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Electroetch Articles |
| PRINTMAKING TODAY LEONARDO 25 |
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Electroetch Articles |
| PRINTMAKING TODAY LEONARDO 25 |
| CHEMTECH April 1991 pp. 210-214 Come up and see my (ecologically safe) etchings! (Posted with permission from CHEMTECH, April 1991, 21(4), 210-215 Copyright 1991 American Chemical Society) Omri M. Behr and Marion R. Behr Right-brained people intuit and left-brained people deduce by logic. So when an artist and a scientist marry they usually continue to do their own work in their own ways. In a long marriage, one realizes that it's easy enough to agree on goals and not worry too much about reasons. Sometimes an important idea pops up on which both have to focus their particular skill and thought patterns at the same time. This, apart from our children, has happened to us twice. About 10 years ago we bought an old farm in the Catskills. The property was so rundown and waterlogged that we were sure we saw mosquitoes in mid-February. Restoring it became a labor of love, We laid out and cut new stream paths, built a pond, planted 10,000 spruce trees and the kids even pulled up the pine floorboards from the old house for the new one. We merged basic engineering principles and artistic vision to enhance the beauty of the place while maintaining its ecological integrity. Last year we decided we wanted to build a complete print studio in our barn. It was to include a press as well as all the facilities needed to etch copper and zinc plates. The press had to go in the concrete-floored basement and not in the hayloft, which had the prettier view. However, what about the chemical end of the operation? When we talked about this with some of our friends, we realized that because the land is in the New York City watershed, we would have to find a way of getting rid of the acids and heavy-metal solutions that are used and produced in metal etching. Could we find a way to etch that was kind to the environment and ourselves? There has been no major change in the process since the introduction of Dutch Mordant in the nineteenth century. Rembrandt would still recognize the way etching plates are made today, because the basic process is about 400 years old. Metal printing plates, called intaglio plates, are made in two basic ways, using either engraving tools or acids. The acid method is commonly known as etching (1), an artistic catch-all that really includes three related ways of treating a metal surface so that it holds just enough ink to transfer an image from the plate to paper. These methods are bard- ground etching, soft-ground etching, and aquatinting. The first includes the creation in the metal of lines and lowered surfaces called embossments. The second provides a way of texturing the surface and the last, aquatinting, involves treating selected areas so that they will print as different shades of gray. Traditional methods of etching can harm both the artist and the environment. Acid fumes can irritate the lungs and make contact lenses stick to the eyes. The rosin dust used in aquatinting forms a permanent layer in the lungs and can eventually cause incurable breathing problems. Heavy- metal solutions are harmful to municipal or septic tank sewage systems. Many artists do not realize these dangers and most studios probably do not meet the safety standards of modern laboratories. Acid baths, which may have open surface areas of 6 square feet or more, are not always covered by fume hoods. Nitric, hydrochloric and perchloric acids, used for etching copper or zinc, are dangerous, not only because of evaporation, aerosol formation and spillage but also because the metal-acid reaction can form nitrogen dioxide and chlorine. Often, an artist lives in his or her studio, so that everyone in the household is at risk, including small children. Pregnant women have stopped their etching work for fear of harming their unborn babies. One key to the solution seemed to be to take acids out of the process. With this hazard out of the way, artists would he able to etch in many places where it is not now safe to do so. Indeed, etching might even be introduced in high school art classes. Looking sideways. In all etching processes, acid removes metal from a plate because the electrochemica] balance favors the ionic rather than metallic form of the metal, Etching, which actually means "to eat," (2) has always been regarded as a chemical process. However, understanding the interaction of acids and metals calls for knowledge of the electrochemical nature of the reaction. What would happen, we thought, if we looked at the electro, rather than the chemical, picture? This sideways thinking opened the door to the answer, confirming our view that successful invention requires both a sense of the path to be taken and a basic grasp of the general subject matter. The following equations show the chemical steps that occur in acid etching of metal: Zn + 2HNO3 à Zn(NO)3 + H2 or Zn + 4HNO3 à Zn(NO)3 + 2NO2 + 2H2O or 5Cu + 2KClO3+ 12HCI à 5CuCI2 + 6H2 + Cl2 + 2KCI All of these steps leave unused acid and metal ions in the bath. Each of these reactions forms a dangerous or harmful gas: hydrogen, nitrogen dioxide, and chlorine, respectively. These gases can also evaporate the acid or form an aerosol containing it. A well-known and very different way of dissolving metal takes place in electroplating. When metal dissolves at the anode of an electric cell it becomes a positively charged ion. The ions reconvert into metal at the cathode when they give up their charge. We can write the electrochemical equation for zinc and copper as follows: Zn - 2g- à Zn2+ (anode) Zn2+ + 2g- à Zn (cathode) and, similarly Cu - 2g- à Cu2+ (anode) Cu2+ + 2g- à Cu (cathode) The amount of metal dissolved in the solution does not change, so it is reusable. There is no acid and, if properly handled, the process forms no gases. Could we use this knowledge to find a way to etch our metal plates? Our first experiments were run at the farm. The car battery was the power source, the metal plates were flattened "D" battery cells and the electrolyte was a filtered solution of the zinc chloride gel scraped from the inside of those cells. The cathode was the carbon rod from the cell. We got some nice etching. but two hours later, after the electrolyte in the coffee-cup bath had boiled and the car wouldn't start, we decided that slightly more sophisticated power sources and controls would he in order. Because the idea worked, we did a prior-art search to see what was already known. We found that the principle behind these electrochemical steps is not new. In 1912, Schwuchow and Johnston (3) obtained a U. S. patent for a process of making halftone zinc plates by using plates carrying photoresist layers as anodes in an electrolytic cell. Anodic etching has been used for many different applications since then (4-8). Interestingly, we found that no one had used these approaches to get the fine control of line depth and width required and given by the conventional acid etching processes. Also, no one seems to have considered whether the aquatint effect could be achieved without using rosin or a similar intermittent resist surface. The most recent books on printmaking (9, 10) deal at length with the intaglio processes. Because neither of them mentions electrochemical etching, clearly this approach is novel. Our work, done at home without the aid of modern laboratory facilities, resulted in an ecologically safe, acid- free etching process and an apparatus for carrying it out (11). One hazard should not be swapped for another. The known anodic etching applications use low voltages, in the neighborhood of 10 volts, so the electric power level itself is no problem. The chemistry in an electrolytic cell can become quite complex because the various ions compete with each other at the electrodes. At the 10-volt level, the most common of the "successful" ions in a water-based solution form hydrogen at the cathode and oxygen at the anode. H2O à H+ + OH- 4H+ + 4g- à 2H2 (cathode) 4OH- - 4g- à 2H2O + O2 (anode) and 2H2 + O2 à 2H2O The hydrogen and oxygen of the last equation are an obviously explosive combination, but we avoid their formation by keeping the voltage low enough so that the competitive electrochemical balance prevents their generation. The amount of current that flows depends on the voltage as well as on the concentration of the metal ions in the solution. High voltages together with high ion concentration (say above 1 M) lead to the formation of oxygen at the anode, which is not given off as gas, but reacts with the metal. 2Cu - 4g- + 4OH- à 2H2O + 2CuO (anode) This reaction would stop further etching from taking place because copper oxide does not conduct electricity. Electroplaters therefore keep down the voltages to permit plating to continue smoothly at the cathode. We do the same with our voltages. We found that even very low voltages etch a printable line into a drawn-into hard-ground covered copper plate in 5 minutes. It is better, though, to etch for a bit longer, say from about 1~60 minutes (Figure 1) (12). The etch lines we obtain electrolytically appear bright compared with the dull acid-etch lines and hold the ink more efficiently. When we look at our etch lines with a magnifying glass (about 8x), we see what seems to be a crystalline surface structure. We do not see this at higher voltages, such as 10 volts. This explains the more efficient retention of the ink. Because crystal masses react more quickly at fault lines, edges and where surfaces join, the metal should dissolve faster at the fault lines than at the surfaces of the crystals themselves. We thought that the gentle nature of very low voltage etching might encourage this difference. Scanning electron micrographs (13) showed that our ideas were right. There is a surprising difference between the surfaces of metal etched in the traditional acid bath and by this process. Figures 2 and 3 are 500x magnifications of acid and low-voltage etches of a portion of a single etched line. The acid-etch surface has a far more regular appearance than the electrolytic etch. Figure 3 clearly shows the different levels of erosion of the crystalline substructure of the metal. Creating different effects All the traditional ways of etching require the complete or partial covering of the metal plate with a resist, after which exposed metal is eaten away by acid. In hard- ground etching, the resist is firm and waxy. The lines, independent, connected, or cross-hatched, are lightly drawn into the ground. The plate is then placed in an acid bath, usually for ~0-60 minutes, depending on the strength of acid and the depth of etch desired. To produce embossments, larger areas are left uncovered and the etching continued for several hours. Surface texturing uses a slightly different formulation of the wax, known as soft ground. Texturing is achieved by placing a material, which can be a piece of cloth, a flower stalk or a petal, on the ground and then running the combination through a press, which exposes some of the metal. A different type of texture effect occurs after drawing on a sheet of grease-resistant paper, previously placed on the soft ground, so that the drawn design is impressed through the ground. The plate is then, as before, placed in the acid bath, but usually for rather short periods, say 10-20 minutes. Aquatinting is the most common way of preparing a surface to print shades of gray. This process calls for coating a finely separated resist on the plate, which can be done with a fine aerosol spray of enamel paint. More usual, however, is the use of a rosin or asphaltum dust deposit, either by putting the rosin in a fabric mesh dust bag shaken over the plate or by using a rosin box to deposit the particles on the plate. Careful heating of the etching plate on a hot plate (below 250 0F for rosin and below 500 0F for asphaltum) just melts the particles, but not enough to form a film. Acid treatment of the plate then etches out the uncoated metal. To create a design of different shades of gray, selected areas are successively "stopped out" with hard ground or stop-out varnish and the plate reimmersed in the acid at each stage. The most exposed areas will have a much coarser grain than the least exposed ones. Thus they will hold more ink and print darker. The rosin/asphaltum process requires considerable experience to coat the plate with just the right quantity of particles of the right size and to heat them properly. if the plate is in the acid too long, the plate will "white out, which means that the acid will cut under the rosin, leaving fewer retention areas for the ink. The process is also unhealthy. The dust bag simply releases the rosin into the air and in the box method, the box must he opened twice. Workers who use rosin ought to wear masks, but many just don't bother. An interesting way of making etched plates that have a painted appearance, as opposed to those that look drawn, uses both aquatint and a sugar lift coating. The sugar lift mixture (commonly one part of gum arabic, two parts colored tempera paint powder, 40 parts corn syrup, and three parts liquid detergent) is painted onto the plate either before or after rosin treatment when the mixture is dry, and a hard-ground coating is placed over the entire plate. The plate is then soaked in water until the sugar layer is washed out. The exposed metal is then aquatinted. The basic principle of aquatinting calls for the creation of tiny pits between the rosin or asphaltum particles to hold the ink. Because the Electroetch process created a crystalline surface in the etched lines, the same effect should occur on the surface of a plate, if it were treated in the same way. We were delighted to find that we had guessed right and were rewarded with a rosin-free aquatint-like effect that we call Microtinting. By applying the low voltage to an open, clean metal surface we obtain, predictably and reproducibly, beautiful arid substantially uniform grained surfaces. When printed, the shades ranged from the palest gray to a deep black. Figures 4 and 5 illustrate some possible variations (12). Unlike aquatinting, Microtinting does not carry the potential danger of whiting out. The longer the current passes, the progressively darker the shades of the print become, even though after about three hours there is usually no further noticeable change. Microtint can also be used with soft ground and sugar lift. One can also draw the resist onto the plate using, say, a lithograph pencil. The imperfections of these pencils lead to attractive effects. However, such resist layers do not have the strength of hard ground or stop-out varnish and, after a time, will allow the current to pass. Where the metal is not resist-coated, simple or complex designs can be cut into or straight through the plate in about 25-30 hours (Figure 6) (12). The sides of these cuts are usually perpendicular to the face of the plate with no 'breakthrough contamination of the front face. Depending on the resist chosen, the cut edges are rough or smooth. The key to success in Microtinting lies in the strict but simple control of a number of factors. All the old ways of plate surface preparation for acid treatment, such as cleaning, polishing and avoidance of grease or even finger marks still apply. Because the new process is a gentle one, a misplaced thumbprint becomes very visible on a surface treated to print as a pale gray. Controls of voltage, current density and bath temperature are all important. During the etching of small areas, the heat released by the flow of current in the bath does not matter too much, but it is a factor when cutting or embossing large plates, particularly when the studio's ambient temperature is high. As In conventional etching, a good seal must exist 'between the resist layer and the plate. A rise in bath temperature to more than about 90 oF may permit electrolyte leak between the metal and the resist layer, which may make the difference between a clean and a dirty plate. A resist coating still needs to be carried on all parts of the plate, including the rear surface, that are not to be etched. The pH needs to be controlled as well. Making the print After the plates have been etched, they are then inked. An ink paste is rubbed into the surface of the plate with the edge of a piece of card and then much of it is scraped off with a similar clean card. Most of the rest of the ink is then removed with a softened piece of tarlatan. Some able printers then wipe off the remaining excess with the edge of the hand or the palm below the thumb. One must leave just the right amount of ink in the etched lines and textured surfaces, while leaving virtually none on the untreated parts of the plate. Plate wiping is, and probably always will be, a work of great skill, The specially absorbent paper is prepared by soaking it in water and drying it to slight dampness. The plate is then placed face up on the bed of the press, the paper (watermark side down) is laid over it and covered with felt blankets and the combination passed between the rollers of the press. The paper is then removed from the plate and dried under a flattening force between sheets of absorbent paper. We believe that our new process will make life safer and healthier for the artist and the environment. It will also open up a beautiful art form to many who could not enjoy it until now.
Marion B. Behr is an internationally recognized graphic artist who has worked from home for many years. She is an advocate for and authority on home-based business and is the co-author of "Women Working Home," She received her MFA (Painting) from Syracuse University. Omri M. Behr is a partner in the patent law firm of Behr and Adams (325 Pierson Avenue, Edison, NJ 08837-3128; 732-494- 5240). He holds a BSc. and M.A. from Christ Church, Oxford University, a Ph. D. in Organic Chemlstry from Glasgow University, and a J.D. from Seton Hall University. He is a Fellow of the Royal Society of Chemistry (London). References
Figures 1,2,5, and 6 are Copyright Marion R. Behr 1990. Figures 2 and 3 are Copyright Omri M. Behr 1990. Reproduction rights are limited to copying as part of this article, |
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