CASTING IN PLASTER.
Modelling and taking casts are kindred employments, as by means of the latter process a panel or statuette can be repeated indefinitely with comparatively little expenditure of time or labor. The process is purely mechanical, and can be mastered by any one who is willing to devote the necessary time and patience to it. Casts are made either in plaster of Paris or gelatine. The process is twofold, the first step being to make a mould from which the cast is afterwards taken.
To do this fill a pan or basin half-full of water, and pour gradually into this enough plaster to absorb the water. Then stir with a spoon for a minute or two until you have it about the consistency of thin cream. In this state it is called "slip." This "slip" when poured over a surface to the depth of an inch or two will adapt itself to every inequality of surface while in a liquid state, but will rapidly harden. If, after hardening, it is removed, it will present a reversed copy of the surface over which it has been poured.
Plaster of Paris plaques, for instance, can be readily made by pouring "slip" into a plate or plaque which has been thoroughly oiled. Liquid gum arabic and dissolved alum added to the "slip" will render it extremely hard and durable. A plaque thus made can be painted.
In order to take a cast of a bas-relief in clay build a wall of clay around the object to be cast, making it two or three inches high, or, if preferred, a cardboard box exactly fitting it may be used. Oil your model, which must be thoroughly dry, with boiled linseed oil, using a brush to put it on with. Wipe off any superfluous oil, and pour in the "slip" to the required thickness, shaking or gently striking the mould to make sure that the plaster settles into every crevice. In about ten minutes the cast, though still damp, will be firm. Remove the clay wall or the cardboard box, and cut away the edges until you can see the line of separation between the plaster and the clay. Separate them carefully, aiding the process with a dull kitchen knife. It will take about twenty-four hours for the plaster to become thoroughly hard.
The next cast must be taken in the same way, except that the plaster cast just taken is to be used as a mould. The resulting cast, if carefully managed, will be a facsimile of the clay mould. When the "slip" is mixed with gum arabic and alum solution, as directed above, such a cast is durable enough to be used as a panel in a bracket or cabinet.
Fine casts of wood carving or solid leather work can be taken in this way, and if dyed with lamp black, umber, and beer, will be very good imitations of oak.
The slip can be tinted with any desired color by mixing any dissoluble color in the water used for making the slip. In bas-reliefs a fine effect may be obtained by pouring white slip into the sunken portions of the plaster mould, and then filling the mould with slip tinted to a delicate shade of blue. When taken from the mould the design should appear white on a blue ground.
Casts can also be made to imitate ivory by either using milk and water for the slip, or by oiling the completed cast with oil in which a little beeswax has been dissolved. When dry rub with cotton wool, and keep in a smoky room for a while.Gelatine moulding is done in the same way as moulding in plaster, the gelatine being dissolved in cold water. If to the water is added a very small proportion of tannic acid (Mr. Leland says a "few hundredths"), the cast will be almost impervious to water. Gelatine is a much cleaner material to handle than plaster, and rather easier to manage. The best is the French, and can be obtained at stores that supply materials for carvers and gilders.
The directions given above are for flat objects, but when a cast from the "round" is to be taken the process becomes more tedious and complicated. An egg is one of the simplest "round" objects to cast, and the process of moulding one of these will illustrate the process to be followed generally.
Have a pan or dish of sand, and place the egg in it so that one half will be above the sand. Pour the slip carefully over this until it is covered to the requisite thickness. Having the mould of one half of the egg, replace the egg in it, oil the edges of the mould, having dug out little holes at intervals to receive corresponding projections on the other half of the mould. Cover the other half of the egg with slip. When this second half is dry oil the inside of both halves, fasten them together by means of the holes and projections spoken of, and through a small hole prepared for the purpose pour in slip, shaking the mould gently until the plaster has hardened.
Some objects have to be cast in moulds of three or more pieces. Sometimes these are separated by means of fine strings passed carefully around the mould, the ends coming through. Sometimes a dull knife is used for this purpose, and sometimes the different parts of the mould are obtained by successive casts, as was done in getting the two parts of the egg.
Fruits can be very successfully imitated by using wax for making the casts from plaster moulds made as described above. To save expense, however, most fruits are cast hollow, which is effected as follows:—
Soak the two pieces of the mould in hot water. The wax should in the meantime be very slowly melted in a tin saucepan with a spout to it, care being taken not to let. it come to a boil, or it will be discolored. A lump the size of the object to be imitated, should, as a rule, make two casts.
As soon as the wax is melted thoroughly, place the saucepan on the stove, and taking the parts of the mould from the hot water, remove the moisture from their surfaces by pressing them gently with a handkerchief or soft cloth. Use a very light hand, merely pressing but not wiping the mould. Perform this drying process quickly, or the mould will be too cool, congealing the wax too rapidly:, and causing it to settle into ridges; on the other hand, the wax must not be too hot, or it will adhere to the mould, and will not come out entire.
Having laid the two halves of the mould so that there can be no mistake in fitting the one to its exact place on the other quickly, pour from the saucepan into one of the half moulds nearly as much wax as will fill the hollow made by the model, quickly fit the other half on top of it, squeeze the two pieces tightly together in the hand, and still holding them thus, turn them over in every possible direction, so that the wax which is slowly congealing in the internal hollow of the mould may be of equal thickness in all parts. Having continued this process at least two minutes, the hands (still holding and turning the mould) may be immersed in cold water to accelerate the cooling process. The perfect congealment of the wax may be known after a little experience by the absence of the sound of fluid in shaking the mould.
As soon as the mould is completely cooled, the halves may be separated carefully, the upper being lifted straight up from the under, and if the operation has been properly managed, a waxen fac-simile of the model (so far as shape is concerned), will be turned out of the mould.
This, however, will require trimming, so as to remove the ridge which marks the juncture of the two halves of the mould, and any scratches or inequalities make by the knife in removing the mould should be polished out with a piece of soft rag, wet with spirits of turpentine or wine.
The wax may be tinted by stirring into it while still on the stove a little of the required color. The tube colors used by artists are preferable. When required of a very delicate tint, as for the green gooseberry, the color may be thinned by the addition of a little Canada balsam and spirits of wine. The shading and varied coloring must be added after the fruit is cast.
Some of the smaller fruits, such as the raspberry, mulberry, etc., are cast solid. In this case a hole must be made through the mould at a point corresponding to that at which the stalk is to be inserted. Afterwards the stalks are added before the wax is poured in.
The stalks of fruit are usually made, like those for wax flowers, of wire covered with silk, except in fruits having a very large stem, like the cucumber, when a roll of green silk or cotton, stiffened by a wire through the centre, should be laid on the groove of the mould. It is well to allow the cotton or silk to project into the body of the fruit at least half an inch, so that when the casting is complete, the stalk will be firm in its place and will bear the weight of the fruit.
Wax flowers are made from sheet wax which can be bought prepared and tinted for the purpose. For the benefit of those who may wish to try preparing the sheets themselves, I give the following directions, said to be reliable:—
To every pound of wax we have added about an ounce of Canada balsam, or spirits of turpentine, or of a solution of resin in spirits of turpentine. I think the last named is best for colored wax, but the first or second for a white wax. If the wax is frequently melted, it will require a little turpentine added to it. A composition of this kind having been melted in a glue pot, or in any other vessel which will not allow the contents to be overheated, should be poured into oblong tin moulds about two inches deep, two inches and a half wide, and four inches long. These can be made by any tinman; the edges should be turned down at the top and strengthened with wire as with common bread tins. This tin should not be filled quite full, and the wax should be allowed to cool slowly, or it will wrinkle and require re-melting. Slow melting and slow cooling are essential points. When completely cold, the wax will separate from the tin by its own contraction, and may be shaken out by tapping on the bottom of the mould. You have now a Mock of wax which it is required to make into thin sheets, and this is accomplished in the following manner: Obtain a carpenter's spoke-shave, which is flat, and the Made of which is at least an inch broader than your block of wax. In order to prevent the block of wax from slipping while the shaving is going on, the following plan has proved successful. Have a hard piece of wood cut in the shape of a capital T. The cross piece should be the width of the block of wax, and the leg should be about three inches long. This leg must be inserted in a square hole in the table on which you intend shaving. A plug can be made to fit into it when the hole would be inconvenient. When shaving the block of wax, the top of the cross piece of the T should be kept as near the upper edge of the wax as will allow the spoke shave to pass easily over it. The shave must be well warmed at the fire or by dipping it into hot water. If you have two shaves you can warm one, while using the other. The cutting stroke should be made steadily but quickly. The thickness of the sheet must depend on the adaptation of the shave, which must be learned at the time of purchase. The first three or four sheets will not cut equally, but the wax will remelt; the most perfect sheets only should be laid aside for use. For preserving them in nice condition, lay them between sheets of paper which have been brushed over with boiled linseed oil, and which have been allowed to dry. The wax may be tinted as directed above by using the following colors in different proportions: chrome yellow, Prussian blue, French ultramarine, carmine, and flake or Chinese white.
Wax flowers are or should be modelled after real ones rather than after patterns cut in tin or cardboard, and to enable one to do it well several of the flowers to be copied should be kept at hand. Pick one carefully to pieces, and cut petals, calyx, etc., carefully out, curling and moulding them over a long pin. Put them together as far as possible in imitation of the way in which they grow. The stems are made as directed for fruit, over fine wire. Very fine wire may sometimes be used as the foundation for stamens and pistils. Begin with very simple flowers, and copy Nature as far as possible. Autumn leaves are one of the easiest things to imitate, and are good practice for coloring. As said before, where practicable, tinted wax is used to give the local color, but this must be shaded and variegated after the petals, etc., are cut out. Water colors in powder are used for this purpose, and are applied in the following manner:
Having taken a very minute quantity of color powder on the blade of a penknife, lay it upon a palette, or the under side of a plate, and press it with the blade to destroy any lumps. With the penknife also add a very small quantity of weak gum-water, and work the mass to the consistency of cream. The colors must be applied with pointed tinting brushes. Each color requires a separate brush, as powder color will not mix like fluid ones. The brush must be held upright at right angles to the wax, and the color applied in the direction of the graining. The color must be applied at once.
The flower end of the apple and many other fruits can be imitated by pushing a clove into the eye of the fruit. Highly glossy fruit may be varnished with mastic. The down upon peaches, etc., may be imitated best with the flock used by paper-stainers. The fruit having been varnished or wet with spirits of turpentine, should be rolled in the flock or bran, the latter blown on it. The bloom upon plums and grapes is imitated by dusting them with common powder blue.
When wax-flower making has to be done choose a warm situation for your work. If the hands are too hot and the wax is thereby rendered too flaccid, wash in tepid water. The hands are oftener too cold; in which case washing in hot water and a seat near the fire are recommended. Never be in a hurry, or you will spoil your flower. Be careful in cutting the petals, etc., correctly. After having dissected and imitated a flower preserve patterns and sketches of its different parts, so that when the season for the plant has passed other copies of it may be made. Always hold the flower in the left hand, and apply fresh pieces with the right. Coarse silk dipped in wax may be used for fine stamens. The tips dipped in flour and then coated with wax will imitate anthers very well.