This kind of compo, or stucco, is frequently used by plas terers for cornices and mouldings, in the same manner that has already been described in common plastering. But here, the workman finds requisite to add a small portion of plas ter of Paris, to make it fix better while running or working the mould. Such addition, however, is not calculated to give strength to the stucco ; and is only made through the necessity of having a quick set.
Some years ago, the patent stucco of Dr. B. Higgins, was in great repute, and employed by the founders of the Adelphi, in the Strand, with considerable success. It consisted of 141b. or 151b. of good stone lime, 1 -11bs of bone-ashes, finely powdered, and 951b. of clean sand, coarse or fine, according to the intended nature of the building : these were mixed up into mortar as quickly as possible with lime-water, and used as soon as made.
The various suggestions and modes of firming the same materials into stucco, amount to about forty in number, only varying the proportions; but few of them have been found to remain tolerably entire in this climate for thirty years together. In 1796, Mr. Parker obtained a patent for a cement that is impervious to water, and may be success fully employed in ice-houses, cisterns, tanks, &c. (See CEMENT, and :\lonrait.) In his specification, Mr. Parker observes, "nodules of clay, or argillaccous stone, generally contain water in their centre, surrounded by calcareous crystals, and having veins of calcareous matter. They are formed in clay, and are of a brown colour, like the clay." These nodules, he directs, should be burned, after being broke into small pieces, in a kiln, with a heat nearly sufficient to vitrify them ; after which they are to be reduced to pow der. Two measures of water added to five of this powder, produces /arras; lime and other matters may be added or withheld at pleasure: and the proportion of water may be varied. The term of the patent being now expired, there are many other intIllUfilettll'es of this cement, which are found to be of equal goodness as to quality, and some of them of rather a better colour than the ; a or rather improvement, of considerable importance, since the fresco-painting, or whitewash, laid upon Parker's com position, applied to the fronts of houses, is soon taken uff by the rains, and leaves the walls of a dingy and unplea appearance.
An allusion has been made above, to the fresco-painting, or staining„, laid upon walls plastered with this cement ; this is done to give them au appearance of stone-buildings, and is performed by diluting sulphuric acid (oil of vitriol) with water, and adding the fluid ochres, &e., to give the required tint. When the stucco is washed over with this kind of paint, the affinity existing in the iron of the cement ceases, the acid and colour suspended in and upon the stucco is fixed, and the surface assumes, when dexterously managed, the appearance of an ashlar bond of masonry.
Columns, &c. done in Scagliola, is a distinct branch of plastering, discovered or invented in Italy, where it has been much used, and thence introduced into France, where, having fascinated all the cognoscenti, it obtained the title of seugliola. '1 he late Henry I Iolland, who first brought it to England, engaged the artists from Paris to execute it ; sonic of whom, finding a demand here for their labour, remained in the country, and instructed our own workmen in the art. Columns and pilasters are executed in this branch of plas tering, in the f dlowing manner. A wooden cradle, composed of thin rips of deal. or other wood, is made to represent the column designed, but about ..??, inches less in diameter than the shaft is intended to be when finished. This cradle is lathed rotund, as for common plastering, and then covered with a pricking-up coat of lime and hair : when this is quite dry, the artists in seagliola commence their operations, and, by an of the niost rare and precious marbles, pro duce a most astonishing and delusive effect; for, nothing short of actual fracture can discover the countel felt and any stone, partaking of the quality of marble, may be exactly imitated by it ; the imitation taking as high a polish, and feeling to the touch as cold and solid, as the most com pact and solid marble. The workmen select the purest gypsum they can obtain, which, after breaking it into small pieces, they calcine. As soon as the largest fragments lose their brilliancy, the fire is withdrawn ; the calcined powder is passed through a very line sieve, and mixed up as it is to be used with is soltition of Flanders glue, isinglass, &c. In this solution the colours required in the marble to be imitated are also diffused : but when the work is to be of various colours. each colour is separately prepared, and they are afterwards mingled and eombined, nearly in the same man lier that a painter mixes the primitive colours on his palette, to compose his different tints. When the powdered gypsum is prepared and mingled for the work, it is laid on the shaft of the column, &c. over the pricked-up coat of lime and hair, and then it is floated with moulds of wood, made to the requisite size, the artist using the colon N necessary for the itnitation during the floating, by which means they become mingled and incorporated with the surflice. To give the work the requisite polish, or glossy lustre, so touch admired in works of marble, the workman rubs it with a pumice. stone with one hand, while with the other he cleans it with a wet sponge. lle then polishes it with tripoli and charcoal and fine soft linen ; and after going over it with a piece of felt dipped in a mixture of oil and tripoli, he finishes the process by the application of pure oil.