One of the simplest and most interesting processes in sheet metalworking is that of etching. It requires very,simple equipment, and will show to the student the value of careful, painstaking work. Of the many articles that can be made by this process, the making of a watch-fob or bag-tag is chosen for the first description of tools and processes.
The materials and equipment needed are:
1 piece of soft copper or brass 18-gage (Brown-Sharpe gage) ; a piece 12" by 12" costs about 50 cents.
Black asphaltum varnish, 10 cents. If you cannot obtain the varnish, get a small can of Sapolin, commonly called stove-pipe enamel, 15 cents.
Turpentine to thin the varnish, or benzine to thin the Sapolin, 10 cents.
No. 2 water-color brush, 5 cents.
Nitric acid, 10 cents.
1 piece of carbon paper, 5 cents.
1 machinist's ball pein hammer, 3/4 lb., 60 cents.
Banana oil, 10 cents.
1 can of lye, 5 cents.
Potassium sulphide, 10 cents.
1 pair tinner's shears, 10" long, $1.00.
1 small chisel, 10 cents.
1 block of wood.
1 shallow dish, to hold acid solution, 10 cents.
Leather for the strap of the fob or tag when finished.
All the necessary tools are shown in Fig. 2, and would cost about $2.00.
Fig. 2. These tools are all that are necessary to make the work shown in the photographs.
Having all our tools and materials, the next thing needed is the design. For the bag-tag, the best design is a simple monogram, similar to those shown in Fig. 3, remembering always to have the initial of the surname the most prominent. For the watch-fob, we may use either the monogram or a conventional spot design similar to those in Figs. 4 and 5, remembering in all cases that in etching it is better when the design is the raised part and the background is eaten away by the acid, also that the edge of the article whatever it may be, should always be left the full thickness of the metal. See Fig. 3.
Next cut off a piece of metal a little larger than the design, and transfer the design to the metal by placing the shiny side of the carbon paper next to the metal and then placing the design over it and tracing the design carefully all over with a hard pencil; then remove the paper and the design will be seen on the metal. If the design does not show clear, as sometimes happens when the carbon paper is old, warm the carbon paper slightly before using. Now place in a small saucer or butter dish a very little of the sapolin or asphaltum varnish, thinning if necessary with the benzine, naptha, or turpentine, and with the No. 2 water-color brush carefully paint the design, as shown in Fig. 3. Be sure also to paint the back of the fob, remembering that wherever the metal is left bare it will be eaten away by the acid. Now lay aside to dry, which will take from fifteen minutes to two hours, according to the condition of the varnish. The drying of the varnish, however, may be hastened by laying the fob in a warm place.
Fig. 3. Designs for bag-tag.
We have now to prepare the acid solution for the real etching in a rather shallow stoneware or glass dish. Mix the solution of one-third nitric acid and two-thirds water, and when the varnish on the fob is dry, place it in the acid solution. If conditions are right, the acid after a few minutes will commence to etch or eat away the metal that has been left bare. This can be told by the very small bubbles rising from the bare metal. If after five minutes' immersion in the solution the bubbles do not rise, pour in a little more acid. Sometimes it happens that the acid is fresh and strong and will etch too fast. This can be told by the large bubbles rising very fast, giving the acid almost the appearance of boiling. It also throws off strong yellow fumes. When this occurs, weaken the acid by pouring in more water.
Fig. 4. Watch-fobs.
Fig. 5. Watch-fobs.
After it is etched deep enough, which will take anywhere from thirty minutes to three hours, according to the strength of the acid, take the fob out of the acid and remove the varnish by either scraping it off with a scrap of copper or soak for about half an hour in turpentine, gasoline, or a solution of lye, when it will readily wipe off, and cut off the surplus metal with tinner's shears.
The design now looks flat and uninteresting, so beat up the design from the back by placing the fob face downwards on a block of wood and striking it with the ball end of the hammer. When there is a decided center of interest in the design, as in Nos. 1, 2, 4, 5, 9, Figs. 4 and 5, beat that up higher, making it more prominent. If the hammered effect is desired, hammer the edges and the design with the ball end of the hammer on a ball-shaped piece of iron or on the ball end of another hammer. This also stiffens the metal and makes it hard to bend.
Now we have to deal with the problem of fastening the leather to the fob. There are two ways of doing this, as shown in Nos. 6 and 4, Fig. 4. No. 6 has a piece left on the fob and bent backwards into a hook, as shown in the drawing, then passed thru a small the small chisel on the block of wood and file smooth with the small slit in the leather and hammered flat. The second and best way is shown in No. 4. which is to cut out a small slit in the metal w ith flat file. An easier but much slower way to get the slit in is this: After the design is etched deep enough, remove from the acid and dry, then paint all over the metal, leaving bare the slit, place back in the acid and let it remain until the acid eats clear thru. There is another method - that of sawing out with a jeweler's saw - but on account of the cost of the tools and breakage of saws, we will not consider that method at the present time.