A convenient preparation for the use of artists, invented by Mr. George Blackman, for which that gentleman was awarded a medal by the Society of Arts. Take, says Mr. Blackman, of the clearest gum mastich, reduced to fine powder, four ounces; of spirits of turpentine, one pint; mix them together in a bottle, stirring them frequently till the mastich is dissolved: if it is wanted in haste, some heat may be applied, but the solution is best when made cold. Let the colours to be made use of be the best that can be procured, taking care that by washing, etc. they are brought to the greatest degree of fineness possible. When the colours are dry, grind them on a hard, close stone, (porphyry is the best,) in spirits of turpentine, adding a small quantity of the mastich varnish. Let the colours so ground become again dry, then prepare the composition for forming them into cakes in the following manner: - Procure some of the purest and whitest spermaceti you can obtain; melt it over a gentle fire in a clean earthen vessel; when fluid, add to it one-third of its weight of pure poppy oil, and stir the whole well together; these things being in readiness, place the stone on which your colours were ground on a frame or support, and by means of a charcoal fire under it make the stone warm; next grind your colour fine with a muller, then adding a sufficient quantity of the mixture of poppy oil and spermaceti, work the whole together with a muller to a proper consistence; take then a piece of a fit size for the cake you intend to make, roll it into a ball, put it into a mould, press it, and it will be complete.
When these cakes are to be used, they must be rubbed down in poppy, or other oil, or in a mixture of spirits of turpentine and oil, as may best suit the convenience or intention of the artist.