away after it is dry. Even six or eight coats of gesso sottile, on the other hand, may be put on a finely carved surface without hiding the carving. This means, of course, that there is no use putting it on unless the surface underneath is nearly finished ; for if it will not conceal qualities, neither will it hide defects. On a rough, flat panel, or on a roughly carved moulding, gesso sottile would not have enough body to make the surface smooth. So the forms were evened up to begin with with another kind of gesso, called in Italian, gesso grosso, “thick gesso.” When the surfaces had been made almost perfect in this material, they were coated with the thin gesso, gesso sottile, which finished them nicely.

The Construction of a Polyptych

Suppose a Gothic painter in Italy wanted to make a great polyptych, with panels set in carved frames, with foliage ornaments and mouldings and crockets and all the trimmings. He would glue up his panels first with cheese glue, and build the skeleton of the framework. He would do all the carvings (or, more likely, have them done), some of them in place, and others to be glued or pegged or nailed where they were to go. He would run his mouldings with planes and chisels and gouges, and carve out roughly any little water-leaf or egg-and-dart or other embellishments that his design called for. He would fix up little niches, perhaps, with carved figures in them, or turn any freestanding columns, or cut in any little rose windows or ornaments of that sort in the wood, without taking any particular pains to finish them up in detail. Then he would assemble the whole thing. He would glue it up with cheese-lime glue; and where he put in nails, he would cover their heads with bits of tinfoil glued over them, so that no rust should come through to stain his gesso. He would brush a a coat or two of thin hot size or glue over all the woodwork; and follow that, after a day or two, with a stronger coating of the same material. When that was dry, he might glue bits of linen all over the flat panels, to strengthen them in case of cracks.

Then he would make up a great kettleful of size, by boiling bits of skin or parchment in water, and prepare his gesso grosso, the thick foundation gesso, by grinding plaster of Paris with this size. He would apply several coats of this gesso mixture all over his polyptych with a brush; and on the flat surfaces he would put it on with a spatula, to get it thick and even.

When mixed with size, plaster of Paris dries slowly, but it dries extremely hard. When it was thoroughly dry and hard, the workman would go all over the surface, shaping every...