There are few of the artistic crafts more fascinating than enamelling, and certainly none more beautiful. To enter into the work seriously a muffle furnace is required, but small pieces of work in both Cloisonne and "Limoges" may be done in a crucible, with a large blowpipe or in a large methylated-spirit flame. Small articles of jewellery may easily be enamelled, and a considerable insight into the work may be gained with a comparatively inexpensive outfit.
The process consists of coating the surface of copper, silver or gold with a layer of melted glass. The glass is made from silica, red-lead and potash, either carbonate or nitrate, and in various proportions, which form, when in combination, which is produced by melting in a crucible, a flux. The flux is transparent and colorless, capable of adhering to either of the above metals without cracking after it has been fused or melted. The coloring is done by the addition of various oxides of metal and made opaque by means of tin or lead. The principal oxides used are those obtained from gold, copper, iron, cobalt, manganese and antimony, the gold oxide giving ruby; copper, both green and turquoise blue; iron, brown and orange; cobalt, ultramarine blue; manganese, purple; and antimony, yellow. It is possible to mix them together, and they will combine similar to water colors. Enamels require a long heating, anything from five to thirty hours continuous melting; the harder enamels being those which require the greatest heat to melt and which are certainly the best to use, although it is very convenient to have a soft enamel, which will melt or "run" at a fairly low temperature.
The different methods of using enamel are as follows:-Cloisonne; Champleve, Plique-a-jour, Bassitaille and Limoges or painted enamel. The first process on the list will be found most useful for general purposes, and will be very fully described. It may be considered as a method of filling up small spaces made on a piece of metal by means of narrow strips, with enamel ground to a fine sand, and then fused in a furnace crucible, or in a spirit flame, according to size, the amount of heat required depending on the hardness or softness of the enamel used. The metal strips of rectangular wire are called "Cloisons," hence the name cloisonne, and the enamel is usually opaque; these cloisons are not necessary to hold the enamel together, but should be used to form the design, for the enamel adheres quite as well without the cloisons as with them. Champleve-enamelling consists in carving out of a thick piece of metal different spaces which will form a design, leaving the edges of the spaces to form the outline, if necessary, of the ornament. Into these spaces, opaque, or sometimes transparant enamels are run, which form the design. The work requires great skill in cutting out the spaces and the best metals to use, either bronze or very hard brass. It will be noticed that both the above processes are similar, the difference being mainly in the method of making the spaces which, in cloisonne are built up with soldered walls of thin metal, and in Champleve are sunk below the surface, the metal itself forming the divisions.
The method of applying the enamel and firing it being the same in both cases, there will be no need to treat them separately. The next process, that of Plique-a-jour, is somewhat similar to thee above, but without a back, and is really a method of enamelling the spaces between a network (as the word means) of gold, silver or copper wire, and it may be considered as cloisonne without the necessity of keeping the ne-amel in place while it is being fused, the method being to place the work vertically in a very fierce mulfle. The work may consist of soldered pieces of wire forming a suitable design, or as is more often the case, the spaces are cut away with the fretsaw, and the divisions left in the metal itself. Very beautiful effects can be gained by this process, which is very fairly light and delicate, and it is well worthy of a trial. The next process, Bassitaille, is not a commonly-practised method, mainly on account of the great artistic skill and technical knowledge required. The word means "low cut," and the effect is gained by carving out the design, sunk below the level of the metal usually, in low relief, or in repousse, in high or low relief, and then the metal is entirely covered, both sides, with transparent enamel or enamels, allowing the details of the carving to show through the enamel. It is a very beautiful process, but as it is usually in gold, and is seen to its greatest advantage with that metal, it will be found rather too expensive for ordinary art workers.
The remaining process to be described is "Limoges" or painted enamel, so called because it was first practised at Limoges, about the end of the fifteenth century, and the enamelling is done in the simplest and most straightforward manner, compared with the difficult and tedious preparation of the metal in the methods described above. Very small articles of jewellery may be made by this process, but it is in the painted panels of some few inches in area that the finest work is seen. The enamel is ground down to a fine powder, mixed into the consistency of paint, and then used much in the same way as water colors, the work being somewhat limited, but making up in depth of color what it lacks in tints. The subject is painted on a domed plate of copper, which is covered with a ground of enamel, black, blue or some suitable color. Upon this ground the painting is done in semi-transparent white enamel, known as grisaille. The grisaille is fired, other enamels of various colors are painted over and again fired.
To make satisfactory Limoges enamels, considerable practice in enamelling is necessary as well as artistic taste and skill. Of all the above processes, those most useful to the artworker who wishes to make jewellery are Cloisonne, Chempleve and Limoges, the others being left with advantagee until the easier methods have been practised.
We shall therefore describe these three processes in turn, for the reasons which we have given, commenc ing with the more simple methods of work, and Cloisonne being perhaps the most useful of the three, will be the best to begin with. The first thing to be considered is, or course, the enamels, and they are purchased in all colors similar in form to lumps of glass.
It is quite necessary to know how to prepare the enamels, so the process will be described. The required piece of enamel is taken and pounded up into small pieces, in a mortar, with a pestle having a wooden handle (Fig. 1). a Wedgewood No. 3 size costing about 2s. 3d., or a porcelain of the same size only Is. 6d.
A wooden mallet will be necessary in beating the pestle to thoroughly pulverise the glass, but of course great care will be needed that the side of the mortar is not broken. The pestle should be held directly over the pieces of enamel, and the blow given exactly on the head of the pestle. As soon as the enamel has been reduced to a coarse grit, it should be further reduced, and this is done by grinding it to a fine sand; the pestle is held firmly in the right hand, and holding the mortar in the left, rotate the pestle until it is sufficiently ground. Considerable pressure is required, and a contrivance similar to that shown in Fig. 2 will be found very useful in easing the work. A long iron rod should be fitted either into the top of the pestle, and a bracket fixed either to the wall or to the bench, and through the top should be passed the other end of the rod; lead weights may be placed on the rod resting on the top of pestle, and any pressure almost may be exerted on the pestle. It will be seen that the water becomes cloudy as the grinding progresses, so that the enamel should be washed, if it is transparent, but not if opaque, and the washing is done by agitating the sand while in the mortar, and continually changing the water. The fluid may be poured into jars and allowed to settle, the residue being used for backing the plates, for the enamel is useless for anything else, being opaque and cloudy.
For Limoges work the enamel will have to be ground to a powder in an agate mortar (Fig. 3), but this will be rather expensive, for the smallest agate mortar, with pestle, costs $1.00, and is only 2 inches in diameter, and the larger sizes about 4 inches, costing $5.00 or so. It is quite necessary, if really good work is to be done, to invest in this piece of apparatus, for the trace of foreign matter will spoil an otherwise good enamel.
It is much better to use enamels as soon as they are ground, but if this is not possible, then keep them in jars under water and then not more than a week or so, or else in bottles securely corked. If the powdered enamel is old, or has been exposed to the air, it will become disintegrated, but where it is necessary to use it, it should be washed for a few minutes with weak hydrofluoric acid, about 1 part to 12 parts of water, and then, after washing away all trace of the acid, it may be used. Great care must be taken in using this acid, as its fumes are highly poisonous.