Goldsmithing: Pitch Options
Pitch is used all over the world by goldsmiths and silversmiths 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).
A pitch should grip adhesively onto the work when cool so the work does not chatter off easily. It should not shatter away under blows. Heat should percolate rapidly and smoothly through it so that it softens evenly, and not just a molten layer on top and hard a few millimeters down. Ideally it 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 it becomes a real burn hazard. You want to be able to heat pitch with a hair dryer or heat gun 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.
There are two basic kinds of pitch out there, an asphaltum based one (the usual in North America) and ‘real’ pitch, pine resin (for stickiness) mixed with a fat or grease (for elasticity) and a powder, flint, plaster, brickdust etc for resistance and body. 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.
You want a pitch to be easy to remove, either by chipping it off or by a simple solvent. To remove pitch I will heat up the metal slightly while still on the pitch, pushing upwards on an edge of the metal with a pair of tweezers while heating slowly. If you get this right the metal will come off the pitch suddenly with almost no pitch residues on it. I will then wipe off all of the remaining pitch I can get at with a rag (I keep orphaned socks around for this) or paper towel, reheating the metal slightly to keep the pitch soft while removing it.
Then you can remove the remnants with a large torch flame, making sure that you catch any smoke arising with the bushy flame to burn up the smoke as well. You need very good ventilation for this and I do not often use this method. Instead I prefer to take the metal and immerse it in a large sealed jar of methyl hydrate (solvent alcohol). Leave the metal alone to soak for ten minutes or so, then use a toothbrush to remove any pitch remnants (use gloves). The methyl hydrate works for resin based pitches, asphaltum/wax ones may need paint thinner instead.
I have yet to find a good pitch for chasing that is made in North American except that from Northwest Pitchworks in Seattle, where they make it themselves from pine resin and other traditional ingredients. Their medium pitch is pretty good, I find their soft far too soft for most applications and their hard melts so high that I consider it dangerous.
I normally order my own pitch in from the Fischer Company in Germany, a red forming pitch which up till now has been my favorite pitch of all, melts low, can be handled easily with the fingers, cools relatively hard. One can for instance make ‘snakes’ of it, rolled sticks that when cool become stiff pitch rods that can be fed into a small hole like into a vessel or a tube. Allcraft to my knowledge is the only company in North America that carries the same red pitch that I like.
Allcraft recently asked me to test and review a German black pitch they are importing, probably from Fischer. I approached it with some skepticism because I liked my red forming pitch so much. Well, after messing around with it for a while I must say I have now found a significant addition to my pitch options. It melts a little higher than the red pitch. It has a low melting temperature, but not enough to be dangerous. The heat transfers through it well and a hair dryer or heat gun could be used to soften it. It is handleable when soft and can be shaped and pressed into areas with the fingers (preferably dipped into water before touching it). It heated quickly and I could cool the metal stuck onto it and the pitch as well almost instantly by using a plant mister and spritzing it with water.
It is very hard when set, so hard that I could quickly stick a piece of silver sheet onto it, use a hammer and chisel to cut a long groove for scoring and bending and not have the metal push into the pitch anywhere while cutting the groove. This is pretty resilient stuff, good for slight forming, planishing, excellent for flat chasing, chiseling and engraving. It has an excellent grip, really superb adhesion. There was no way I could chip or pry my metal off the pitch.
This is a great pitch, perfect for certain jobs, fairly safe to use. It does things no other pitch does and it does them well. From now on I will have some of this in my studio.