From copper, bronze, or other metals, gutta-percha moulds may be taken. They are durable, elastic, and easily managed. The gutta-percha must be boiled; then it is so soft that it can be moulded into any shape, and can be pressed and worked on to the face of a medal so as to secure the minutest impression ; but it must be allowed to get quite cold and hard before it is removed.

For low relief and medals of delicate tracery, wax or paraffin is a good substance to take impressions in.

Ordinary white wax, or paraffin - the ends of candles will do - must be melted carefully, and must be kept very clean, and when melted the process to be followed is exactly the same as that for the sulphur process. Remember that wax is very slow in cooling.

To take copies of solid objects, like the cast of a head, or of an animal, or a vase, the mould must be taken in pieces, so that when tied together the inside mould is an exact counterpart of the object. This requires a little more skill than that for taking the flat medal, but undoubtedly some of our readers will have ingenuity and perseverance enough to attempt it. If you wish to go in for it, we should advise you to call in at an image-makers, and he will always show you such a mould, and at once you will be able to see how the parts are cast and held together better than any such short description as our space will allow us to give.

If you wish for a polish on the surface of your medals, you can secure it by the following method.

Get some good white curd soap; cat it into fine shavings with a clean sharp knife; then make it into a strong solution. Immerse the face of the medal or whatever is to be polished in it several times, bat let it dry between each dip. It will then take a good polish on being rubbed briskly and lightly by means of a piece of cottonwool It will also have the smoothness and whiteness of marble. If yon wish to paint them you can do so; or you can bronze them by covering them with a thin coat of gold size, then sprinkle them over with bronze powder, which you can get of any colourman. Bas-reliefs can be cast in the manner we have described, and may be put together so as to form pedestals for ornaments. Brackets may also be made in plaster, taking castings from real fruit and leaves. In taking a cast of fruit or solid object, it must be partially buried in fine white sand just sufficiently moistened to hold it together; then a frame of cardboard can be put round the projecting part, and a cast taken. When the plaster is set, the portion of the fruit that was buried can be cast in the same manner, well oiling the edge of the mould first taken, so that the second portion may easily separate from it.

To take the most durable copies of medals is however to take electrotypes of them. This is done by quite a different process; but it is so interesting as well as useful that we will describe it here. This brings us into the subject of electricity, which most of our readers in these days will know sufficiently about so as to be able to understand the following simple instructions.

The process is called electrotyping, and it depends on the decomposition of a substance called sulphate of copper.

A very simple apparatus for copying medals you can make for yourselves. It is shown in Fig. 139. It consists of a lamp-glass (a), the lower end of which is covered with a piece of bladder (b), which must be tied so securely that when the vessel is filled with a liquid it does not run out. This may be replaced by a porous pot, such as is used in a Daniell's battery if you prefer it, and it is better. The outer vessel can be a jar or a basin (c), or any vessel that will allow you to carry out the following arrangements. The stand (s), as shown, can be made of two upright pieces of wood and a cross-piece at the top. Now you must have a strong solution of sulphate of copper, sold under the name of blue vitriol or blue-stone. This you put into the outer vessel. The inner vessel must have a solution of sulphuric acid and water, about twelve parts of the latter to one of the former. In this a zinc rod (z), covered with quicksilver, must be fastened either by solder, binding-screw, or by a tight twist to a length of copper wire, This may be wound round the cross-piece at the top so it acts as a support, and then turned downwards, as shown in Fig. 139, and then again at right angles, to which the mould of the medal (m) is fastened. The mould can be taken in gutta-percha or wax, but the face must be covered with a thin layer of blacklead, and the wire carrying it must also be in touch with it, so as to form a continuous conductor. The hollow of the mould must have its face towards the bottom of the inner vessel. To set the whole going, the zinc rod is immersed in acid and water, the wire forming a good connection with it and the mould which is immersed in the solution of sulphate of copper. An electric action will be set up, and copper thrown down from the sulphate of copper solution. In the course of about forty-eight hours sufficient copper will be deposited in the mould as to admit of its being taken off. This copper will be pure, and having been thrown down in tiny particles, it will give an exact counterpart of the mould into which it is deposited. The copper solution must be kept up at the same strength, or it will be better to tie a few crystals into a muslin bag and hang them inside the basin. Then as fast as the copper is taken out of the solution by deposition, so fast will it be taken up from the bag of crystals.

Fig. 139. - Simple arrangement for Electrotyping.

In this case the electricity passes through the liquid from the zinc to the mould, decomposing the er sulphate, and depositing the copper.

This is such a delicate method of taking an impression, that even a photograph can be copied. It is also very useful for taking copper-plate engravings. In another chapter we will give you instructions for making a more complete apparatus for this purpose.