Process: When you have decided upon the colour which you wish, put as much enamel as you will need into the mortar and cover it with clear water. The water washes the enamel and prevents it from flying out as it is broken up. Place the pestle on the pieces of enamel and tap gently upon the end of the pestle with the wooden mallet, till the enamel is broken up into fine pieces. While doing this the water will become discoloured. Drain the water off and pour fresh water on. Repeat this so long as the water becomes discoloured. With the pestle grind the enamel to a fine paste. Press down upon the pestle, at the same time give it a twisting movement with the wrist. When the water remains clear and the enamel is pasty and free from lumps it is ready for use. While using it keep it just covered with clear water. This prevents its drying and in this dampened state it is in the best working condition.
How to place the enamel on the metal: With the small spoon pick the enamel up out of the mortar, place it on the metal and press it down into any depression. Keep it well moistened all the time. Repeat this until the whole depression is covered. If any part is left uncovered, that part will show black after firing. Then each black spot must be scraped clean, covered with enamel again and refired, which makes much unnecessary work, so be careful at the first to place the enamel just where it should be on the metal, and so avoid the extra work and firing. The muffle furnace: This is a small furnace made for the purpose of melting enamels by what is called a reflected heat. The muffle is a half rounded, shaped clay form open only at one end, into which the piece to be fired is put. The flame of the furnace plays on the outside of this muffle. The temperature is raised to the required heat and the piece inside the muffle is fired without having any flame playing directly upon it. The reflected heat does the work. These furnaces can be bought in almost any general supply store. They come in all sizes. Natural or artificial gas can be used for heating; the regular hose or tube attachment is all that is necessary.
The piece in place for firing: It is usually best to light the oven before you begin to place the enamel on the work to be fired. The furnace heats up in the meantime. Place the piece on the top ledge of the furnace close to the chimney. This is a good place to dry the moisture out of the enamel. If this is not done the steam generated by the moisture and the heat causes explosions, which in turn disturb the enamel surface and dislodge small particles of the enamel. When the steam has stopped rising from the enamel—which you can tell by holding the piece between you and the light—the moisture has dried out and the work can be put into the muffle by use of a long pair of muffle tongs. Extreme care must be taken when placing the piece to be fired into the furnace. The enamel is now very dry. The particles are no longer held together by the moisture and the least jar will dislodge them. The doors of the furnace are usually in two pieces, so that the upper half can be lifted away from time to time. One can look in and watch the process of melting. When the enamel is first put into the furnace and the heat begins to melt it, it rapidly changes colour. As it begins to melt it settles down and takes on a glassy, soft, smooth surface. At this point it is ready to take out. It is placed again on the top of this furnace, where it cools off slowly, otherwise the difference in expansion between the metal and the glass would cause the surface to crack. After one or two trials one easily recognizes the critical time when the enamel is well baked. These directions are only for enamelling flat surfaces. If one should wish to enamel both the inside and outside of a box lid rounded on the top and curved on the under side, a few large drops of gum arabic should be mixed with the enamel used for the under side. This prevents it from dropping off when in position for firing.
When the work has cooled off so that it can be handled, it will show a surface every part of which is covered, if carefully done. If not the black spots will appear. These are copper spots oxidized by the heat, and must be thoroughly scrubbed and scraped. The enamel edges around these spots must be scraped away, covered with enamel, and refired. If there are no spots shown, the work is ready for finishing. You will find on the upper edge of the enamel line a black line caused by the impurities in the enamel which rise to the top edge. Scrape this off with a fine file until it entirely disappears.
The copper, too, usually takes on beautiful colours during the heating process. Many like to leave the colours just as they happen to come by the heat, others prefer to polish the surface to bring out the real copper colours rather than the oxide colours. To clean the oxide off one must put the piece into a pickling bath made up of one part of sulphuric acid to eight parts of water. This softens the scum on the surface of the metal so that a soft rag dipped into any cleaning material like pumice stone will easily clean it off.
TWO METHODS OF ENAMELLING
Cloisonné: In this work the design is done usually in coloured enamels, which are separated one from another by means of ribs of metal bent so as to follow the outlines of the design. These ribs are placed on the plaque, and a drop of solder here and there keeps them in place. The coloured enamels are filled in between these ribs and fired as before explained.
Champlevé: In this method the partitions between one colour and another are formed by ridges of the base and not by separated ribs of metal. These ridges are made by driving the metal with chasing tools from the under side up and raising it above the surface. The spaces between these walls are filled in with enamel, and it is all fired as explained before.
The lid on the rose jar as shown in the group is an example of this kind of enamelling.