A quantity of sulphur being melted in an iro., ow.r the lire, and allowed to flame for five or six minute , is taken ol•, and after cooling a little, is poured in.o the mould ; and the cast having stood a few minutes, lie taken out. Adding a third pal t of vermilion, and shirt' i• the mixture well together, will produce a cast ot a rt., red colon,. \\'h(•n the east is taken limn tl,e mould, it should receive: a polish, from being rubbed over with clean cotton.
Small metallic casts were easily obtained from moulds of plaster, clay, or sand, the latter of which are prefer able for those of larger size- In all cases, particular care must be observed to have the mould pc rfectly dry, otherwise the cast will be disfigured by blow-holes or pores, and the safety of the artist endangered by explo sions, from the rarefaction of the fluids remaining unex pelled. Yet as very few casts of considerable size arc to be obtained free of blow holes, these must necessarily be filled up, either by screwing in a portion of the same substance, or beating it in. The latter is the better me thod, as the interstice: is more completely filled up; but instead of simply filling op the pore in the cast taken from the mould, the detect is More completely cm cd, by enlarging it somewhat more, and then beating in a piece of metal. if the cast has to undergo a considerable change after coming from the mould, it should be beat over the whole surface with a hammer of a few ounces weight, which will close all the small blow-holes, and fit it for receiving a suitable polish. This method can not be adopted where a complete and perfect figure from the mould is desired.
Equal quantities of pumice-stone and plaster of Paris, with a third of clay, is considered a suitable composition for moulds to receive small metallic casts ; ar two parts of fine brick-dust, added to four of plaster, and mixed up with water until of the consistence of cream. Supposing a snn,ll animal, a bird, frog. or lizard. is to be imitated, the subject, after being moistened with spirit of wine. is to be suspended by threads, in a trough or frame, w bleb must toes be lilted with the composit,on. But a chan nel to the cavity w hich the subject occupies must be preserved by a strong thick wire. proceeding from its extremiti to above the surk.ce of 1,,e composit:on. This, when wit .drawn. leave a conduit for receiv ing the metal. Ot,.er vents are necessary. in all moul(Is, large or small, for allowing the included air to escape.
su'iiect t;.us remaining- included, and the wires be ing w:t. 'drawn, the mould must be gradually exposed to successive degrees of heat, until becoming red hot, wher,..hv the su:)ject will be totally consumed. and a cavi ty ItIt, corresponding to the space occupied by its parts.
But as SJme partic.es of lust or ashes may remain after eN cry precaution to discharge tacm, the cavity should be filled with mercury, by v nich means they will ripe on Cie surface. and may be poured out along with it. The mould, when converted to use, must be rendered very hot, and gentle struck after receiving the metal. that access may be gained to all its parts, and the e xpul sion of air facilitated. After being allowed a sufficient time to the cast is removed.
Metallic casts of large subjects, are great and impor tant works, wherein the concurrence of many different circumstances are essential to the success of the artist. The ancients were well acquainted with the various me thods practised in casting in bronze, as appears from the beautiful relies still preserved to us, and the description of the busts and statues of divinities in their temples. It has been conjectured, however, that none of them were of extraordinary size ; that they were in general little if any larger than life, and that the colossus, celebrated as one of the wonders of the world, could only have been formed of plates of metal. Some of the moderns have peculiarly excelled in this branch of the arts, and have themselves minutely laid down the rules whereby to ob tain a successful metallic cast.
Here, as in all other cases, a model of the cast is built on a skeleton, composed of wood or iron, exhibiting the angles and curvatures of the figures desired. The fa mous artist, Benvenuto Ccllini, affirms, that this skele ton should be covered, to nearly the size of the figure, with clay, well beaten together with a quantity of rags, by an iron rod, and the mixture thus kept several months to macerate. It will then form a paste, which may be wrought up with the hand, and is fashioned into shape. When sufficiently baked, and having been allowed a considerable time to dry, that no contraction may en sue on subsequent heat, this rude resemblance of what is to be cast is covered with a coating of wax, not less than an inch thick, on which the artist impresses the ex act form of what the cast is meant to exhibit, and var nishes over the surface. A mould is next prepared of plaster, or of a mixture of clay and sand, which it is ex ceedingly difficult to procure of suitable quality, and from this cause the works of skilful statuaries have failed ; and being applied around the model, is allowed to be come perfectly dry. This mould, it is evident, is to re ceive the cast, but a different proceeding from taking it to pieces is employed to obtain a cavity. It is perfo rated by innumerable channels through the clay to the surface of the model, which also are all filled up with wax. The greater the number, the more is the chance of success.