You ask whether the rough cast on the wall must be scraped off before you wash the wall for painting. If by the _rough cast_ you mean rough plaster, which is a totally different thing to rough cast, certainly use it as it is. The coarser the plaster the better, because it is all the more porous, so long only that it is of the best materials (viz. perfectly _washed_ sand, and good lime), and well put on a good wall. _Nothing in the world could equal it for painting upon_, except a surface of _coarse clean_ Bath stone, with _all its pores open_. If you have such plaster as I have just described, and both it and the wall thoroughly dry, nothing could be better. The smooth surface, with what granulated texture you please, can be got according to the directions in my paper--viz. after two or three washes of pure diluted medium, give another or two more of the same, with dry whiting and a little white-lead, then go ahead _while it is all fresh_, viz. _two or three days_ after the process of preparation has been completed. Take care in painting not to rub it up too much, for fear of _drawing up the glossy resins to the surface_ away from the wax. Paint right _into_ your prepared surface _solidly_ and with _decision_ in the way of fresco painting, not as oil. Keep the brush clean, and the volatile oil in the dipper clean, and then, oh! how shall I envy you your power to use them all![30] At the _Ely ceiling_, which is of hard wood _not_ porous, but prepared with three coats of oil white-lead, I am painting with Liquid Measure. Pale drying oil 2 Japan gold size 2 Turpentine 2 Artist copal 1 well shaken up every time it is used. The colours are all ground up in it, and then painting is done as in water-colour, using _pure spirits of turpentine_ as a vehicle. Colours dry extremely rapidly and with a dead surface. The stuff looks horribly black, but the colours are not materially affected by it. Of course it is not to be compared with my former medium, because there is that bane of the palette oil in it, but I used it because of its great facility (used transparent like _water-colour on a white ground_), and because the surface was hard, so that wax might (in great heat) shrink or play tricks on it, as it has done in Murillo's pictures and many others.--Ever most sincerely yours, T. GAMBIER PARRY. If I can do anything for you, command me; we go to Scotland on the 14th. LONDON, _April 26, 1863_.