Page:The Annual Register 1758.djvu/398

 a part of it should be spread on a linen cloth, of the size of the painting, where it should be suffered to set and dry; and then another coat put over it: when this is become stiff also, the glue should be again heated; and while it remains of such heat as to be easily spread, it should be laid over the face of the picture, and a linen cloth immediately put over it in the most even manner, and nailed down to the picture and table at the edge likewise. The glue should not be used boiling hot, as that would hazard some of the delicate colours of the painting; and the linen cloth should be fine and half worn, that it may be the softer, and lie the flatter on the surface of the picture; in order to which it is proper to heat it till the glue be soft and pliable before it be laid on, and to compress each part gently with a ball formed of a linen rag tied round with thread. The table, with the picture, cloth, &c. nailed down to it in this state, should be then exposed to the heat of the sun, in a place where it may be secured from rain; and there continued till the glue be perfectly dry and hard; at which time the nails should be drawn, and the picture and linen cloth taken off from the table. The picture must now be again turned with the face downwards, and stretched and nailed to the table as before; and a border of wax must be raised round the edge, in the same manner as is directed for the copper-plates, forming as it were a shallow trough with the surface of the picture; into which trough should be poured a proper corroding fluid, to eat and destroy the thread of the original canvas or cloth of the picture. The corroding fluid used for this purpose, may be either oil of vitriol, aqua fortis, or spirit of salt; but the last is preferable, as it will more effectually destroy the thread, when it is so weakened by the admixture of water as not to have any effect on the oil of the painting; which ever is used, it is necessary they should be properly diluted with water; to find the due proportion of which, it is expedient to make some previous trials; and when they are found to be of such strength, as to destroy the texture of thread, without discolouring it, they are in the due state. When the corroding fluid has done its office, a passage must be made through the border of wax at one end of it; and the fluid must be poured off, by inclining the table in the requisite manner and the remaining part must be washed away, by putting repeated quantities of fresh water upon the cloth. The threads of the cloth must then be carefully picked out till the whole be taken away: but if any part be found to adhere, all kind of violence, even in the least degree, must be avoided in removing them: inftead of which, they should be again touched, by means of a pencil, with the corrosive fluid less diluted than before, till they will readily come off from the paint. The reverse furface of the painting, being thus wholly freed from the old cloth, must be then washed with water, by means of a sponge, till the corroding fluid employed be thoroughly cleansed away; when being wiped with a soft sponge till all the moisture that may be collected by that means be taken off, it must be left till it be perfectly dry. In the mean time a