If you have not a bladder (of the sturgeon), cut up thick parchment or vellum in the same manner,--wash and cook it. Prepare also the skin of an eel carefully scraped, cut up and washed in the same manner. Prepare thus also the bones of the head of the wolf-fish washed and dried, carefully washed in water three times. To whichever of these you have prepared, add a third part of very transparent gum, simmer it a little, and you can keep it as long as you wish. CHAPTER XXXIV. HOW COLOURS ARE TEMPERED FOR BOOKS. These things thus accomplished, make a mixture of the clearest gum and water as above, and temper all colours except green, and ceruse, and minium, and carmine. Salt green is worth nothing for books. You will temper Spanish green with pure wine, and if you wish to make shadows, add a little sap of iris, or cabbage, or leek. You will temper minium, and ceruse, and carmine, with clear of egg. Compose all preparations of colours for a book as above, if you want them for painting figures. All colours are laid on twice in books, at first very thinly, then more thickly; but twice for letters. The next extract I give is of great interest in the technical history of illumination, on three accounts: firstly, because it guides the student to recognize in madder the purple stain and colour, so highly prized in the early periods of the art; secondly, because it shows him the manner in which fugitive vegetable tints were protected from the decomposing influence of the atmosphere by an albuminous varnish; and thirdly, because it illustrates the ordinary modern processes of under painting, and glazing with transparent colour. The "folium" of the Greek illuminators was procured from plants growing abundantly near Athens, while that of the Hiberno-Saxon scribes was obtained from the "norma" or "gorma" of the Celts. Mr. Hendrie, in his learned notes to Theophilus, has traced successive recipes for the preparation of "folium," in which the identity of the base giving the colouring matter is clearly established. It is curious that the collections of "Secreta" should give as the only countries supplying the materials for making "folium," those two in which the use of the bright purple stain ascends to the very earliest of their decorated manuscripts. The following is the description given by Theophilus:-- CHAPTER XXXV. OF THE KINDS AND THE TEMPERING OF FOLIUM.