Chapter XIX: Enamelling

Enamel is a glass fused to the surface of metals, for decorative purposes. It is bought in flat discs about 1/4 in. thick and weighing from 5 to 6 ounces. These discs are broken up so that one is able to buy enamel in small quantities. It comes in any colour and when put upon the surface correctly the colour does not change and it is not affected afterward by atmospheric influences.

_Tools:_ One needs few tools for this work. A wooden mallet, a mortar and pestle, and a small spoon used to put the enamel on the metal when filling the design will be found sufficient. The spoon may be made by taking a 1/8-in. piece of silver or copper wire with about 1/2 in. of the end flattened down spoon shaped. File this end round and smooth so there will be no ragged edges.

_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.

IMITATION PATINA (GREEN TINT ON COPPER)

The best method of obtaining a coating resembling patina is to immerse the article in a solution of nitrate of copper, and then to place it while still wet in a chamber containing an abundance of carbolic acid. In this case the development of the green incrustation may be observed from day to day. If after a week the object has not yet obtained the proper colour, it must be again dipped in the above solution, and this operation is repeated till the desired shade has been acquired. As the formation of this green colour proceeds in the same way as in the open air, but more rapidly, a handsome and permanent coating of green can be produced by this means.

CHEMICAL METAL COLOURING

_How to put a thin coating of colouring on the surface of metals by chemicals:_ A great variety of shades may be obtained simply through heat. The colours ordinarily produced on copper articles by means of heat come through the polishing. Any metal whose surface is highly polished will take on a number of different colours, beginning at a straw colour and changing to a dark straw, purple, dark blue, light blue, and steel or gray, by heating the piece to be coloured to a temperature of 630° F.

_Barium sulphide and water (a very good composition for colouring metal):_ Immerse object until it assumes desired tint from light brown to violet to black. Heat gently over bunsen flame until a rich deep violet appears. After it is cool rub with soft cloth.

_Patina imitation (a very good composition for the greening of copper):_

1 part sal. ammoniac,
3 parts cream tartar,
6 parts salt,
12 parts hot water,
2 parts nitrate of copper.

Saturate soft cloth and rub or sprinkle the solution on the copper. Let stand in the open air ten or twelve hours. Wash the colour off with clear cold water. Tone down to suit.

Another way of colouring metal.

Silver.

_To oxidize silver:_ The following is a solution commonly used for oxidizing silver:

Potassium sulphide, 5 grains,
Water, 10 fluid ounces.

The variety known as liver or sulphur is generally used, and imparts a reddish brown colour to the silver, the colour being darker the darker the solution. It should be worked at 60 or 70 per cent. The stronger the solution the blacker the colour. If ammonium carbonate (20 grains) is added to the above formula and is worked hot, a black colour appears upon rubbing with a very fine wire brush. It takes on the colour of black lead.

_Colouring of brass:_

Copper sulphate, 2 ounces;
Water, just sufficient to dissolve the copper sulphate;
Ammonia, to neutralize and make slightly alkaline.

This will turn brass a very beautiful blue-black colour. Copper assumes a very beautiful tint from this solution.

_Cement for engravers:_ Melt best pitch in an iron pot and when completely liquid stir in a mixture composed of two thirds of raw pitch and one third plaster of paris. Make a lot of ten pounds. Add one half pound mutton tallow, boil and mix thoroughly. Should this be too soft, add plaster of paris until you get the desired hardness:

5 lbs. black raw pitch,
5 lbs. plaster of paris,
1-1/2 lbs. mutton tallow.

_To polish enamel:_ After rubbing it down with the corundum file, take a small rod of tin or pewter and after anointing it with fine Tripoli or rotten-stone, grind the surface of the enamel evenly with the tin or pewter rod. Next take a stick of lime wood and use that with the rotten-stone in the same way and finish with putty powder and stick covered with chamois skin.

_To unsolder a piece of work:_ Paint those joints which are not to be unsoldered with a mixture of clay water, to which add a little common salt. When dry, scrape the part to be unsoldered and paint it with borax. Now heat till solder melts, pick off with pliers or knock it off with a gentle tap. The borax adds flux, thus helping the solder to run at a melting temperature.

MACHINERY IN METAL WORK: DIE MAKING

Most of the jewellery that we see nowadays and also much of the metal work is made under presses or drop hammers. As was shown in the making of the mould for the round copper tray, the skill lies in the making of the design and the making of a mould to fit the design.

The description of the making of a match safe by means of die sinking will explain how all die work is done: The design for the match safe is made by the artist, who turns it over to the die sinker. He, in turn, chisels out of a steel block, about 7 ins. square, a depression in which the design fits. If the match safe has an embossed design, this is all chiselled out carefully with small chisels and filed up smoothly so that when a piece of soft lead is driven into the depression it will take the shape of the match safe as designed by the artist. The lead is so soft that it takes the print readily. This lead reproduction shows to the die sinker any imperfection in the die. The imperfections, if there are any, are smoothed down. The driving in of the lead into the depression is repeated from time to time, until the mould is the exact reproduction of the artist's design.

The die is now hardened by heating it red hot and cooling in water. When taken out of the water it is placed in the hammer or press. On the ram of the hammer is keyed, directly above this die, a square block of lead. When the hammer falls, the impact of the lead upon the impression produces a reproduction of the impression. This lead piece makes the top die. A piece of thin silver is placed in the steel die over the impression. If the ram is now dropped upon the silver plate it will force the plate into the impression and will stamp the design on the silver. One half of the match box is made in this way. When two of these are made, put together, and soldered, they make a whole match box. Thousands of match boxes would be made from this one die. That is the reason why this class of work can be sold so cheaply.

The principle explained here is used for the making of tea sets, dinner sets, etc. The same thing is true of the round wood mould you made to make the copper tray in. It can be used to make dozens of trays, all the same size and shape.

GLOSSARY

_Alloy:_ Base metal added to silver or gold for hardness or colour. Also any combination of different metals by fusion.

_Annealing:_ Softening metal by making it red-hot and cooling slowly; for steel, brass, copper, silver, cooling quickly in water.

_Backing:_ The coating of enamel on the back surface of box lids, to neutralize expanse and contraction, thus preventing top enamel from cracking.

_Basse-taille:_ Low cutting of metal beneath the line of the surface, used in enamelling. The drawing or modelling of the subject is given by the different depths of cutting.

_Beck iron:_ T-shaped anvil or stake used in hammer work. The arms of the T are long; one is round and slender, and tapering; the other has a flat upper surface.

_Bossing up:_ Beating out sheet metal in the back into rough forms required.

_Champlevé:_ A process of enamelling on metal in which the ground of the pattern is cut away with a chisel into a series of shallow troughs into which the enamel is melted, the surface being afterward ground smooth and polished.

_Chasing:_ Surface modelling of metal with hammer and punch or chasing tools.

_Cloisonné:_ An enclosing ribbon wire, which being soldered edgewise on a metal ground makes a trough into which enamel is melted, the ribbon making the division. Thus the design is separated.

_Collar:_ A ring made of stout leather filled with sand or some other soft material used to support the pitch block.

_Draw Plate:_ A flat plate of steel or iron with rows of graduated holes, used for drawing or reducing wire.

_Face Plate:_ A square thick iron plate with the surface perfectly smooth and level to test work on.

_Flux:_ Any material used to protect the surface of metal from oxidation when exposed to heat. Borax and water mixed, etc.

_Graver:_ A kind of small chisel used for cutting metal, or lines on surfaces.

_Mandrel:_ A rod of wood or iron of any section used either for coiling wire for chains or the making of rings. _Matt tool:_ A punch, flat and graduated on one end, used for making groined surfaces on metal.

_Pickle:_ Solutions of various acids in water used for removing the film of oxide and sulphide surface of metal. The acids used are nitric acid, hydrochloric acid, and sulphuric acid, about 8 to 1. This is strong enough for ordinary work.

_Pin:_ The hard wood peg fixed in the bench to hold work against to file and fit.

_Pitch block:_ Some iron blocks and wood blocks covered with pitch used as a support for metal in repoussé work or chasing.

_Planishing:_ Beating a plane or level surface to a sheet of metal by the use of a broad smooth-faced hammer on a stake or anvil. Also used to give smoothed face to a bowl or cup or other object in sheet metal.

_Repoussé:_ The method of beating out sheet metal from the back with hammer and punches.

_Sand bag:_ A flat circular or square bag of leather filled with sand used for bossing up metal upon.

_Scraper:_ A tool made from an old file by sharpening the point on a stone to a three-sided pyramid; used for scraping clear edges and surfaces to be soldered and for cleaning up work generally.

_Snarling iron:_ Long Z-shaped bar of iron fixed in a vise and used for bossing out the surface of vessels from the inside. They act by rebounding from the blow of the hammer near the end fixed in the vise.

_Tracer:_ A chisel-shaped punch used for cutting for any design or work that requires deep lines.

THE BLACKSMITH'S SHOP