Copper Work Part 7

[Ill.u.s.tration: FIGURE 34.]

In the fourth method the design is transferred to either side of the object. After placing it on a pitch block, depressions may be made from the face or lines raised from the under side.

After the part.i.tions have been formed, the object must be thoroughly cleaned and brightened by dipping in a bath of nitric acid. After dipping, which should be done quickly on account of the rapid action of the acid on the metal, it should be rinsed thoroughly in clean water.

This process removes all dirt and leaves the metal bright. After this cleaning, the fingers should not touch any part of the object that is to receive the enamel.

To prepare the enamel for application it must be ground. First break it into small pieces with a hammer. To keep it from flying about, it is well to roll it up in a piece of heavy wrapping paper. It is then placed in a porcelain mortar and, with a little water and a pestle, it is ground about as fine as fine sand. The water is poured off and the enamel rinsed several times in clean water until the milky substance disappears. Unsatisfactory results often come from lack of care in was.h.i.+ng the enamel. After was.h.i.+ng it is removed from the mortar to a small saucer by the use of a palette knife. While still wet, which allows its being spread more easily, the enamel is applied to the object with a soft hair brush.

All of the enameling suggested in this book may be done with an ordinary blow-pipe or a Bunsen burner, but more satisfactory results are obtained with a kiln.

[Ill.u.s.tration: FIGURE 35.]

To apply the process to a definite piece of work, the steps necessary in enameling the Stamp Box cover on Plate 24, No. 3, will be taken up. It will be a.s.sumed that the box is made, ready for the application of the design as shown on the plate. The design is first transferred to the cover and then cut away. It is cleaned with kerosene and dipped in nitric acid as before explained. After being thoroughly washed, it is ready for the enamel. In applying the enamel care must be taken not to get particles outside of the channels. After the moisture has evaporated and the enamel has been fired it settles considerably so that this must be allowed for by rounding it above the surface. After the enamel has been applied, the strip that is soldered to the under side of the cover must be protected from the heat before firing, as the temperature required for fusing the enamel is several times greater than that required for soldering. The soldering is protected by placing a paste made of yellow ochre and water about the soldered joint both inside and outside of the strip. The more of this clay we bank about the joint the more protection there is. When the above has been done, the object must be left in some warm place until the moisture from both the enamel and the clay is thoroughly evaporated. It is then ready for firing. If the blow-pipe or the Bunsen burner is used, take a tripod and place a piece of heavy iron netting over the top and place the object on top of the netting. The flame should always be applied to the under side. Watch the enamel as the firing goes on and when it settles and glazes the heat should be withdrawn. The object should be allowed to cool very slowly.

Hurrying at this point only increases chances for accidents. If, when cool, it is found that the channels in places are not full of enamel, the object is again cleaned in the nitric acid, more enamel applied, and fired as at first. The cover is now ready to finish. The enamel may be stoned down level with the top with an emery stone, or it may be left just as it comes from the fire in the first place. If stoned down, it is necessary to fire it again just enough to give it a glazed surface.

The directions as given apply to either transparent or opaque enamel; but, in addition to the above, when transparent enamel is used, the surface to be enameled must first receive a coating of flux to retain the transparency. The flux is treated and applied just the same as the enamel already described.

The upper half of Plate 26 shows boxes treated with enamel.