Jewelers use so-called “oxidising” solutions to darken metals like silver, copper, brass, nickel silver, bronze and, with specialized mixtures, on gold. Metalsmiths patinate both large and small objects, as well as jewelry. We usually think of patinas as being green, but they come in many colors. There are also metal dyes which are very adhesive. Paints, epoxy resins and other materials are also used to darken recesses on work.
Metal coloring solutions are often made up of chemicals in toxic concentrations, so all chemical-lab precautions need to be taken with them. Many contain metal salts. Skin contact with patination solutions may cause dermatitis or in some rare cases, poisonings. Many patinas are toxic and corrosive. Fuming copper with ammonia, for instance, is a low-toxicity approach to obtaining blues and greens. These colors include copper hydroxides and copper chlorides, both dangerous for skin contact and if inhaled (as dry particles). Vinegar fuming will produce different copper salts. Any green or blue patination likely contains copper or nickel salts which are toxic and irritant.
If you are using patinas, you should make sure they are properly sealed when finished (I like to use transparent automotive enamel) and do not come in contact with food or skin; for instance, if making earrings, ensure that the surfaces against the skin are not patinated. Electric hazards are present if powered equipment is used and gas handling ones if torches are brought into play. Burns from hot surfaces or splashes of chemicals in the eyes. Some patina fumes attack the eyes. Metal being colored often has to be thoroughly degreased with the hazards attendant on degreasing methods and exposure to alkalis, acids and solvents.
The most commonly used darkening solution is liver of sulfur (potassium sulfide). It has some dangers associated with it. Skin contact should be avoided. It releases hydrogen sulfide gas when you use it, and really hazardous quantities of gas can be produced if it is brought into contact with an acid, as when some pickle remains inside a hollow jewelry object which is then colored with liver of sulfur solution. Hydrogen sulfide gas is considered rather dangerous. Long-term exposure to low levels may cause chronic lung disease (Stellman and Daum 161).
One author writes, “It is at least as poisonous as hydrogen cyanide” (Waldron 83). In any case, you should use gloves, tongs and good ventilation when using liver of sulfur solutions, and set up your workplace to avoid any chance of mixing such a solution with an acid. Many gun bluing chemicals containing selenium do not affect air quality when used cold (one shop was extensively tested to see how they did)-just don’t heat them. Jewelers also use selenic acid in proprietary metal- coloring solutions like Brass Black®. Sometimes jewelers use the selenium print toner that is used in photographic printing as a coloring agent. You should not touch, inhale or ingest selenium. Do not heat it.
Skin contact can result in serious contamination and selenium transfer right through the skin (Barbara Rockwell, Artmetal list, 3/29/07, “A public word of thanks”). Selenium exposure can cause eye irritation. Repeated exposure causes a garlic odor on the breath, metallic taste in the mouth, irritability, fatigue, dental cavities, upset stomach, loss of nails and hair (RTK). The chemicals used to clean metal before applying a patina can also be toxic (see “Cleaning Metals”). McCann’s list of substances not to use in patinas includes antimony, arsenic, cyanide and mercury compounds (AB! 443). Potassium dichromate “can cause irritation, allergies and skin ulcers” if you get it on your skin; inhaling it affects your nasal passages and lungs the same way-i.e.. it irritates them, and can cause ulceration. McCann warns that “dichromates are also probable human carcinogens” (AB! 446).
Burns, accidents, inhalation of dusts and particles, eye damage from chemicals, dermatitis.
Working heights, posture, reach are among ergonomic issues for patinating.
See “Fire Safety Rules” and “Fire Safety.” “Oxidizing agents, such as ammonium nitrate, concentrated hydrogen peroxide, potassium dichromate, and concentrated nitric acid, can react with solvents and other combustible materials to cause fires or explosions” (McCann, AB! 442). Beware those incompatible chemicals. Patination sealers may be flammable. Benzine (which is also “moderately toxic” through inhalation, skin absorption and ingestion) and lacquers (really bad if you inhale them, less so if absorbed through the skin) are also very flammable (McCann, AB! 442).
Absorption through skin, ingestion. Patinas can also be corrosive to eyes; I’ve been to hospital twice in my life for pitting of the eyeballs from nitric acid exposure during a cupric nitrate patination. Inhalation: some patinas may emit toxic gases when you heat them. McCann gives the example of potassium ferricyanide releasing hydrogen cyanide, and notes that sodium thiosulfate (that’s photo fixer) releases sulfur dioxide, which irritates the lungs (AB! 442).
In general, the simpler, the better; the fewer chemicals you use, the better. Wear protective clothing (including gloves and goggles) when handling anything caustic. Provide proper ventilation. Local Ventilation. Rossol warns against mixing chemicals for patination, “unless you understand fully the chemical reactions which will occur” (259).
McCann dislikes the practice of adding acids to sulfides for patination, “as described in some older literature,” as “this would cause the release of large amounts of extremely toxic hydrogen sulfide gas” (AB! 443). He goes on to say, “store oxidizing agents away from solvents and organic materials. Do not use them with techniques involving sawdust, wood shavings, or other organic materials, because of the risk of fire or explosion” (AB! 443). This is another instance of not mixing stuff that will combine in dangerous ways.
Artist Beware! recommends applying patinas by dipping or brushing, rather than spraying. If you must spray, use a spray booth (442). Dilute acid solutions are, of course, less hazardous than concentrated acids, so use the most dilute solution possible (and always add the acid to the water when diluting acids, never the reverse). McCann reminds his readers not to smoke, drink or eat in the studio, which is probably good advice all round (AB! 443). Use gloves, tongs, splash goggles and a fume hood with most coloring and patination solutions.
Avoid coloring metal with sulfides, and don’t use antimony, arsenic, cyanide or mercury compounds. Sometimes production jewelers use plastic resins and paints in the recesses of gold jewelry to provide an antiqued look and contrast for a design. Find out what materials are involved, and use gloves, glasses, ventilation and similar precautions when using them.
There are also now metal dyes available in many colors including reds and purples. If you use these dyes, obtain MSDS sheets for them, ventilate well, and wear gloves.
Note: There was a patination craze in the ’70s for decorative metalwork and I remember seeing a large metal bowl, like a fruit bowl, in a very famous department store in New York City. It was almost furry with powdery green patina; you could wipe your finger along it and coat it with the green patina powder. I was horrified.