Trade jewelers today use chasing and repousse rarely. Art jewelers and craft jewelers use it more often, and pioneered by Valentin Yotkov and others, there is a resurgance of interest at this time. Silversmiths use the techniques too, as do some engravers. Steel die makers (a rarity now) chase steel dies used for stamping out jewelry parts. An ancient system of working metals, this procedure uses steel punches to manipulate the metal while it is fixed onto a pitch or tar-like material. There are traditional pine-resin pitches and modern petroleum-based ones. The petroleum-based pitches are considered potential dermatitis-causing materials, as well as some evidence of their being carcinogenic. At this point most jewelers' pitches available through the main suppliers are petroleum-based, and thus, in my opinion, suspect. Besides, they don't work nearly as nicely as the pine pitches.
Hazards: Chemical hazards are present in fumes and skin contact with the pitch, particularly if it is a petroleum-based one. Noise is an issue. Chasers working on steel dies are exposed to machine oils and greases with their attendant dermatitis hazards, as well as to strong nitric acid in etching portions of the job. Ergonomic concerns are high as chasers might hit the tool several thousand times in a day. It is important to have the hammers carved so that one does not need to use the wrist while hammering-instead the hammer is held somewhat loosely and flops in the hand. Posture is important; take work breaks and a look at the ergonomic issues of doing the same thing all day. Solvents are sometimes used in pitch removal. If tools are not properly hardened and tempered they can snap. People have been blinded by such an incident. If the backs of the punches are not regularly ground back the mushroomed area can chip and embed in an eyeball or skin. Actually there are all kinds of eye hazards in this kind of work-I've splashed molten pitch into an eye before while helping someone pour some pitch. Hammer heads can fly off. Burns are an issue because you are working with hot materials. Spills of pitch that is too hot are a real danger-I've heard several bad stories. Removal of pitch from closed vessels when chasing is finished must be done very slowly and carefully to avoid an explosion with shrapnel and napalm-like pitch. Gas handling hazards are present if torches are used, electrical ones if you use heat guns and hair dryers to warm the pitch. Physical accidents of all kinds can happen-a careful workplace set-up is essential. Because chasers make many of their tools, the dangers found in "Hardening and Tempering" and "Blacksmithing" are involved as well. You are working with flammable materials of all kinds so fire hazards are present. Burning off pitch to remove it from metal creates dense, choking smoke.
Chemical: Petroleum tar-based pitches have been solidly linked to dermatitis reactions, and with lots of contact can create warts that are often the precursor to skin cancer (Carson et al, page 322). "Hot [petroleum-based] pitch is a skin irritant, and frequent and prolonged contact may cause skin cancer" (McCann, AB! 437). Fumes from overheated pine pitches may be irritating. Some people experience skin reactions to them as well. Burns are possible. Rosin, which is a major constituent of pine pitch, produces fumes which can cause asthma. These fumes can also irritate your eyes and lungs, and inhaling them constantly can cause chronic lung problems (McCann, AB! 459). Solvents used for cleaning metals and removing pitch may be an issue. Petroleum-based pitches are dissolved in paint thinner or mineral spirits, pine resin (colophony) based ones dissolve in methyl, ethyl or benzyl alcohol. Other more drastic solvents for pitch removal include benzine (VM&P naphtha, as opposed to benzene, which is a carcinogen, and should never be used for anything), acetone, toluene, lacquer thinner, kerosene. Layout dyes can affect you in chemical terms-read the MSDSs).
Physical: Sharp bits of tool or molten droplets of pitch can fly into your eyes. You can smack your knuckles with a hammer. Noise is an issue. Hearing damage can occur. You can cut yourself on chasing tools and sharp metal edges. CTDs are possible. Vibration injuries are conceivable.
Ergonomic: Chasing requires long periods of the same activity. Take work breaks every 45 minutes, do stretches, make sure your tools are correct, that a chasing hammer pivots between two fingers and is balanced so that you wrist and elbow do not have to move much at all to hammer, indeed some of the motion is transferred to the arm. The handle is not held rigidly when in use but flops up and down as the arm and writst and moved. Most chasing hammers require altering to obtain a better shape that does not stress the wrist in use. The weight of the hammer's head does the work in chasing, not the force of hammering. Check working heights and procedures.
Fire: See "Fire Safety Rules" and "Fire Safety." Pitches, rosins, and petroleum products are all flammable, especially when heated, which is what one does to manipulate it. Torches are often used for this. Benzine and other solvents used for pitch removal are flammable. "Heating pitch and the use of benzine to remove pitch from the metal creates fire hazards" (McCann, AB! 437).
Inhalation of chemicals, smokes and fumes, skin contact with materials, burns, physical dangers to eyes and body.
Safety precautions to use: Be very careful when using open flames around pitch. Store your solvents safely, and keep solvent-soaked rags away from heat sources. McCann suggests that you store them in "self-closing safety disposal cans that are removed at the end of each day" (AB! 437). Make sure there is adequate ventilation when burning off pitch. Wear gloves: keep pitch and benzine away from contact with skin. Be careful when handling tools. Wear your eye protection! Maintain your tools well, keep the mushrooming backs ground down, hammerheads tight and so on. Petroleum-based pitches will dissolve in mineral spirits, paint thinner, and VM&P naphtha. Pine resin ones dissolve in alcohols such as methyl alcohol. Avoid overheating pitches. Wear eye protection when working with pitch and chasing. Use less toxic layout dyes. Set up your workspace and procedures carefully and practice good housekeeping. Have good local ventilation for solvent use and hot pitch fumes. Keep a burn kit (and ice) around. Treat hot pitch as a very dangerous material. Avoid complacency.
Substitution options to reduce risk: Stick with a pine pitch and alcohols as a solvent. A wax like beeswax can substitute for pitch in certain broad chasing work. Consider using Aqua-plast and similar reheatable thermoplastics to replace some pitch use, such as holding jewelry while stonesetting. These plastics soften easily in hot water and are essentially what is used for plastic splints and casts in hospitals, so they should be fairly inert next to the skin. Use a heat gun or hair dryer to heat pitch instead of a torch flame (you may want hearing protection with these tools).
Note: If I look at my left arm, there is a patch about an inch and a half long by about an inch or so wide that has no freckles on it. Once upon a time, when I was quite young, I was hardening and tempering a series of chasing tools, and the quench was set up on the right hand side of the heating area. I had a very large torch, and proceeded to heat a tool and quench it by bringing my arm through the torch flame. This sort of studio set-up only happened once, and this was what convinced me, too, that rubbing vitamin E cream into the burn doesn't help it much in terms of recovery. The freckles are literally gone. Set up your workspace correctly.Further Notes on Pitch Use. Goldsmiths and silversmiths all over the world use pitch to hold metal in place while working it with hammers, punches or chisels. It should be hard enough to fill the requirements of the chasing work done on it. Most chasers will therefore have several hardnesses available: a soft one for deep forming, a medium for regular work and a hard for planishing on. In the old days, chasers would even have summer and winter formulations (which says something interesting about temperatures in their workshops). Goldsmiths use pitches to hold items for chasing, repoussée, drilling, chiseling, setting stones, as a filling in hollow knife handles on cutlery, in short, anywhere that metal has to be supported while being worked. Ideally, a pitch should be soft when warm but still handleable with fingers, so that one can easily push it into different metal shapes, mound it to hold an item and so on. If it melts or is soft only at high temperatures then it becomes a real burn hazard. You should heat pitch with a hair dryer or heat gun instead of a torch to keep away from the temperatures at which molten spatters of pitch can burn you severely-hence the desire to have a low-temperature warming pitch. If a pitch smokes or bubbles, it is far too hot and you need to be more patient in your heating. Use ventilation.
The biggest hazard is burns from pitch. Remember that the pitch should not ever bubble or smoke when heated. Pitch should not be heated until runny, as this is a very dangerous temperature. Wear safety glasses when working with hot pitch-I went to the hospital once with a splash of boiling pitch in my eye socket, burning my eyelid. I still have a strong memory of watching the small splash of pitch coming towards me from the bowl some feet away. Wear that eye protection when working with anything that can leap, spring, splash, fly into your eyes. If possible, work with the pitch at lower temperatures, softly heated so that you can actually manipulate it like a clay with your fingers without getting burned. The Fischer company in Germany and Allcraft in the United States both carry a red pitch I consider very safe for chasing and similar work. It can be shaped very comfortably with the fingers, and then the metal is momentarily heated to attach the pitch to it. Use ventilation when heating any form of pitch. There are two basic kinds of pitch out there: an asphaltum-based one (the usual in North America) and "real" pitch, made with pine resin (for stickiness) mixed with a fat or grease (for elasticity) and a fine powder, flint, plaster, brickdust etc. for resistance and body. Making your own pitch from resin, grease and powder has its own dangers: burns, fumes, silicosis from the very fine (200 mesh) powdered materials used. This degree of fineness drifts up into the air the moment the lid is off the container, and remember it is the particles you can't see that are the most dangerous. So, if mixing your own pitches, take special care about accident prevention, goggles, etc., and make sure that fumes and dusts are properly exhausted. As far as I can find, skin contact with pine resin pitch does not appear to be as much of a hazard (unless it is at the molten lava stage of course), though some people can get dermatitis from all kinds of things. Asphaltum-based pitch, however, is another story. This is one of the most common types of pitches that are available from tool suppliers in North America. There is plenty of evidence that petroleum-based materials like asphaltum can cause dermatitis, and, in cases of enormous exposure over time, skin cancer. Fumes can be very irritating to the eyes and skin, benzene (really, really bad) and hydrogen sulfide may be present, contained in those fumes (Stellman and Daum 201-202). If using home-made asphaltum (roofing tar) pitch, or asphaltum-based commercial pitches, use cotton gloves when in contact with it, use a non-greasy barrier cream, avoid as much skin contact as possible and consider switching to a higher-quality, pine-resin-based pitch (which has its own hazards). Petroleum-based pitches may cause dermatitis and skin cancer. Pine pitches (colophony) may sensitize skin. While some North Americans use shellac to hold items for engraving or setting I dislike shellac as being too brittle (and thus giving way at the wrong moment and endangering you) and possibly an organic irritant (shellac is, after all, a collected ooze from a kind of beetle).