MATERIALS & METHODS
Thompson, Daniel V., Jr., Research and Technical Adviser, The Courtauld Institute of Art, University of London. The Practice of Tempera Painting. New Haven: Yale University Press. 1936. Fourth Printing, 1946.
Metals in the Design
These metals, gold and palladium, may be applied to a gessoed panel in such a way as to make the panel seem a solid block of shining metal. In spite of their brightness, however, fields of burnished metal must be treated as darks in the design. Only when their reflecting power is increased and broken up by graining the surface may they be thought of as lights in calculating their effect. Areas of metal and color may be so arranged as to suggest that the painting has been executed upon massive gold, or inlaid in it, or enameled in the surface. Some early Italian paintings on gold grounds suggest quite strongly that their authors wanted to capture the effect of enameling in massive gold. The purist may resent this sort of deception. If so, he should avoid the use of burnished metal grounds altogether; for they necessarily produce the look of solid metal. The happiest results of burnished metals in painting design come from accepting the convention that the metal is solid, and that [p. 51] it shows where solid metal might--either as a ground under the painting, seen wherever the color stops, or as a pattern of insets into the ground, or of metallic incrustations upon the ground. The conventional acceptance of gilding for solid gold is so old and so well established that it is hardly open to criticism. We are quite satisfied that picture frames should be gilded: we do not require that this innocent deception be abandoned, and the frames be made of solid gold. Many people do no want frames to look like gold at all; but that is another story. [pp. 51-52]
Bole for Gilding
If you want any areas of burnished gold [or palladium] on your panel, this is the way to apply them. Get some "Armenian bole" and grind it fine with water. Or buy some red burnish gold size already ground in water from a dealer in gilders' supplies. The best bole is very "fat," and almost transparent, and warm, almost orange in color. It is sold in little conical lumps, and can be bought from any of the great English colormen. It can also be bought in hardware stores in Italy, and there costs practically nothing; but in America it is rather hard to find. American gilders usually use darker, more opaque bole, not far from the color of Indian red; and this kind does just as well. The only advantage of the warmer bole is that the color which shows through when any gold wears off is more agreeable. There are gray and yellow boles, too, and they are perfectly usable. "Gilder's Gray Clay," in fact, is a little easier to burnish than the red kind; but if there are any imperfections in the gilding, it is an ugly color that shows through. With a good red bole, slight faults are tolerable, and the effects of age and wear are often considered a positive improvement.
If you buy the bole, or gilder's clay, in the form of a paste, keep it covered all the time. If you grind the bole yourself, put it into a covered jar as fast as you grind it; for dust and lint in the bole will injure the gilding . [p. 52]
Mixing and Applying the Bole
Dissolve half an ounce of gelatine in ten ounces of water, and put a little of the solution into a clean cup. Add a little of the ground bole to it, and stir it thoroughly with a well-washed brush. The proportions of size and bole are not important. You simply want a coat of size with some color in it. A teaspoonful of bole and four or five teaspoonfuls of size is a safe rule; but the amount of bole in a teaspoonful depends so much on how wet the paste is that the rule does not mean very much.
Make quite sure that your panel is all smooth and free from dust. It is a good plan to wipe it over with a piece of slightly damp cheesecloth. Then put a coat of the thin bole mixture over all the parts which you intend to gild, lapping a little bit over the outlines which you have scratched into the gesso. You always have to gild over these outlines: it is not safe to try to gild right up to them. The best brush for putting on the bole is a red sable water-color brush. It need not be very large, even for large areas of gilding, but it must be large enough to hold a fair amount of the liquid. Apply the mixture as evenly as you can, and take pains to avoid leaving drops and trickles behind. The brush should not be too full. Wipe it off on the back of your left hand [not on a cloth] before you begin. And above all, do not try to move the bole around on the gesso after you have laid it. Put it on, and leave it. Even if there are imperfections, do not try to improve them while they are wet, or you will make them worse. If you miss any little parts, touch them in after the surrounding parts are dry, and not before. Let this first coat dry entirely, as it will do quite quickly.
Throw away the thimble mixture, and wash out the brush. One reason for putting on this first thin bole is to wash the surface of the gesso where the bole is to come, and you may assume that the brush has carried bits of dust back into the liquid. Put some more of the ground bole into the cup, and add enough of the gelatine solution to make a rather thick cream. It should not be a paste, but a thick, creamy liquid, which will drop from the brush in large drops. It is better to have it too thin than too thick, and the exact proportion does not really matter; but a rich mixture goes on more smoothly. [p. 53] The size should be liquid when you mix it up. If it has set, warm it a little. The mixed bole, too, should be warmed a little if it shows signs of setting to a jelly. It is a good plan to strain this bole mixture through a piece of chiffon before using it; and the cup with the brush in it should be kept covered with a cap of paper all the time, except when you are actually putting on the bole. You can not be too careful about dust, if you want to do perfect gilding. [pp. 53-54]
How Much to Put On
Apply at least four coats of this bole allowing it to dry out entirely between coats. On flat surfaces, it is best to use many thin coats as many as six or eight; but on moldings the smoothest work is done by floating the bole on rather generously with a fairly full brush. The whole thing boils down to getting a good coating of bole on as smoothly as possible; and each workman will find his own best way of doing it, for his particular job. If you are working with an opaque bole, you may lay enough coats to produce a solid, uniform color over the areas to be gilded. If your bole is transparent, the color is not such a useful guide. In either case four coats will probably be enough, unless they are extraordinarily thin. And if you want to be quite sure, you may put on a few more; for if you lay them evenly, they will do no harm, in any case. [p. 54]
Polishing the Bole
When the last coat of bole is dry, the panel may be gilded. But it saves some trouble in burnishing if you polish the bole, and put on one more coat. To polish it, you may use the very finest emery paper, or better, fine sandpaper, as follows. Take a sheet of the finest sandpaper, and spilt it. That is, strip as much of the paper off the back as you can, to make it thinner and more flexible. Then take two bits of it and rub the sanded surfaces together to wear away as much of their cutting power as possible. The result will be a very fine soft sandpaper with which you may rub over the bole surface safely. It will grind off any little unevenness, but will not cut through, and it will polish the surface of the bole so nicely that the burnishing later on will go more easily. After this sandpapering, you must dust off the panel thoroughly with a linen cloth, and apply one last coat of bole. Unless you are going to gild immediately, cover the panel with a cloth, to protect it from dust.
When you are ready to begin gilding, take a piece of soft old linen and rub over the bole quite hard, to polish it a little. You may burnish it before gilding, and it is an excellent thing to do so; but rubbing directly on the bole spoils the surface of a burnisher fairly quickly, so a special burnisher should be kept for this purpose if you wish to make a practice of it. [pp. 54-55]
Gilding with Glair
In place of size as a medium for applying the bole, glair may be used, as Cennino describes. It is equally good, but I think no better; and requires a little more care in wetting down for the gilding, as the glair is apt to dissolve in the water and the bole to come off on the brush. Cennino's directions may be followed exactly, without difficulty, provided one realizes that the drinking glass he speaks of is not an eight ounce tumbler but more like a two-ounce sherry glass. Beat an egg white to a stiff foam, and pour two ounces of cold water on it. Let it stand over night, and pour off the liquid. Grind some powdered bole with this liquid glair to a stiffish paste. Mix a little of this paste with a good deal of the glair, say one teaspoonful of the ground bole to five of glair for the first coat. For each successive coat, add more of the paste of bole to the glair mixture, and put on at least four coats. The last coat will, of course, be quite thick with bole. In laying the gold, use water without alcohol, but put in a little old glair. The older the glair is, within reason, the stickier it is, and the better for gilding. It is possible to build up a tolerance of the smell of stale glair; but most people will be happier gilding with size. [p. 55]
Tools for Gilding
Gold leaf is, of course, extremely thin, and it requires three special tools to handle it easily. First, a cushion on which to cut it; second, a knife to cut it with; third, a special kind of brush, called a tip, to lift it after it has been cut. All these should be bought ready-made from a gilders' furnisher; but when this cannot be done, substitutes can be devised, as follows. [p. 56]
The gilder's Cushion
To make a cushion, take a little panel of wood, 6" x 10", or larger, and cut a sheet of absorbent cotton of the same size off a roll. Half the thickness of the usual roll of cotton is enough, but more does no harm. Lay it on the panel, smoothly, and cover it with a piece of leather, with the rough inside surface upward. Chamois skin or imitation chamois [as long as it is real skin, and not cloth] may be used instead of leather. Tack the skin around the edges of the panel, drawing it as tight as possible. This will give you a smooth, padded leather surface upon which to cut the gold. Then cut a strip of stiff, tough paper 14" x 11", and tack it around one end of the panel, so that it comes along each side for four inches, and makes a screen eleven inches high. This screen incloses a space four inches long and the width of the panel, and in this you may keep a supply of gold leaves ready to be laid out on the cushion, without much fear that they will blow away. Fold the paper screen down flat upon the leather cushion, and then fold the sides over on top of it. In this position it keeps the cushion clean when out of use. To finish it off, a strip of leather may be fastened around the edge of the panel, covering the tacks, and strips of leather tacked to the bottom of the panel forming a wide loop for the gilder's left thumb to pass through, and a flat loop for the gilder's knife. [p. 56]
The knife for handling and cutting the gold leaf should have a blade at least ten inches long. This blade must be perfectly straight from end to end, and not too flexible. A kitchen spatula can be used, but it is not likely to be satisfactory. Even an ordinary table knife can be used; but the long, straight, rather stiff blade is a distinct advantage. If a proper gilder's knife is not available, any knife can be pressed into service. It should have a smooth edge, but not sharp. If the edge is sharp, it will cut the cushion. To adapt a straight-edged carving knife or kitchen knife for use as a gilder's knife, it should be sharpened and then made dull by rounding off the edge on the stone. [p. 57]
The Gilder's Tip
The gilder's tip consists of camel's hair set thinly between cards. The width of the card is a little greater than that of a leaf of gold, and the length of the hair varies according to the size of the pieces which the gilder habitually uses. If he wants to take up whole leaves of gold at once, he needs a whole-leaf tip, with very long hairs; and if he is gilding chiefly small areas and lines, he will prefer a tip with short hairs, perhaps only an inch long, or even less. For general purposes, the beginning gilder will find a half-leaf tip, with hairs about two inches long, adequate to his needs. It is useless to try to make tips for oneself, and they are almost indispensable for good work. [p. 57]
If for any reason a tip cannot be procured, it is possible to pick up the gold on a slip of white paper, provided the paper is rubbed [p. 57] thoroughly over the gilder's face or hair and then pressed firmly on the gold; but this is only an emergency device, and should not be used regularly. Another, better method is to stretch a piece of fine silk net across the arms of a bow of tin bamboo. This will pick up the gold, and breathing on the net will release the leaf. The method that Cennino describes--sliding the gold leaf into place form a card with the corners trimmed off--is too hard to carry out with gold leaf of the modern commercial variety for many people to succeed with it. With thicker gold, it is possible; but the modern gilder will do well to use a proper tip, as Cennino would certainly have done if this ingenious simple instrument had been available in his workshop. [p. 58]
Qualities of Gold Leaf
The gold leaf used by medieval gilders was thicker than the thinnest modern gold, and probably in general a little thicker than what the modern goldbeater calls double weight. Heavy gold is a little easier to handle than the very thin leaf of trade; and it is worthwhile to buy the double weight. The cost is sometimes a little higher, as it contains more gold; but as it takes less labor to make it, some goldbeaters will supply it at about the same price as thin leaf. It is a mistake to suppose that thin leaf produces a less solid looking job of gilding. The advantage of the thicker leaf is chiefly the gilder's own convenience. He is less apt to waste gold, and imperfections in the leaf itself are less common. The ordinary gold leaf of modern trade usually contains some copper, and is often disagreeably red in consequence. Other alloys, chiefly with silver and copper are used to produce fancy shades of gold, green, lemon, and white. With all these, there is necessarily some tendency to tarnish. Pure [p. 58] twenty-four carat gold leaf is supplied on demand by all good beaters, and unless a painter has some very urgent reason for wanting something different, he will make no mistake in adopting double weight twenty-four carat leaf as the material of all his gilding. [p. 58-59]
Handling the Leaf
Handling gold leaf is an extremely simple business, but it often takes a little practice for a beginner to learn to manage the details successfully. The first principle to remember is that gold leaf will catch and stick on anything which is even slightly damp or greasy. To avoid trouble from this quarter, the cushion should be rubbed over with a little powder of dry bole [or French chalk], and the knife stopped over it thoroughly to work the powder into the leather, and to remove any trace of grease or damp from the knife. After stropping the knife on the cushion, turn the blade upright and scrape all the loose dust away lightly. Gold leaf is put up for sale in little books of thin paper, and the paper of these books is usually dusted with red clay. Nothing is better for keeping the cushion and knife in condition than to rub them with the red leaves of an old book of gold.
To put a leaf of gold on the cushion, the safest and easiest way is to open the little book of gold to the first leaf, hold it over the cushion, and let it slide off the book onto the leather, or into the paper screen. You may take the gold out of the book with the knife, but there is more risk of piercing or tearing it. It is good practice to take the gold first from one end of the book and then from the other. This usually keeps the last leaves in better condition than going straight through the book. Be very careful to keep the book of gold dry; for if you set it on a drop of water the moisture will often go right through it and make every leaf stick to the paper. [p. 59]
The use of the Knife and Cushion
When your leaf of gold has been transferred from the book to the cushion, you have to get it spread out flat on the fore part of the cushion, away from the screen, for cutting. There is only one right way to do this. Do not try to poke it into place. If the knife presses [p. 59] against the gold, it will go through it, or else press in a crease which you cannot get out. The proper motions for the knife are these. First, a little taping, flat on the cushion, to create enough of a draught to raise an edge of the leaf slightly. The point of the knife may then be passed under the gold, close against the cushion, lifting the gold slightly as it goes, until it comes out on the other side. Second, lift the gold clear of the cushion, with a little shake, to make it unfold as much as it will. Third, a slow, smooth turning, which lays the gold out again on the cushion the other side up. The edge of the leaf is brought against the cushion, its outside [as it hangs across the knife blade] against the leather, and the rest of the leaf is then unwound by the knife. This is a very simple and easy operation, and it is the whole trick in handling gold leaf. Every time the gold is picked up on the knife, it must be put down the other side up.
When you have turned the gold over in this way, you can blow some of the wrinkles out of it. If you blow straight down upon the cushion, into the middle of the gold, your breath will tend to flatten out the gold. If you blow sideways, particularly toward the edge of the leaf, you will blow the gold right off the cushion, into the air. [If you do, don't try to catch it! Let it fall where it will, and then pick it up with the knife, if by good fortune it has fallen on a dry place.] Pick the gold up on the knife again, roll it off on the [p. 61] cushion, blow into the middle of it, and repeat these operations until it lies exactly where you want it on the cushion, spread out smooth and even, without wrinkles. The most tangled leaf can be straightened out quickly and easily in this way, provided the tangles are not made permanent by pressing with the knife. Lift, turn, and blow, is the rule, and there are no exceptions. It never pays to try to push the leaf about, or to straighten out one corner by itself. Lifting, turning, and blowing all take a little practice, and a skillful gilder can unwind a shapeless little pile of gold in fewer motions than the beginner, because he knows from experience just where to lift, just where to turn the gold off the knife onto the cushion, and just how to blow the wrinkles out with a smooth, crescendo breath into the heart of the tangle.
After you have got enough practice to feel confident about handling the gold, you will spill a dozen leaves or more at one time into the screen at the back of your cushion. This saves a great deal of time, and makes the actual gilding go much more smoothly. The gilder who tries to lay his gold out on the cushion flat out of the book never learns the skill in handling leaf which this labor-saving method requires. The good gilder does not want to stop his gilding to take gold out of the book any oftener than he has to, and a dozen leaves, or two or three dozen, are perfectly safe on the back of his cushion.
When a leaf has been laid out neatly on the fore part of the cushion, and blown down firmly with a breath, it may be cut into two pieces, or any greater number, with the knife. Lay the knife straight across the leaf where you want to make the cut. Sight it, and bring the edge of the blade down firmly on the leaf. With very light pressure on the blade, push it a little away from you, and then draw it straight toward you across the leaf. The result will be a clean, true cut, with no pulling or ragged edges. Half leaves, "threes," or "fours" are best for beginners to apply. With these, the cut leaf may be left in position on the cushion, and the outside portion taken off with the tip as required. But if you cut into "quarters," with two crossing cuts, and want to lift one of these "quarters," it must be separated from the rest. The quickest way is to lift them all back [p. 61] into the screen, and then take one up with the knife, turning and blowing it, as if it were a whole leaf, into position at the front of the cushion. But "quarters" are wasteful at best, of both labor and gold; and it is better to use the whole width of the leaf. After one half has been used, the remainder may of course be cut into two "quarters" as readily as into "fours," but at least the first cut from a leaf should ordinarily be used without any further cutting. [pp. 59-62]
The Use of the Tip
The leaf is lifted and placed in position on the panel by the gilder's tip described above. To make the gold adhere evenly to the hairs of the tip, the hairs must be given a thin coating of oil, by drawing the tip over the face or hair. If one's skin and hair are abnormally dry, a trace of Vaseline may be rubbed on the cheek; but this is not usually necessary. Lay the tip against your hair or forehead, and press it down firmly with our left hand, drawing it out slowly with our right hand. Turn it over, and repeat the operation. Do this several times, if necessary, to make the hairs of the tip lie smoothly and sleekly straight. During the work of gilding it may be necessary to treat the tip this way again; but usually it is enough to draw it lightly across your hair or face. This motion, which a gilder performs almost automatically, is often supposed to be made with the idea of electrifying the hairs of the tip. This is erroneous. An electrified tip makes gilding almost impossible; for the gold leaps off the cushion as the tip approaches, and cannot be controlled. Even gilders themselves sometimes believe that they dust the tip across their hair to electrify it; but an experiment with a dry, ungreased tip will convince [p. 63] them of the contrary. Tips should be kept between the leaves of a book when they are not in use, to keep the hairs in order.
To pick up the gold with the tip, hold the tip just above the piece of gold that you want to pick up until you see that the edge of the hairs is parallel with the edge of the gold, and just a little back of it. Then press the tip down with a steady motion upon the gold, and lift it off the cushion. You will find that the gold adheres firmly to the hairs all over, except for a thin edge--say an eighth of an inch, or less--which projects beyond the hairs. If the gold does not adhere to the hairs, press the gold and tip together lightly against the cushion. If it still does not adhere, the tip is not sufficiently greasy. When the tip is in good condition and the gold carefully picked up, this delicate material can be moved about through the air with perfect security and placed in any position. [pp. 62-63]
Laying the Gold
With the gold picked up on the tip, you are ready to begin the gilding proper. Put four ounces or so of cold water into a clean glass, add about an ounce of ethyl alcohol, and stir it well with a good-sized sable brush. With this brush, wet a section of your bole-covered surface considerably larger than the piece of gold which you want to lay. Get it thoroughly wet, and take pains not to rub the surface of the bole with the brush any more than necessary. When it is wet, bring the tip with the gold up close to it, holding it parallel with the panel surface, and sighting the position which it is to occupy. When you have got it directly over the right spot, move the tip toward the wet surface quickly but steadily, and equally quickly move it away again. This motion may require a little practice. It is almost exactly the motion which one uses in testing a hot iron with a wet finger--a touch, and away; but steadiness is important, and the tip must be kept flat, or the gold may be broken.
Some gilders prefer to gild a panel flat, others to tilt it up for gilding to an angle of sixty degrees. The advantage of tilting is that the gilding liquid [water and alcohol, or plain water] may be fed under the gold leaf as it is laid, by bringing a wet brush just up to the edge of the leaf. This flowing water behind the leaf causes all the wrinkles to flatten out, and enables a skilful gilder to manage with less gold. The beginner seldom succeeds with this method. If the flow of water is not kept up constantly, the gesso begins to dry, and the channel closes; water breaks through the gold, instead of staying underneath, and the advantage is more than lost. Keeping the panel flat is generally best for beginners; but it may occasionally be worth while to tilt it up either to drain off any excess of liquid which has collected, or to flow water under any piece of gold which may have gone on badly, so as to float it out on the surface of the liquid.
Assuming that the panel is being gilded flat, the wetting just keeps a little ahead of the gilding. You lay one piece of gold, and then wet the ground for the next piece. In wetting for the second piece, it is a good idea to run the brush just a hair's breadth over the edge of the gold already laid, so that the overlapping portion of [p. 64] the second piece will stick to the first. The same end may be accomplished by breathing rather long and slowly on the space to be gilded immediately before applying the gold. Moisture will then condense on the gold already laid, and the overlap will stick to it. These overlappings usually show a little in the finished gilding, especially as it ages, and they are worth taking a little trouble. Furthermore, since they tend to show, it is desirable to have the pieces of gold carefully cut and neatly applied. Large areas of gilding should be made up as far as possible of uniform pieces, and any odd-shaped bits of gold should be kept back on the cushion for the final faulting. [pp. 64-65]
The order of Gilding
To insure perfect contact between the gold and the bole ground, each leaf should be pressed down with a piece of cotton soon after it is laid. The right time to do this will be learned by experience. If the water is still standing under the gold on the surface of the bole, the pressure of the cotton may force it through the gold leaf, and cause an ugly blemish. If the ground has dried up, pressing with the cotton will do no good. The right moment is when the water has run off or soaked into the ground, and before the ground has begun to dry. In practice you will usually find that this means laying a leaf and then pressing down the second leaf back, or the third or fourth leaf back, according to the speed with which you work and the generosity with which you wet the surface.
Lay the gold in some regular system, in rows from left to right, and top to bottom, ordinarily. This reduces the danger of dropping liquid on the gold which has been laid, and makes for economy in all the operations. Do not try to cut gold too carefully. Begin by making sure that you cut pieces large enough, if you have a certain space to fill. It takes less gold to put on one piece too large than to put on one too small and have to add another to fill it out. Do not try to fit your gold up to too many other pieces. You can fit a piece into one right angle with perfect certainty; but if you try to make it fit two or three right angles, there is grave danger that it will not fit any of them, and you may have to put on two or three pieces to [p. 65] make it come out right. Cut the gold neatly and carefully, but be as generous with it as the saving of labor may require. Remember that the smaller you cut it, the more of it goes into overlaps, and the more it will take to finish the job. If a piece goes on badly, it is often better to take it off with a wet brush and put on another than to try to repair the first. [pp. 65-66]
[Thompson, Daniel V., Jr., Research and Technical Adviser, The Courtauld Institute of Art, University of London. The Practice of Tempera Painting. New Haven: Yale University Press. 1936. Fourth Printing, 1946.]
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