The wood usually employed for panels for large pictures was the heart of the female larch. Pliny says, that painters have found by experiment that it is smooth and clean, and not apt to split or warp; he adds that it will last for ever[219]. Theophrastus speaks of the same wood for the same purposes, and also of the cornel[220]. The cedar and cypress appear also to have been used. For smaller pictures it is probable that a greater variety of trees furnished tables for the painter. The tablets used in the schools at Sicyon are said to have been of box-wood. Holly was also particularly fitted for the purpose, by the closeness of its grain and its durability. The earliest modern Italians used also the wood of the fig tree well dried and seasoned[221], besides the larch, ilex, sycamore, and walnut tree. The ancients prepared their boards or tablets with a thin ground of chalk and size of some kind[222], whether a size of flour paste, or weak carpenter’s glue, does not appear. In the thirteenth century the painters took the trouble to make the white for laying grounds themselves. Cennino’s directions on the subject are curious on more accounts than one. He says, “Take the pinion bones and ribs of chickens, the staler the better, and, just as you find them under the table[223], put them into the fire till they become whiter than the ashes themselves.” After this he gives directions to pound, wash and dry them thoroughly, and to keep them in a dry paper for use; he allows certain bones of the sheep also to be used, but, as he always insists on staleness, I suppose he wishes them to be free from grease[224]. Cennino’s boards were prepared with great care, washed with many waters, and pumiced to perfect smoothness; the ground to be laid on thin and rendered smooth and even with the hand, or, as he says, the fat part of the thumb. So far the boards for the school of Sicyon and those for the school of Giotto appear to have been much alike. The next step seems to me also the same. The pupils were to draw very lightly with a metal point--Fuseli calls the antique one a cestrum--upon the white ground, and if anything was amiss it was easily effaced. Cennino directs that the tool should be tipped with silver, whatever metal the main part might be made of, that it should be moderately sharp, and very smooth[225]. We have not any direct evidence that linen cloth or canvass was used to paint upon before the reign of Nero, who ordered an immense portrait of himself to be painted on a linen cloth one hundred and twenty feet in height. Pliny, who relates the fact, does not say whether it were stretched on a frame, or whether it covered planks, to prevent, in some degree, the warping and splitting, to which so many joinings as would have been necessary in a table of that size must have rendered them liable.