CHAP. II.
Of the means of taking calls, and impreffions figures and bufls, medals, leaves, &c.
TH E method of taking calls of figures and bufls, as at prefent pradtifed, is moft generally by the ufe of plafter of Paris; or, in other words, alabafler calcined by a gentle imprefTions, from heat.
The advantage of ufing this fubfiancC preferably to others, confifts in this, that not* withftanding a flight calcination reduces it to a piilverine ftate, it becomes again a tenacious and cohering body, by being moiftened with water; and afterwards fuffered to dry j by which means either a concave or convex figure may be given by a proper mold or model to it when wet, and retained by the hardnefs it acquires when dry: and from thefe qualities, it is fitted to the double ufe of making both caftsy and molds for forming thofe cafts. The pla- ' fter is to be had ready prepared of thofe, who make it their bufinefs to fell it, and the only care is to fee that it is genuine.
The particular manner of making cafts depends on the form of the fubjeCt to be taken. Where there are no projecting parts, it is very fimple and eafy ; as likewife where there are as fuch form only a right or any greater angle withtheprincipalfurfaceof the body: but where parts projeCt in lefler angles, or form curves inclined towards the principal furface of the body, the work is more difficult. I fhall therefore firft explain thofe particulars of the manner, which are general to all kinds; and then point out the extraordinary methods to be ufed where difficulties occur.
The firft ftep to be taken is, the forming the mold; which is, indeed, done by much the fame means, as the caft is afterwards made in it. In order to this, if the original or model be a bafs-relief, or any other piece of a flat - form, having its furface firft well greafed, it muft be placed on a proper table, or other fuch fupport; and furrounded by a frame, the fides of which muft be at fuch a diftance from it, as will allow a proper thicknefs for the fides of the mold. A due quantity of the plafter, that is, what will be fufficient to cover and rife to fuch a thicknefs as may give fufficient llrength to the mold, as alfo to fill the hollow betwixt the frame and the model, muft be tnoiftened with water, till it be juft of fuch confiftence as will allow it.to be poured upon the model j which ffibuld be done as foon as poffible: for it muft not be delayed after the water is added to the plafter, which would otherwife concrete or fet, fo as to become more troublefome in the working, or unfit to be ufed. The whole muft then be fuffered to remain in this condition, till the plafter has attained its hardnefs; and then the frame being taken away, the preparatory caft or mold thus formed may be taken off from the fubjedt intire. >
Where the model or original fubjedt' is of a round or eredt form, a different method muft be perfued; and the mold muft be divided into feveral pieces: or if the fubjedt con- lifts of detached and projedling parts, it is frequently molt expedient to caft fuch parts le- parately; and afterwards join them together. - Where the original fubjedt or model forms a round, or fpheroid, or any part of fuch . - round, or fpheroid, more than one half, the plafter muft be ufed without any frame to keep it round the (model; and mud be tempered, with water, to fuch a canlkftence, that it may be wrougnt with the hand like very foft pafte: but though it mud not he fluid, as when prepared for flat flgured models, it mull yet be as moift as if compatible with its cohering diffidently to hold together: and being thus prepared, it muft he put 'upon die model, and compneffed with the hand, or any flat inftrument, that the parts ■of it may adapt ihemfeives, in the moil perfect manner, to thole of the fubjedt, as well as he compad with aelped to themfelves. When the model is lo covered to a convenient thickneis, the whole muft be left at reft till dié plafter be let and Arm, fo as to bear dividing without falling to pieces; or being liable to be put out of its form by flight violence: and it muft then be divided into pieces, in order to its being taken off from the model, by cutting it with a knife, or with a very thin blade j and being divided, muft be cautioufly taken off, and kept till dry: but it muft be always carefully obferved, before the feparatioh of the parts be made, to notch diem crols the joints, or lines of the divifion, at proper diftances, that they may with eafe and certainty be properly conjoined again; which would be much more precarious and troublelome without fuch diredive marks. The art of properly dividing the molds, in order to make them fepa- ratc from the model, conftitutes thegreateft ob-je£t of dexterity and /kill in the art of carting; and does not admit of rules for the moft advantageous conduct of it in every cafe: but I {hall endeavour to explain the pinciples on which it depends in fuch manner, that by a due application of them, all difficulties may at any time be furmounted, and an expertnefs even of manner acquired by a little practice. With refpeCt to the cafe in queftion, where the fubjeCi is of a round or fpheroidal form, it is beft to divide the mold into three‘parts, which will then eafily come off from the model : atid the lame hold good of a cylinder, or any regular curve figure.
The mold being thus formed and dry, and the parts put together, it muft be firft greafed and placed in l'uch a pofition that the hollow may lie upwards, and then filled with plafter commixt with water, in the fame proportion and manner as was directed for the carting the mold: and when the cart is perfectly fet, and dry, it muft be taken out of the mold and repaired, where it is neceffary: which finilhes the whole operation.
This‘ is all that is required with refpeCt to fubjefts, where the furfaces have the regularity above mentioned: but where they form curves which interfeCt each other, the conduct of the operation muft be varied with re- IpeCt to the manner of taking the caft of the mold from off the fubjeCt or model j and where there are long projecting parts, fuch as legs or arms, they Ihould, as was obfcrved be- . fore, be wrought in feparate calls.
The method of dividing properly the molds cannot be reduced, as I intimated, to any particular rules; but muft depend in fome degree on the fkill of the operator, who may eafily judge from the original fubjeCts, by the means here fuggefted, what parts will come off together ; and what require to be feparated: the principle of the whole confifts only in this, that where under-workings, as they are called, occur, that is, where-ever a ftreight line drawn from* the bafis or inlertion of any projection, would be cut or eroded by any part of fuch projection, fuch part cannot be taken off without a divilion: which muft be made either in the place where the projection would crofs the ftreight line; or, as that is frequently difficult, the whole projection muft be feparated from the main body and divided alfo length ways into two parts: and where there are no projections from the principal furfaces, but the body is fo formed as to render the furface a comr pofition of fuch curves, that a ftreight line being drawn parallel to the furface of one part would be cut by the outline, in one or more places, of another part, axlivifion of the whole ffiould be made, fo as to reduce the parts of it jnto regular curves, which muft then be treated as fuch.
Where detached parts of a long form, as ' legs, arms, fpears, fwords, &c. occur in any figure, they fhould be caft in feparate molds: and if fuch parts are of a compound ftruChire, the fame rules, as was before intimated, muft be obferved in the management of them, as are already directed for the principal part.
. In larger mafles, where there would other- wife be a great thicknefs of the plafter, a corps or body may be put within the mold, in order to produce a hollow in the call j which both faves the expence of the plafter, and renders the caft lighter.
This corps may be of wood, where the forming a hollow of a ftreight figure, or fuch as is conical with the bafis outward, will anfwer the end: but if the cavity require to be round, or of any curve figure, the corps cannot be then drawn while intire; and confequent- ly Ihould be of fuch matter as will fuffer itfelf to be taken out piece meal. In-this cafe, there* fore, the corps is beft formed of clay: which muft be worked upon wires to give it tenacity ; and fufpended in the hollow.of the mold, by crofs-wires lying over the mouth: and when the plafter is fufficiently let to bear handling, the clay muft be picked put by a proper inftrument.
. Where it is defired to render the plafter harder-, the Water with which it is tempered fhould be mixed with parchment fize prepared as below directed j which will make it very firm and tenacious. .
In the fame manner figures, bulls, &c may be caft of lead, or any other metal, in the molds of plafter; only foe expence of plafter, and the tcdioufnefs of its becoming fufficiently dry, when in a very large mafs, to bear-the . A heat of melted metal, render the ufe of clay, compounded with fome other proper materials, preferable where large fubjedts are in queftion. The clay, in this cafe, Ihould be wafhed over till it be perfectly free from gravel or ftones; and then mixed with a third or more of fine fand to prevent its cracking: or, inftead of fand, coal a files lifted till they be perfectly fine is preferable. Whether plafter, or clay, be ufed for the calling in metal, it is extremely necef- fary to have the mold perfectly dry; other wife, the moillure, being rarificd, will make an ex- plofion, that will blow the metal out of the mold, and endanger the operator, or at leall crack the mold in fuch manner as to frullrate the operation. Where the parts of a mold are larger or projedl much j and confequently require a greater tenacity of cohefion of the matter they are formed of to keep them together, flocks of cloth, prepared like thofe defign- ed for the paper hangings, or fine cotton pluckt . or cut till it is very fhort, fhould be mixt with the alhes or fand before they be added to the clay to make the compolition for the mold. The proportion Ihould be according to the degree of cohefion required: but a fmall quantity will anfwer the end, if the other ingredients of the compolition be good ; and the parts of the mold properly linked together by means of the wires above diredted.
There is a method of taking calls in metals from fmall animals, and the parts of vegetables, which though not much known or ufed in this country, may be neverthelefs pradtifed for fome purpofep with advantage; particularly for the decorating grottoes or rock work, where nature is imitated. The proper kinds of animals are lizards, fnakes, frogs, birds, or infedts j the calls of which being properly coloured will be exact reprefentations of the originals.
This is to be performed by the following method. A coffin or proper cheft for forming the mold, being prepared of clay, or four pieces of boards fixed together, the animal or parts of vegetables, muft be fufpended in it by a firing ; and the leaves, tendrils, or other detached parts of the vegetables, or the legs, wings, &c. of the animals, properly feparated and adjufted in their right pofition by a fmall pair of pincers; and a due quantity of plafler of Paris, and calcined talc, in equal quantities, with fome alumen plumofum, muft then be tempered with water to the proper confidence for calling; and the fubjedt from whence the caft is to be taken, as alfo the fides of the coffin moiftned with fpirit of wine.
The coffin or cheft muft be then filled with the tempered compofition of the plafler, and talc, putting, at the fame time, a piece of ftreight flick or wood to the principal part of die body of the fubjedt, and pieces of thick wire to the extremities of the other parts, in order, that they may form, when drawn mit after the matter of the mold is properly fet and firm, a channel for pouring in die a melted metal, and vents for the air j which otherwife by the rarefa&ion it would undergo from the heat of the metal, would blow it out or bur ft the mold. In a fhort time the plafter and talc will fet and become hard; when the ftick and wires may be drawn out; and the frame or coffin in which the mold was call taken away: and the mold muft then be put fir ft into a moderate heat, and afterwards, when it is as dry as it can be rendered hy that degree, removed into a greater j which may be gradually increafed, till the whole be red hot. The animal, or part of any vegetable, which was included in the mold, will then be burnt to a coal ; and may be totally calcined to afhes, by blowing for fome time gently into the channel and paflages made for pouring in the metal, and giving vent to the air j which will, at the fame time that it incinirates the remainder of the animal or vegetable matter, blow put the afties. The mold muft then be fuffered to cool gently; and will be perfect; the deftrudtion of the fubftance of the animal or vegetable, having produced a hollow of a figure correfpondent to it: but it may be ne- verthelefs proper, to fhake the mold, and turn it upfide down, as alfo to blow with the bellows into each of the air vents, in order to free it wholly from any remainder of the afhes : or, where there may be an opportunity of filling the hollow with quickfilver without expence, it will be found a very effectual method of clearing the cavity, as all duft, afhes, or fmall detached bodies, will neceflarily rife to, the furface of the quicklilver j and be poured out with it. The mold being thus prepared, it muft be heated very hot when ufed, if the caft be made with copper or brafs : but a lels degree will ferve for lead or tin: and the matter being poured in, the mold muft be gently ftruck; and then fuffered to reft till it be cold; at which time it muft be carefully taken from the caft j but without the leaft force, for fuch parts of the matter as appear to adhere more flrongly, muft be foftned by foaking in water, till they be intirely loofned, that none of the more delicate parts of the caft may be broken off or bent.
Where the alumen plumofum, cr talc, cannot be ealily procured, the plafter may be ufed alone; but it is apt to be calcined by the heat ufed in burning the animal or vegetable from whence the caft is taken; and to become of too incohering and crumbly a texture: or for cheap- nels Sturbridge clay, or any other potters or other good clay, wafhed over till it be perfectly fine, and mixed with an equal part of fand and fome flocks cut fmall, may be employed. Pounded pumice ftone and plafter of Paris, taken in equal quantities and mixed with wafhed clay in the fame proportion, is faid to make excellent molds for this and parallel ufes.
Cafts of medals, or fuch fmall pieces, as are of a fimilar form, may be made in plafter, by the method directed for.bafs relieves. Indeed there is nothing more required than to form a mold by laying them on a proper board ; and, having furrounded them by a rim made of a piece of a card or any other pafteboard, to fill the rim with foft tempered plafter of Paris : which mold, when dry, will ferve for lèverai cafts. It is neverthelels a better method to form the mold of melted fulphur ; which will produce a {harper impreflion in the cad, and be more durable, than thofe made of plafter.
The cafts of medals are likewife frequently made of fulphur : which being melted, muft be treated exa&ly in the lame manner as the plafter.
Cafts may be made, likewife, with iron with very little additional trouble, provided it be prepared in the following manner.
“ Take any iron bar, or piece of a fimilar “ form; and, having heated it red hot, hold it “ over a veflel containing water ; and touch “ it very {lightly with a roll of fulphur : which “ will immediately diftblve it ; and make it “ fall in drops into the water under it. As “ much iron as may be wanted being thus dif- “ lolvcd, pour the water-then out of the vef- “ fel ; and pick out the drops formed by the “ melted iron from thofe of the fulphur, “ which contain little or no iron, and will be ‘^diftinguifhable from the other by their co- • “ lour and weight.”
The iron will, by this means, be rendered lb fufible, or eafy to be melted, that it will run with lefs heat than will melt lead; and may be employed for making call of medals; and many other fuch purpofes, with great convenience and advantage.
Impreffions of medals, having the lame effeét as cads, may be made alfo of ilinglafs glue by the following means. Melt the ifin- glafs, beaten as when commonly uled, in an earthen pipkin, with the addition of as much water as will cover it, ftirring it gently till the whole be diliolved. Then, with a brulh of camels hair, cover the medal; which Ihould be previoully well cleanfed and warmed, and then laid horizontal on a board or table greafed in the part around the medal. Let them reft afterwards till the glue be properly hardned ; and then, with a pin, raife the edge of it; and feparate it carefully from the medal ; the caft will be thus formed by the glue as hard as horn; and fo light, that a thoufand will fcarce- ly weigh an ounce. In order to render the reliëf of the medal more apparent, a fmallquan- . tity of carmine may be mixed with the melted ilinglafs; or the medal may be previoully coated, with leaf gold by breathing on it, and then laying it on the leaf, which will by that means adhere to it : but the ufe of the leaf gold is apt to impair a little die lharpnefs of the im- preflion.
There is likewife a method of making impreffions of the fame kind in lead : which is this.
Lay the medal on a poft, or other firm body of wood; and cover it with a piece of very thinplateoflead; and layoverthatanother piece of thicker plate. Then place on them endways, a piece of wood turned of a round figure; which may be a foot or more in length j and of fitch thicknefs, that its diameter may be fome- what greater than that of the medal. Strike then forcibly on the upper end of the wood with a mallet, or fbme iuch inftrument; and Ac undermoft plate of lead will receive the imprefiion of the medal: to preferve which, the concave of the reverfe may be filled up with refin, mixed with an equal part of brick- duft, and melted. The imprefiion fhould be made with one ftroke j which will produce a fufficient effe<3:, if given with due ftrength, and in a perpendicular direftion. Impreflions may be even taken from fealing wax or fulphur in this manner, if the pieces be no way concave or bending on their under fide.
Impreflions of medals may be likewife taken in putty j but it fhould be the true kind made of eartn of tin and drying oil. Thefc may be formed in the molds previoufly taken in plafter or fulphur, or molds may be made in its own fubftance, in the manner directed for thofe of the plafter. Thefe impreflions will be very fharp and hard: but the greateft difadvan- tage, that attends them, is' their drying very flowly, and being liable in the mean time to be damaged.
Impreffions of prints, or other engravings, may be taken bom copper plates by cleaning them thoroughly; and pouring plafter upon them: but the effect, in this way, is not ftrong enough for the eye: and therefore the following method is preferable, where fuch impreffions on plafter are defired.
Take vermilion, or any other coloured pigment, finely powdered, and rub it over the plate. Then pais a folded piece of paper, or the flat part of the hand, over the plate to take off the colour from the lights or parts where there is no engraving. The proceeding muft then be the lame, as where no colour is ufed. This laft method is alfo applicable to the making im- preflions of copper plates on paper with dry colours : for the plate being prepared as here directed, and laid on the paper properly moift- ned, and either pafied under the rolling preis, or any other way ftrongly forced down on the paper, an impreffion of the engraving will be obtained.
Impreffions may be likewife taken from copper plates, either on plafter or paper, by means of the fmoke of a candle or lamp; if, inftead of rubbing them with any colour, the plate be held over the candle or lamp, till the whole furface become black, and then wiped off by the flat of the hand, or paper.
Thefe methods are not, however, of very greaf ufe in the cafe of copper plates j except where impreffions may be defired on occafions where printing ink cannot be procured: but as they may be applied likcwife to the taking impreflions from fhuff-boxes, or other in- graved fubjeCts, by which means defigns may be inftantly borrowed by artifts or curious pcr- <bns, and preferved for any ufe, they may in fuch inftanccs be very ufeful.
The expedient of taking impreflions by the iinoke of a candle or lamp may be employed, alfo, for botanical purpofes in the cafe of leaves; as a perfect and durable reprefentation of not only the general figure, but the contexture and (fifpofition of die larger fibres, may be extemporaneouily obtained at any time. The lame may be, neverthelefs, done, in a more perfect manner, by the ufe of linfeed oil, either alone, or mixed with a fmall proportion of colour, where the oil can be conveniently procured: but the other method is valuable on account of its being practicable at almoft all feafons, and in all places, within the time that the leaves will keep frefh and plump. In taking thefe impreflions, it is proper to bruife the leaves, lb as to take off the projections of the large ribs, which might prevent the other parts from plying to the paper.
Leaves, or allb the petals, or flower leaves of plants, may themfelves be preferved on paper, with their original appearance, for a con- fiderable length of time, by the following means. Take a piece of paper, and rub it over with the ifinglafs glue treated as above directed for taking impreflions from medals; and then lay the leaves in a proper pofition on the paper. The glue laid on the paper being fet, brufh over the leaves with more of the fame ; and that being dry likewife, the operation will be finifhed : and the leaves lo fecured from the air and moifture, that they will retain their figure and colour much longer than by any other treatment.
Butter flies, or other fmall animals of a fiat figure, may alio be preferved in the fame manner. .