The colours being ground fine in water, and a sufficient quantity of the tints most likely to be employed prepared, they should be arranged in pots or bacons, and several pal lettes with raised edges should be ready at hand to work from, and assist in compounding the varieties of hues neces sary for producing brilliancy and harmony. A few pieces of tile or brick, or of any absorbent some, should also be pro vided, to prove the tints upon, because all colours ground in water become much lighter when dry, than they appear when wet. To be certain therefore of their hue, before lie begins to use than on the picture, and to avoid the trouble and neces sity of much changing or labouring than. (as the painters term the blending of colours,) the artist should apply some of each tint with his brush to the dry brick, &c., which, ab sorning the water, the colours innneiliately appear very nearly of the same hue they will be of when the fresco is dry. I Ienee he may proceed with great security in his work, and is sure to have it much more fresh and vigorous in effect, than it wou.d be it much labour had been employ ed to obtain the tone on the wall.
It \VIII be requisite also to have at hand a vase or bas,tn of water, or a wet sponge. and to take cal e not to begin to paint till the layer of mortar is hard enough to resist the impression of the finger : otherwise the colours would spread upon it, and prevent all possibility of neatness or clearness in the execution, which should be effected with great rapidity and lightness of hand.
With respect to the colours employed in fresco, they are fewer in nuinber than those which may be used in oil paint ing, on account of the combined action of the lime and the air upon the component parts of many of the latter. Those most generally in use are the following, viz. :— Lime -White.—This. when made of well-washed burnt chalk or lime, is the best and most simple white that can be used ; it mixes freely with all the other colours, and works in itself with a full body. The preparation of it requires that the chalk should be slacked a twelvemonth before it is used, or at least, six months. It should then be dissolved in common water, and poured carefully off (after letting it fall some short time.) into a vessel to settle.
Another white is made by mixing one-third of white marble powder with two-thirds of chalk ; but it must be used with caution, as it is apt to change. If the proportion of marble dust be too strong for the chalk, it will become black. The artist will therefore do well to confine himself to i halk white, provided it has been well prepared, and kept a long time. As this. however, has ft equently been used, we deemed it proper to be mentioned, that artists may, if they choose, make experiments upon its nature, and endeavour, if they find any peculiarly valuable quality in it, to ensure its con tinuance in clearness and perfection.
Eyy-shell While.—There is also a third white. made of egg-shells, which, though it has not the full texture of the chalk. is yet very clear and good for use in fresco. It is made by boiling egg-shells in water with a little quick-lime.
They are then put into a pot, and washed with pure water. Then pounded fine, washed again till no tint is given to the water, and then ground by the muller and stone to the degree fit for use ; it is afterwards formed into little cakes, which are dried in the sun. Care must he taken not to let the powder of the shells remain too long in the same water, as it will exhale a fetid vapour almost insupportable. it hich cannot be dissipated but by roasting it in a close vessel, well luted.
Red—produced by burnt vitriol, in colour approaeliir g to Indian red, and ground in spirits of wine. acts well with the lime. resists the action of the air. and mixes clean] V with the other colours. This forms an excellent preparation to receive the bright red of cinnabar or vermilion, when the whole wall is covered.
Colours of earthy textures, such as the ochres. whether burnt or not burnt, umber. both raw and burnt. Spanish red, \'erd de Verona, Venice black. and blue black, made by bruising vine-stalks. or shells of peach-nuts, are all excellent for the purposes of fresco painting.
Blues.—The best is the ultramarine, As it never suffers any change. Smith or enamel blue is good as to preserving its tone. and, if used early in the mark, will adhere but if the ground should become too dry before it is used, it is apt not to incorporate strongly with it, but to come of on the least friction.
White It-ad, lake, verdigris, masticot, Naples yellow, the orpiments, and bone black, are all unfit for this purpose, being liable to change.
Painting in fresco, when carefully- executed, is of all others the most durable, and therefore the most proper to he employed in adorning public buildings. The use of it for this purpose appears to be very ancient. Norden speaks of paintings in Ego ptian palaces SO feet which Winkelman quoting. eoncludes they were in fresco, fiom the description given of the prepared grounds, and of the manner in which the colours appear to have been used. And all the paintings found at Herculanemn, at Portici, and at Home, of ancient date. arc of the same materials. No other kind of painting would so effectually have resisted the action of the air f tr so great a length of time, and more particularly the excessive aridity which those of Herculaneum must have endured, being shut op entirely from the light, and amidst glowing embers from Vesuvius, emitting of course, especially a: first, an intense heat around them. That. however, in one point of view, was favourable to the preservation of those that escaped its immediate action ; for damp is the most powerful destroyer of them, against which no caution taken can make them too secure. in this case of Herculaneum, damp must have been effectually excluded, first by the heat of the ashes, and afterwards, as the stratum of those ashes was so thick, water from above could not penetrate so low as to the pictures, particularly after the upper part was covered with the close cake formed by the decomposed parts, on and near the surface.