Take litharge, verdigris, and a little ochre, and grind them with a little linseed oil and " liquid varnish," incorporate them well together, and then gild in the usual manner.
Gilding was often imitated by the use of less costly materials, such as silver or tinfoil varnished over with a yellow varnish or lacquer, the " sandarac " varnish so often mentioned in books on the beginnings of oil painting. At S. Jacopo, Pistoia, note is made of the use of thirty-seven pieces of tin, in the fifteenth century, while 7,000 leaves of gold were used. From one ounce of gold the Roman gold-beaters obtained 750 square leaves and upwards, four fingers broad, as Pliny relates. Modern gold-beaters make 1,200.
Cennini complains that in his time 145 leaves were obtained from a ducat in place of 100, and Vasari says that 435 leaves were made from three ducats, the same proportion.
A composition of quicksilver, tin, and sulphur, called " porporino," was used to imitate gold, and Jehan le B&gue gives full details of how to make " auripetrum," the tin with the varnish over it. " Spanish saffron, distempered with very clear glue or liquid varnish, and laid over very clear, that is, very bright and well-polished tin, assumes the appearance of gold to those that look on it, for it receives its colour from the sun, and its brilliancy from the tin, and thus may be made excellent auripetrum " Another receipt says that the saffron flowers should be treated with white of egg, into which the tin leaves are to be dipped three times, drying between and then polished with onyx and greased with linseed oil; and another gives myrrh and aloes, equal parts by weight, boiled together, as the colouring medium, into which the tin leaves varnished are to be dipped, and subsequently into a similar decoction of the middle bark of the black plum; and yet another gives linseed oil and resin and " vernix " (sandarac varnish).
Take a pound of lime and twelve pounds of wood ashes; then take boiling water and put the whole together, making them boil well; after which let the mixture settle and strain it through a cloth. Then take four pounds of that water, heat it well, take about two ounces of white wax and put this to boil with the water, then take about half an ounce of fish glue, put it in water, and leave it until it is well softened, and, as it were, melted, when you must manipulate it until it becomes like paste, and throw it into the water with wax and make all boil together; then add to it about half an ounce of mastic and boil it with the other ingredients. Take some of this water on a knife-blade or a piece of iron to ascertain whether it be done; if it is like glue it is all right. Strain this water while hot or tepid through a linen cloth, let it settle and cover it well. With it you may distemper all kinds of colours.
No. 347. Water in which Unseed oil has been steeped for a day and a night receives a glutinous quality from that seed which makes it proper for tempering colours.
No. 318 gives fish glue dissolved in good white wine as a medium for gilding on a ground of gypsum and sinople. This is somewhat akin to Pliny's "Leuco-phoron," a cement used for applying gold leaf to wood.
It was made of half a pound of Pontic sinopis. ten pounds of bright" sil" (attic ochre), and two pounds of Greek " melinum" (a white earth), well mixed.
S. Forni gives the following receipt for putting lines of gold and silver on draperies or feigned reliefs: Make a mordant of wax, purified suet or tallow, gum el&ni, turpentine, and mastic, in equal proportions, except the suet, which is to be half. Melt them gently in a pot, stirring with a wooden spatula. Then with a fine brush, and this mixture diluted with half its weight of essential oil of pine, draw the lines. When it is dry enough to be sticky apply the gold or silver. The next day dust off the superfluous metal with a soft brush of beaver or badger. If you cannot see the lines you are drawing you may stain the colour, with dragon's blood or minium ground very fine with essential oil of pine.
If the gilding is to be laid on aureoles or ornaments raised in plaster, give the surface two coats of size, and then with a mordant paint the shapes; leave it for twenty-four hours and then apply the gold leaf. The following two mordants are good, he says : together and triturated for twelve successive days.
Boiled oil . 339 grammes.
Venice turpentine . .112
Naples yellow . . . 140
Warm the oil and mix the turpentine carefully with it, then add the Naples yellow ground in a little oil.
Boiled oil . . .112 grammes.
Yellow ochre . . .56 Minium . . 28
Copal varnish . 56
Grind the ochre and minium together with the oil, then add the varnish. It does not last so well as the other, but can be gilded immediately.
Boiled oil mixed with yellow ochre and Armenian bole, ground together in equal parts to the consistency of syrup, may also be used. It is best when it has been kept a good while.
For making u caseum" for cheese tempera S. Forni gives the following:It may be prepared by adding a little carbonate of potash or of soda to curds, but it is better to press the curds through a sieve or to dry them in a cloth to get rid of all the whey. Ammonia added makes a viscous cream which may be diluted with water. Keep the " caseum " dry in a glass bottle well stoppered, and mix with ammonia as required, first softening it with warm water.
Fig juice should be collected in October, and kept dried in drops in a glass bottle. When required as a mordant for gilding mix it with wine or liquid ammonia.
Blues and blacks made from charcoal require size as a medium. Yolk of egg makes the former green, and the latter do not dry properly.
Punches used for stamping patterns on gilded surfaces are better made of ivory than of either iron or steel.