Living in Japan which is the locus of substantial earthquake activity reminds me that health and safety precautions can never be absolute. Personally I accept earthquake risks and enjoy hot springs which come from the same source of geothermal activity. There is always an element of personal preference in the risks we choose to accept, and those we try to control. The following recommendations are based on the idea of minimizing the risks of various hazardous materials in the printmaking workshop.
The main hazards in photogravure etching and related techniques are strong acids and alkalis, organic solvents, dusts and powders, dichromates, and ultraviolet light. Widespread use of the term 'non-toxic' is misleading in that toxicity depends primarily on how a substance is used, the degree of exposure, and dosage. Even the most harmless substances can be dangerous, as with water and drowning. In the etching workshop, rubber gloves, lab aprons, and ventilation and/or inhalation masks are recommended for ALL chemicals, whether toxic or non-toxic. In photogravure etching, we use ferric chloride as the etchant. Chemically, this is actually a salt, not an acid. Ferric chloride is relatively harmless, but since it leaves stains, it is best to use rubber gloves when etching. Other etchants and materials are mentioned below for the sake of compleness.
Acids. Strong acids react vigorously with almost anything they touch, including skin, eyes, lungs, and internal organs. Dilute nitric acid and Dutch mordant (hydrochloric acid plus potassium chlorate) have traditionally been used in etching. About nitric acid, the Center for Safety in the Arts (CSA) says: "Concentrated nitric acid is a strong oxidizing agent and can react explosively with other concentrated acids, solvents, etc. Nitric acid gives off various nitrogen oxide gases, including nitrogen dioxide which is a strong lung irritant [though odorless] and can cause emphysema. Large acute overexposures may cause pulmonary edema (chemical pneumonia), and chronic exposure may cause emphysema. During the etching process, flammable hydrogen gas is also produced.”
About Dutch mordant, the CSA says: “Mixing hydrochloric acid with potassium chlorate to make Dutch mordant produces highly toxic chlorine gas. Potassium chlorate is a key ingredient in many pyrotechnics, and is a potent oxidizing agent. It can react explosively with organic compounds, sulfur compounds, sulfuric acid or even dirt or clothing. On heating it can violently decompose to oxygen and potassium chloride. Storage and use are very dangerous and require special precautions especially when mixing.”
The 19th-century practitioners of photogravure introduced ferric chloride as an etchant. Because of its unique ability to seep through a permeable gelatin resist very gradually, ferric chloride was found to be ideal for the variable depth of etching required in photogravure. It is this variable depth of etch, controlled by the variable thickness of the gelatin resist, that makes possible the variety of tones in photogravure prints. The traditional acids generated excessive heat, bubbles, and were prone to foul-biting. Ferric chloride gives a more controllable etch, plus it is safer than the traditional acids. According to the CSA: "A safer substitute for etching copper plates is ferric chloride (iron perchloride). This forms acidic solutions so should be handled accordingly, but does not have the dangers of handling concentrated acids. Ferric chloride solution might cause minor skin irritation from prolonged contact."
Ferric chloride is actually a salt, not an acid. It is usually supplied in liquid form at 45- or 46-Baumé (a measure of concentration) and can be diluted to 42-Baumé (as measured by a hydrometer) for etching use. For soft-ground etching a dilution to 32-Baumé is good. Ferric chloride is a sort of warm rust color when fresh and gradually turns dull brownish-green after much use. I usually top up used solutions with fresh ferric chloride and discard the excess rather than discarding the whole thing. This keeps a constant etching strength while conserving resources and minimizing waste. Used solution can be safely neutralized with baking soda (sodium carbonate), which precipitates out the remaining iron. Ferric chloride corrodes even 'stainless' steel, so sinks and pipes have to be plastic.
Acetic acid (mixed with salt) is indispensable for brightening copperplates just before applying resist or etching grounds or ink to them. The mixture actually forms weak hydrochloric acid which lightly etches the surface, removing oxidation. Some people use vinegar or soy sauce instead of pure acetic acid, but the impurities complicate resist laydown in photogravure. A good working solution is eight parts water to one part each of acetic acid and salt by volume.
Alkalis. Sodium hydroxide (NaOH) is useful for cleaning and degreasing copperplates. Skin and eye contact with NaOH are dangerous, but it is not volatile. Rubber gloves are essential for mixing and using sodium hydroxide. Small quantities of sodium hydroxide can safely be poured down the drain, as it is the active ingredient in drain cleaner. Ammonia, sometimes used to adjust the pH balance of solutions, “is a skin irritant and highly toxic by inhalation. Ammonia is highly corrosive to the eyes. It has good odor-warning properties [it stinks].” Non-toxic alternatives for cleaning and degreasing copperplates include: <A> a slurry of magnesium carbonate and water, <B> baking soda (sodium carbonate), <C> various vegetable oils including ordinary salad oil, <D> Basic-H household cleanser from Shaklee, and <E> vegetable esters or vegetable cleaning agents (VCAs). These substitutes require more effort to remove etching ink, but are non-volatile and safe to use.
Organic Solvents. Organic solvents, used in cleaning up inks and etching grounds, are among the most common and insidious poisons found in the printmaking workshop. The effects of breathing the fumes of organic solvents such as benzene, toluene, xylene, turpentine, mineral spirits, methyl alcohol, gasoline, and others may be spread over years. Each bit of harmless-seeming exposure adds up to more likely illness. It is delusory to assume that if one has survived so far, all danger is past. Far from it! The odds of sickness and death increase with each whiff, which kills more cells. Cells die and are replaced all the time, of course, but the more often this happens, the more likely one of them will go awry and figure out how to evade the normal cell death routine. Having a survival advantage over normal cells, that cell will replicate more successfully and rapidly proliferate. That’s cancer.
According to the CSA: “High concentrations of most solvents can cause narcosis (dizziness, nausea, fatigue, loss of coordination, coma, etc.). Chronic occupational exposure to many solvents can cause permanent brain damage, with symptoms including loss of memory, behavioral changes, fatigue, spasticity, decreased intelligence, slower reflexes, poor hand-eye coordination, etc. Solvents can also attack other organ systems besides the nervous system. In particular, turpentine can damage the kidneys, toluene and chlorinated hydrocarbons can affect the liver, and methylene chloride can affect the heart. Lithotine, kerosene, and mineral spirits are skin and eye irritants and inhalation can cause intoxication and respiratory irritation.” Also: “Repeated or prolonged skin contact with solvents can cause defatting of the skin and resultant dermatitis (rashes, drying and cracking of skin, itching, etc.).”
For ink cleanup, Ad Stijnman recommends a European product called Vegetal Cleaning Agent, VCA, a compound of a vegetable oil and an alcohol. See Cleaning printing plates and brushes with VCA, by Sytze Folkertsma, Peter Sincovitz and Ad Stijnman, Printmaking Today, Vol. 5-1 (spring 1996). I have tried Vegetal Cleaning Agent (VCA) for etching ink cleanup on copperplates, and can report that it works better than anything else I have used. It removes all the ink from plates, rollers, and inking slabs in a completely non-toxic way. I have even used it to remove stopout varnish applied to a copperplate seven years previously -- no problem. VCA is non-volatile, with none of the toxic fumes that come from organic solvents. There is no reason to use organic solvents (such as benzene or turpentine) anymore.
If organic solvents are used, it is best to wear rubber or neoprene gloves and to have adequate ventilation. A good guide with installation examples is: Industrial Ventilation: A Manual of Recommended Practice (American Conference of Governmental Industrial Hygenists) 6500 Glenway Ave., Bldg D-7, Cinncinnati, Ohio 45211 USA).
Dusts and powders. These include rosin and asphaltum used in aquatinting copperplates, dry pigments for mixing ink, and various chemicals supplied in powder form. All of these are dangerous to breathe because the fine particles fill up the oxygen-carrying passages of the lungs, much like coal dust, asbestos, or tobacco smoke. Lung cancer and emphysema can result from repeated exposure. Recently (2011) a new material for aquatinting called Picco is available from Cape Fear Press. About rosin dust, the CSA says: “Rosin dust may cause asthma and allergic dermatitis. There is the hazard of explosion from the buildup of rosin dust, in enclosed rosin boxes, around an ignition source. Rosin dust (and asphaltum dust which is also sometimes used) is combustible. Sparks or static electricity have caused explosions in enclosed rosin and aquatint boxes”
Ventilation is recommended when working with dusts and powders, while taking care that strong air currents do not interfere with the aquatinting operation or spread dust throughout the workshop. For aquatinting, wearing a dust mask, then using strong exhaust ventilation after the asphaltum powder is adhered to the copperplate, is best. The mask always picks up a surprisingly large amount of dust that would have otherwise been inhaled. Dust masks are available from: Daniel Smith, 4130 First Avenue South, Seattle, Washington, USA 98134. New and better screens are being developed that can provide an effective substitute for aquatint dust grain.
Dichromates. Dichromated gelatin is the permeable resist that makes photogravure etching possible. The sensitizer which makes gelatin react to ultraviolet light is either potassium dichromate or ammonium dichromate. About ammonium dichromate, the CSA says: “Ammonium dichromate is a probable human carcinogen, is moderately toxic by skin contact, and may cause allergies, irritation, and external ulcers; it is highly flammable and a strong oxidizer.” Similar risks apply to potassium dichromate, though it is generally considered the less toxic of the two. These materials must be handled with rubber gloves, with care taken to avoid even the slightest skin contact or breathing of the powder. Liquid solutions are not volatile, however.
Ultraviolet (UV) light. Ultraviolet light activates the cross-linking of monomers into polymers in dichromated gelatin and other UV-sensitive materials, hardening them into an etching resist. Ultraviolet light also causes skin cancer and cataracts in the eyes. Carbon arcs are the most dangerous UV light sources. According to the CSA: “Carbon arcs produce hazardous metal fumes, and ozone and nitrogen dioxide (which can cause emphysema), and toxic carbon monoxide. Carbon monoxide is toxic because it displaces oxygen from the blood and deprives the brain and organs of oxygen.” With any exposed UV light source, blackout darkroom-type curtains around the light source are strongly recommended. In addition, UV safety glasses should be worn to prevent any light leaks from damaging the eyes.
From any manufacturer of UV light sources, it's useful to obtain test data on the actual spectrum their UV light sources emit, both the frequency range and the peak-energy frequencies. This is important not only for safety reasons, but also for energy-efficiency and and exposure-sharpness neasons. The fact is that no vacuum frame delivers a full vacuum throughout the entire exposure time, and so especially with large substrates there is always some loss of contact. The only way to minimize this is to minimize the exposure time. That's where the spectrum and peak-frequency data come in -- the more of the UV output that is concentrated in the range that your materials require, the sharper that image will be. A lot of UV light sources on the market are not only wasteful of energy and dangerous, but they also cause unnecessary losses of quality. Manufacturers should also supply data on corner-to-center ratio of light intensity. This is especially important for large images. The corners should receive at least 80 percent of the light intensity of the center.
Metal halide lamps, such as those made by Richmond Graphics, generate a narrower and more useable spectrum of UV, and are preferable for both exposure effectiveness and safety.
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