A Select Collection of Valuable and Curious Arts and Interesting Experiments, / Which are Well Explained and Warranted Genuine and may be Performed Easily, Safely, and at Little Expense.

by Unknown

65. Best cement for joining china or crockery.—Heat a piece of chalk to a full red heat in a fire; and while this is heating, take the white of an egg, and mix and beat together with it, one fourth of its weight of pondered or scraped cheese, (such as is most void of cream, or oily matter is preferable) or the curd that is formed by adding vinegar to skimmed milk;—take the chalk from the fire, and before it is cold, reduce it to powder, and add as much of it to the mixture as will form a thick paste, and beat them anew all together, and use the composition immediately. When this is dry, it will resist, in a great measure, either heat or moisture. A semi-transparent cement, suitable for china ware, may be made by gently boiling the flour of rice with water.

66. To make a strong water proof glue.—Dissolve common glue in water in the usual way, and dip into it some clean paper, sufficient to take up an ounce or more of the glue. When the paper is nearly dry, roll it up, or cut it into strips and put them into a wide mouthed phial or flask, with about four ounces of alcohol; suspend this over a fire so as to boil it gently for an hour, having the cork set in slightly to prevent its taking fire, but not so as to prevent the vapour entirely. Then take out the paper (the only use of which is to give the glue more surface for the action of the alcohol) and add one ounce of gum-shellac in powder; continue the heat, often shaking the mixture till the shellac is dissolved. Then evaporate it to the proper consistence for use. Note.—Many experiments have been made, in order to discover some aqueous size, that when dry, would resist moisture: and some have recommended skimmed milk, and others vinegar as a menstruum for the glue. But it does not appear from trial, that either of these are but very little better for this purpose than water; nor is it probable that any similar composition of size will resist moisture much better than common glue, especially if it be mixed with sulphate of lime, or some similar substance by way of support.

67. The art of moulding figures in relief.—Mix together and temper with a solution of gum-arabic in water, one part of clean, sifted wood-ashes, and two parts of fine sulphate of lime. Knead this composition on a board, till it has the consistence of putty. Press a ball of this putty on any medal, coin or carved work in relief, (which must be previously oiled) and let it dry; then take off the mould thus formed, and oil the part that has received the impression of the figure, with olive oil;—make a small orifice through the mould, from the centre, or deepest part of the impression; also, pare off the border of the mould, to within half an inch of the impressed figure. Then lay a small piece of the putty on the board and press the mould down hard upon it, that it may not only fill the mould, but that the redundant part may be pressed out beyond the border of the mould: raise the mould a little and blow through the orifice, to detach the new moulded figure from the mould. Thus any number of figures may be readily produced, suitable for ornamenting chimney pieces, or mouldings, and which will be very hard when dry, and may be painted with any coloured oil paints, which will also preserve them from moisture.

68. To cast images in plaster.—For this purpose a model of the figure that is to be cast, must be provided, and suspended by a rod or staff, one inch in diameter, and fixed in the top of the head. This model may be made of wood, chalk, or any other substance that is smooth, and sufficiently cohesive to support itself. This being prepared, mix fine sulphate of lime with water, to the consistence of soft putty, and having brushed some olive oil over the model, cover it completely with the plaster, which must be applied, and spread over it with the hands, to the depth of two inches or more. When the plaster is nearly dry, divide it into several parts with a thin blade, so as to take it off from the model without breaking any part. When the several parts of the mould are dry, oil them inside and put them together as before, and bind them with pieces of tape or twine; set the mould upright, and fill it with a fresh mixture of sulphate of lime and water, of as much consistence as may be poured in through the aperture at the head. This plaster should be poured into the mould as quick as possible after being mixed; otherwise it would become too stiff, and be spoiled. The plaster in the mould will soon cohere, so that the mould may be taken off, and the figures may be set up to dry; and the mould being oiled and put together again, is ready for another cast.

69. To produce embossed letters, or figures on marble.—Take some of the coloured varnish described at 37, and with a hair pencil, draw the letters, &c. on the marble, (which should be previously well polished,) and also cover with the varnish, every part of the face of the marble that is to remain plain. Lay the marble in a horizontal position and make a border of oil putty round it, and pour on muriatic acid to the depth of half an inch on the marble. When ebulition ceases, the acid may be drained off, and the work examined; and if the letters are not sufficiently prominent, a fresh quantity of the acid may be added. When the work has been thus corroded to the depth required, the varnish may be washed off with spirits of turpentine. The acid that has been thus employed need not be lost, for a muriate of lime being thus formed, may be crystallized by a slight evaporation, and preserved for other purposes; or by the addition of a small quantity of sulphuric acid a sulphate of lime is precipitated, and the muriatic may be poured off and be used again for the same or a similar purpose.