Etching has many uses in jewelry making, and it is a quick and relatively easy process. The aim is to use an acid solution, known as a mordant, to eat or dissolve away exposed sections of metal. You can obtain different depths, depending on how long the metal stays in the mordant. If a decorative surface is required, the depth of etch need not be very great. If, however, the depression is to be used for enameling or for laying in resins, the etch will need to be deeper between 1/100 and 1/50 inch deep.
Always remember that the acids used in etching can be dangerous. Always handle them carefully and sensibly. Keep them in clearly labeled containers and store them under lock and key.
Types of resist
A resist is a substance that protects the surface of the metal against the active properties in the mordant. 'File most common resist is called "stop-out" varnish, which is thickish bitumen based liquid painted directly onto all areas on the metal that need to be protected. Support the work on a little stand so that you can apply the varnish without having to touch the metal, and when the front is dry, turn it over and paint the other side. Remember to paint all edges with the varnish. Any cleaning up, such as straightening wobbly lines, can be done when the varnish is dry by drawing the edge of a sharp blade down the line and gently lifting or scraping away excess varnish.
Make sure that the varnish is completely dry before placing the piece in the etching fluid.
An alternative resist to varnish is beeswax. Melt the wax into a small tin, warm the metal, and dip it in the wax, which will coat the metal in a thin, even layer. When the wax is cool, cut or draw the pattern through it.
If you want a decorative or pictorial effect on metal, you can use a hard or a soft ground "stop out." This is a mixture of beeswax, bitumen, and rosin, and it is applied to the warmed metal with either a leather dabber or a fine cloth bag containing the ground. The ground is spread evenly over the metal with a small roller. Lard ground is then treated in the smoky end of a candle flame, which is played over the "stop-out" until it darkens. When the ground is cool, the picture or pattern can be drawn through it with the tip of a tapestry needle or a special etching needle. A coat of ordinary "stop-out" is then painted over the sides and underside of the metal.
Preparing the metal
Before you apply the resist, the metal must be cleaned thoroughly with pumice powder paste or by rubbing with wet and dry papers under running water. If the metal is not completely clean, the varnish will lift when it is left in the mordant, exposing the metal that you wanted to protect.
Depending on the intricacy of the design, the pattern is transferred to the metal either before or after it is cleaned. If the design is complex, rub the surface of the metal with putty or clay and trace the design onto it. Remove the tracing paper and scribe through the lines with a sharp metal point. Then clean the metal thoroughly. For a free-form design, clean the metal first, then draw on the design with a sharp lead pencil, but take care not to touch the metal with your fingers.
Preparing the etching fluid
You will need to make up solutions of different strengths according to the metal you are going to etch.
1 part nitric acid, 1 part water, or 2 parts potassium chloride, 10 parts hydrochloric acid, 90 parts water.
3 parts water, 1 part nitric acid, or, for a longer, slower etch 5 or 6 parts water, 1 part nitric acid.
Gold 18, 14, and 9 carat
8 parts hydrochloric acid, 4 parts nitric acid, 1 part iron perchloride, 40 or 50 parts water (aqua regia) or 2 parts nitric acid, 2 parts sulfuric (or hydrochloric) acid, 4 parts water. Gold will not dissolve in the etching fluid for silver or copper.
Using the etching fluid
Mix up the mordant or buy it ready-mixed. When you are working with etching fluid, always wear, in addition to protective gloves, safety glasses and an apron. Work in a well-ventilated area because the acids will give off strong fumes. Mix enough mordant to cover the piece, but do not mix more than you need. An ovenproof glass bowl is suitable for all these mordents. Use stainless steel or plastic tweezers to place the piece of metal in the mordant, and then watch the reaction of the fluid on the exposed metal. If it is too violent that is, if a lot of bubbles rise quickly to the surface the mordant may be too strong. Dilute it by putting 1 or 2 parts of water in another dish and carefully transferring the mordant to the new bowl. Generally, the etch will take between 15 and 30 minutes, depending on the strength of the mordant and the depth required. If you are doing a very long, gentle etch, the metal may need to be in the mordant for 3 hours.
In addition to etching downward, the mordant bites sideways into the metal, once it has penetrated beneath the "stop-out." A slow etch helps to overcome this problem to some extent, but you should take this "undercutting" into account when you prepare the design, because it can result in some fine lines becoming rather ragged.
To test the depth of the etch, remove the metal from the mordant, then rinse and dry. Run the fine point of a steel scriber over the surface and into the etched areas to get a feel for the depth achieved thus far. If the piece needs further etching, check to see if the "stop-out" needs retouching. If it does, remove any flakes of varnish, dry thoroughly and lift any raised areas with the blade of a craft knife. Repaint the area or areas with varnish and make sure it is completely dry before returning it to the mordant.
Cleaning and finishing
When you are satisfied with the depth of the etch, remove the piece from the mordant and rinse it thoroughly under running water. Store the etching fluid in a clearly labeled glass jar or put a lid on the bowl. Although mordant can be re-used, it will turn a clear deep blue-green when spent. When this happens, dilute it with as much water as possible and dispose of it, again in running water. Dry the washed metal with paper towels before either wiping it with mineral spirits or turpentine or leaving it in a shallow bath of turpentine. Remove a beeswax "stop-out" by holding the piece over the tin of wax and heating it with a gentle flame so that the wax drips back into the tin.
When all traces of "stop-out" have been removed, clean the piece with pumice powder paste, which can be applied with a toothbrush. Clean up any ragged lines with a "Spitstick" engraving tool. If the piece is to be enameled, rub all over the etched area with a glass-fiber brush and then use a polished burnisher to brighten the area.
This process, which is generally carried out by commercial firms, is particularly suitable for work that is to be enameled or that involves a lot of intricate piercing of several pieces. Photoetching involves photosensitizing metals to produce a "resist" and to printing an image that can then be attacked by a suitable etching fluid. When it is used to make jewelry, photoetching is an extremely accurate process, as long as a number of guidelines are observed.
Most photoetching firms prefer to work on a sheet of metal that is not smaller than about 12 x 18 inches, so the design needs to be carefully considered and the number of items required needs planning to fit into the area. The etch can then be taken to an accurate depth, and if the sheet is no thicker than 1/22 inch, the etch can pierce through the metal for either decorative purposes or to save piercing out the item later.
When you are designing for photoetching, the image should be drawn and painted to about twice the size of the finished piece. The final artwork can be reduced to half size, either by photocopying or by the grid method. The solid, colored area represents the metal that is going to be etched away.
When you present the finished design to the photoetching firm, remember that:
• The design should fit on a sheet about 12 x 16 inches, with a margin of about I inch all around.
• The areas to be etched should be shown in solid red, and the depth of the etch required noted in writing.
• Areas to be pierced through should be shown as solid black lines.
• If you are using black lines for areas to be pierced, make sure that the metal is no more than V32 inch thick.
• If you are assembling a design from several sections, make sure that you white out all the edges, so that they do not photograph as black lines.
• Use the sheet of metal as economically as you can. It is rather wasteful if you get only two or three pieces from one sheet.
Writer- JINKS McGRATH