Photo etching

Introduction to photo-etching

Gertrude Käsebier, Serbonne, photogravure, 1903

Photography has always been linked to printmaking and, to tell the truth, its advents has affected all the art media, offering the unexpected chance to reproduce reality as it is. All of a sudden, art was no longer a matter of mimesis and the querelle about realism and truth in art became meaningless. As any new discovery, photography seemed incredibly appealing and traditional fine arts sought a confrontation. In particular, printmakers wanted to apply the principles of photography to the graphic media (intaglio, lithography and soon after to screen-printing) because they knew that, if they succeeded, not only artists could make innovative prints but above all the entire production of commercial prints (newspapers, posters, books et cetera) could increase and become easier and faster. Photographic engraving, heliogravure, halftone screen engraving were only a few of several ingenious late XIX Century etching techniques related to photographic procedures. During the last twenty years of the Nineteenth Century, printmakers were constantly conducting experiments to create photosensitive gelatins to put onto the plates and work exactly as in photography. Their efforts were fruitful and, with time, a wide range of photomechanical techniques was brought to perfection. Sadly, in the years after the Second World War and especially in the Sixties and Seventies, photomechanical etching media fed the market of fake artworks or were used to swindle collectors and sell photo-etchings as pure etchings with a sensible difference in price. Some artists and some printers were equally willing to turn a blind eye. Thus, photo-etching was shunned for a long period and an international debate regarding the definition of what is to be considered original has dominated the critical discussion since then.

Photo-etching today

Anna G. Torfadóttir, Fjaðurmagnaður, pianoincisione - collografia - linocut, 2007

At the present time, it is important to again reinforce that etching (as well as printmaking in general) is an original art form far from processes such as gicleé (inkjet printing), which merely copy or reproduce at a push of a bottom an already existing piece of art. Can photomechanical processes find a stimulating application within the frame of originality? It definitely seems so and photo-etching is facing a positive season.

Photo-etching adopts photography to get an image onto the plate before etching, using a film positive and exposing a photosensitive matrix to UV light. The film positive, placed in direct contact with the matrix, lets the light through the clear areas (where the gelatin hardens and becomes acid-resistant, protecting the metal from the bite) while not through the black areas (where it remains soft and will be washed away by the developer, exposing the metal to an aquatint and to the bite). The main point is to not conceive the film in an ordinary way. It can be photographic (in this case it is called a lith-film) or autographic (and therefore it can be drawn, painted, assembled like a collage) or a mixture of both. Working on a film itself does not frustrate originality nor creativity, as well as a photomechanical process does not necessarily coincide with reproduction.

A further useful consideration is that photo-etching has radically changed in the past ten or fifteen years. Most of the toxic methods used earlier (that demanded the use of caustic soda or neg jet as developers) have been banned or discarded, in favour of safer practices. Photo-etching counts today several media, some of which are based on the ultimate innovation based on photosensitive polymer plates that are water-washable and require a mild solution of water and washing soda as developer. This is the most environment-friendly and health-safe process that printmaking has ever adopted.

Continuous-tone and half-tone

Kristín Pálmadottir, The Power of Nature, photosensible polymer etch, 2007

The difference between continuous-tone and half-tone images is essential in terms of artistic style and image constructions, determining unique and unmistakable results. Photography is a process that obtains continuous-tone as well as photogravure, the earliest photo-etching technique discovered and the only type of photo-printmaking that uses a continuous-tone positive film. On the other hand, photo-etching, photolithography and photo-screen-printing all use a half tone positive film, which means that they only recognize black and white. Greys are obtained by using a series of dots, often computer-generated. Half-tone screens are usually very mechanical and are made up by lines or nets of dots; an exception to this is the stochastic random dot screen (also known as mezzotint half-tone) that is used with some photo-polymers to create a virtual aquatint (see below). Half-tone screens have two units of measure: lpi (how many lines of dots) and dpi (the definition of the computer generated screen). If a computer is being used to create the film positive, it is possible to create the image with a half-tone texture, to print it on acetate and use this as film positive. If the image is being transferred on a photocopy, it is possible to add the half-tone texture by selecting this option on the photocopier and photocopy the image onto acetate or even tracing paper. With common photocopies or computer prints it is likely that the light will also partly pass through the black areas, this is why in such case it is preferable to do a small test plate to determine the exact exposure. With a lith-film positive, the process is more accurate.

Photo-etching is easier that it may seem at a first glance. It is advisable to try out rudimentary techniques to have a go and then, if interested, to set up a good and safe studio to work with the most advanced techniques.

Basic transfer and photo-etching methods
(not requiring specialist equipment)

Lazertran
It is possible to do a transfer or a simple photo-etching by photocopying the image onto the shiny side of lazertran, a rather inexpensive transfer paper sold in fine art stores in A4 or A3 size. It goes through all the photocopiers, but it performs best if printed black and white with a colour photocopier. The toner works as an acid resist. All it requires is water, turpentine and soap. This is the improved procedure based on the transfer of photocopies.

Transfer of photocopies
If lazertran is not available, another option is to work with common photocopies, although old photocopiers used a thick and greasy toner which was perfect as an acid resist but the last generation machines have water-based toners and they do not always work. Working with photocopies is very hit or miss and the quality of the result varies tremendously, according to a number of factors. It must be remembered that when you work with transfer, the initial image is the negative of what you will get in the final print. A banal but clear example is the transfer of a text: if your photocopy is a black text on white background, the final print will be the exact opposite: white text on black ground because the toner stops the areas of the black fonts, while everything else is aquatinted.

Neg jet
Neg jet is an engraving quality zinc, much finer that roofing zinc, which is pre-coated with a light sensitive emulsion. The coating is even and consistent. Exposing neg jet plates is reliable after an initial test plate has been done. The downside is it is very expensive and the developer is quite toxic.

Aqua blue

Geoff Johnson, Winterlight & Wintertrees, solarplate, 2007

Produced by the same company that produces neg jet, aqua blue is a safer alternative that does not require a ventilation unit for its developer. The product is just as expensive but the roll-on blue etch is safer and equally reliable.

RS photo-resist spray
This product is made for the circuit boards industry. It is supplied in an aerosol can and is sprayed onto a degreased plate. The spray is positive working, so the plate has to be negative exposed.

I listed all these methods as basic, in the sense that they do not require necessarily the access to specialist equipment. For simple photo-etching, the film (positive if you use neg jet or aqua blue and negative if you use RS photo-resist spray) can be kept in direct contact with the plate with a clean piece of glass. The exposure light can be a normal ultraviolet lamp (like a sun lamp), suspended 60 centimeters above the glass, film and plate. Ultraviolet light is dangerous for the eyes as it can cause premature cataracts. So leave the room during the exposure. Another option is to use a mercury fumes lamp, but also in this case protects your eyes and leave the room. All these sorts of lamps have a timer, so they switch off automatically. It is even possible to use sunlight to expose your plate, especially in the summer time or in a sun kissed country as Italy, yet it is obvious that sunlight varies continuously. So if it can seem a cheap alternative at the beginning, it will likely bring frustration and expense for the amount of failed attempts.

Advanced photo-etching
(Requiring specialist equipment)

Flexograph plates
Flexograph plates have been used commercially for letterpress printing since the Sixties, they consist of a layer of light sensitive nylon resin emulsion, backed with a thin steel sheet. When these plates are wrapped around the automatic printing drums, they are capable of printing millions of copies without wearing. They are capable of reproducing the subtlest hand-drawn marks as well as photographic images. These plates are extremely user-friendly because no chemicals are involved in the development process and they can resist for short periods in daylight, so a darkroom is not necessary. Certainly this is the best choice for homework or for school activities.

Liquid-etch-resist
Liquid-etch-resist is the best option if you are biting with nitric acid or ferric chloride. This is a thin and gooey blue emulsion that has to be applied to a degreased plate with a soft rub roller. The positive side of this is that you can work on plates that have already been bitten.

Photopolymer films: riston, image-on, pure-etch, photec

Kristín Pálmadottir, Við hafið I, photo polymer etch, 2007

Riston, image-on, pure-etch, photec are all photosensitive plastic films that are put directly onto the surface of an etching plate. They look, feel and work in a very similar manner and they are all thick enough to hold the ink even if the metal has not been actually etched. For this reason, when talking about photopolymer films, two techniques must be mentioned: the photo-etch and the non-etch. In the first case, the polymer is used almost as a stencil through which the acid is allowed to bite the metal (it works as the ground resist). In the second case, no acid is involved and the ink is held only by the “virtual aquatint” on the surface of the film.

Photogravure
Photogravure needs a special mention because it is the only type of photo-printmaking that exploits and obtains continuous tones. The photosensitive gelatin is called “carbon tissue” and it is made light sensitive by a solution of water and any of the following: ammonium bichromate, ammonium dichromate, potassium bichromate or potassium dichromate. They are interchangeable and equally harmful for inhalation or skin contact. Gloves, googles, and dust-mask must be used. The solution requires a dark room with yellow or red safe light and only in a darkroom it will be possible to sensitize the carbon tissue. On the matrix the blacks and greys will be obtained with an aquatint bitten by four different acid baths with different concentrations. The gelatin will be dissolved in different tempos and the bite will have gradual depths.