In this volume the receipts for the most part are to be met with in the body of the work under the various processes in which they are to be used, but a few remarks upon the materials which analyses disclose the use of, and a few receipts for gilding grounds, may fitly occupy the place of this section.
First a receipt from a Byzantine MS. for wax painting by Didron:—Take size, a strong solution of potass and white wax in equal quantities, mix together and place them on the fire to dissolve. Add colour to the mixture; dilute the tint well and paint with a brush. Let the colour dry and then you can give it a polish. Gilding, if you use any, will become very brilliant; it is useless to add varnish. (He says the monks of Mount Athos still use this receipt).
Mrs. Merrifield says that the paintings on the walls of the chapel of S. Jacopo di Pistoia were ascertained by Professor Branchi to have been executed on a ground composed of sulphate of lime (plaster of Paris), carbonate of lime, and a yellowish colouring matter tempered with glue. It has also been ascertained that many of Luini's paintings in the Monastero Maggiore are not " buon fresco/' but painted on white stucco in the ancient manner. The MS. of Alcherius gives the following directions for painting walls:—"Put a little lime with ochre that it may be lighter coloured, or mix it with simple red or ' prasin,' or with a colour which is called ' posce,' which is made of ochre, green, and 'membrayne'; or you may take of a colour which is made of sinople, ochre, lime, and ' posce,' etc. And walls should be painted rather moist than otherwise, because the colours unite together better and are firmer. And all the colours for walls should be mixed with quicklime (!)." This is probably the method of mural painting generally practised in the Middle Ages.
The mordant for gilding on walls and places exposed to damp was oil. Professor Branchi analysed some of the grounds of Benozzo Gozzoli's pictures where gilded. The intonaco was white and fine—a " denaro " (1*779 grammes) contained 0*576 gramme of a fine white sand mixed with a little argillaceous earth. The gilding in a picture by Buffalmacco is spread upon a layer of wax about half a line thick. (There was no indication that drying oil was mixed with it.) The gilding was probably executed (1) by applying on the smooth intonaco a kind of size soluble in water and yellow in colour; (2) by applying a thin coating of wax on this, to which the gold leaf was affixed. The wax must have been dissolved in a volatile oil.
If you wish to lay gold on a wall, or on paper, or on wood, or upon a block of marble, grind gypsum by itself separately. Then grind brown separately in the same manner, and take three pints of gypsum and one of brown, and take glue made from parchment or leather, and distemper them together, mixing the said parts, and lay upon it (the object) one coat of this mixture with a paint-brush and then another; and so lay three or four coats. And when the last is dry, scrape it with a knife or other iron instrument fitted for the purpose, so that it may be very smooth; and then burnish it with a tooth or stone, and lay over it with a paintbrush only one very thin coat of the gypsum and let it dry. When it is dry lay the gold upon that mordant as you have been taught. Afterwards lay upon the gold a very fine cloth that has been two or three times warmed; or apply it as I do, not so warm, in order that the gold may be the better polished.
Take gypsum and grind it well with water. Then take your glue, which is made of bull skin, and mix with it a little white of egg, and distemper the gypsum. But when you wish to lay on the gold cover the place with gypsum with a brush and let it dry. Do this three times. Then scrape it that it may be smooth and burnish it, and again lay another coat of the glue or mordant upon it, and then your gold upon that, and remove the dirt gently with cotton, and then let it dry. But if you wish to polish it, do so with haematite or with a dog's tooth.
Take brasilium newly distempered, with white of egg well whipped, with a sponge or otherwise, and draw and paint with it whatever you like on vellum or on any other thing you wish to gild, and immediately lay the gold upon it, and remove the dirt with cotton, scarcely * touching it, and leave it to dry for half a day or a whole day if you like. Then take a dog's tooth and begin to burnish at first gently, lest you should spoil it all, and then harder, and afterwards so hard that your forehead is wet with perspiration.
But take notice that you ought to work in gold and colours in a damp place on account of the hot weather, which, as it is often injurious in burnishing gold, both to the colours on which the gold is laid and in the gilding, if the work is done on parchment that is too dry and not sufficiently moist; so also it is injurious when the weather is too dry and arid, or too damp while applying colours or* gilding.
Take calcined bone, ground fine with weak glue, such as parchment glue, and let it dry; and when quite dry grind it up afresh with linseed oil and make it rather stiff; then take a little " liquid varnish " and incorporate it with the bone dust. Add to it a little saffron, sufficient to give it colour and make it rather stiff. When you wish to put the gold on the wall the mortar must be dry, and the mordant must not be applied too thick. Let it remain five or six days and then put on the gold.