Chasing pitch — known in many workshops simply as jeweller's pitch — is a thermoplastic compound used to support sheet metal during the allied techniques of repoussé and chasing. By providing a surface that is firm enough to resist lateral movement yet sufficiently yielding to absorb the repeated impact of hammer and punch, pitch allows a metalsmith to raise, depress, and define forms in sheet metal with a degree of control that no rigid backing material could offer. It is one of the oldest auxiliary materials in the goldsmith's craft, its use traceable through ancient Egyptian, Greek, and pre-Columbian metalworking traditions, and it remains in active use in contemporary studios and conservation workshops worldwide.

Composition and Traditional Recipes

In its most widely practised form, chasing pitch is a blend of three principal ingredients: pitch (typically Burgundy pitch, pine pitch, or bituminous pitch), plaster of Paris or whiting (calcium carbonate), and a plasticiser such as tallow or linseed oil. The pitch provides the thermoplastic matrix; the filler — plaster or whiting — adds body and controls hardness; and the tallow or oil modulates plasticity, preventing the cooled compound from becoming brittle.

Proportions are not fixed by any single authority and have always varied by workshop tradition, regional climate, and the specific demands of the work at hand. A mixture intended for use in a warm workshop or a tropical climate will carry a higher proportion of filler and less plasticiser to compensate for ambient softening; a recipe destined for a cold northern studio may be enriched with additional tallow to prevent the cooled pitch from cracking under the first hammer blow. This variability is not a deficiency of the material but a deliberate feature: the experienced metalsmith adjusts the recipe as a cook adjusts seasoning, calibrating the compound to the task.

Modern workshops sometimes substitute or supplement traditional ingredients with materials such as asphaltum (gilsonite), rosin, or commercially prepared pitch blocks, the latter sold pre-mixed and formulated for consistency. Some contemporary smiths experiment with synthetic thermoplastic compounds, though purists and conservators working on historical pieces tend to favour traditional formulations for their reversibility and their known interaction with historic alloys.

Physical Properties and Working Behaviour

At room temperature, properly formulated chasing pitch is a hard, slightly brittle solid, typically dark brown to black in colour. When gently heated — most commonly with a soft flame from a spirit lamp or a low-set torch — it softens progressively rather than melting sharply, passing through a range of plastic states before becoming pourable. This gradual transition is precisely what makes it useful: the smith can bring the surface to a tacky, plastic state without liquefying the entire mass.

The critical working property is the balance between resistance and compliance. When a punch is driven into the metal surface resting on pitch, the compound must resist hard enough to prevent the metal from simply sinking through, yet yield locally so that the hammer energy is absorbed rather than reflected back as a damaging rebound. A pitch that is too hard will crack and fail to support the work evenly; one that is too soft will allow the metal to sink and distort unpredictably. The ideal compound deforms slightly under each blow and then, over the seconds that follow, recovers partially — a behaviour that is, in rheological terms, viscoelastic.

The thermal mass of a well-filled pitch bowl or pitch block also plays a role: a large mass cools slowly and uniformly, giving the smith time to reposition the work or adjust the surface before the compound sets. Smaller pitch pans cool more quickly and may require more frequent reheating during a long chasing session.

Equipment: Pitch Bowls and Pitch Blocks

Chasing pitch is most commonly used in one of two forms of vessel. The pitch bowl — a heavy cast-iron hemisphere, typically 15 to 30 centimetres in diameter, resting on a leather ring or sand-filled leather pad — allows the smith to rotate and tilt the work freely in any direction, a significant advantage when chasing curved or complex forms. The bowl's weight keeps it stable under hammer blows while the leather or sand mount permits repositioning without lifting.

The pitch block is a flat or gently domed slab of set pitch, sometimes cast in a wooden tray, used primarily for flat or lightly curved work. It offers a larger working surface and is easier to prepare for beginners, though it lacks the rotational freedom of the bowl.

For very small or delicate work — fine jewellery chasing, for instance, as opposed to larger silversmithing — the pitch may be poured into a small tin, a wooden block with a hollowed recess, or even directly onto a steel plate, the choice dictated by the scale and geometry of the piece.

Working Method

The standard procedure begins with heating the pitch surface until it becomes soft and tacky. The metal sheet — annealed to maximum softness before any chasing session — is pressed firmly into the warm pitch, ensuring full contact across the area to be worked. Any air pockets beneath the metal will cause the sheet to flex and distort unpredictably under the hammer. The pitch is then allowed to cool completely before work begins; attempting to chase on warm pitch produces sluggish, imprecise results.

Once the pitch has set, the smith works with chasing punches and a chasing hammer, driving forms into or across the metal surface. The pitch absorbs each blow, supporting the metal from beneath while allowing controlled deformation. When the metal has been worked as far as possible in one position — or when it has work-hardened to the point where further hammering risks cracking — the piece is warmed gently from beneath or from the sides of the bowl until the pitch softens sufficiently to release the work. The metal is then lifted free, cleaned, annealed, and either returned to the pitch in a new orientation or flipped to work from the reverse side, as the repoussé technique requires.

Residual pitch adhering to the metal surface is removed with a suitable solvent. Historically, turpentine was the standard choice; contemporary workshops may use mineral spirits, acetone, or proprietary degreasing solvents. The metal is cleaned thoroughly before annealing, as burning pitch residue can contaminate the surface and, in some alloys, cause embrittlement.

Role in Repoussé and Chasing

The distinction between repoussé and chasing is one of direction: repoussé raises forms from the reverse of the sheet, pushing metal outward; chasing refines and defines those forms from the front, working the metal inward or laterally. Both operations depend on pitch support, but they make different demands of it. Repoussé, which involves larger punches and more forceful blows to move significant volumes of metal, benefits from a slightly softer pitch that yields generously. Chasing, which uses smaller, more precise punches to define line and texture, is better served by a firmer compound that provides crisp resistance against which fine detail can be articulated.

The interplay between the two techniques — and the repeated cycling of the work between pitch, annealing, and return to pitch — is what allows the metalsmith to build up complex, high-relief forms of the kind seen in ancient Greek toreutic work, Renaissance goldsmithing, and the elaborate repoussé panels of nineteenth-century presentation silver. In each case, the pitch is not merely a passive support but an active participant in the forming process, its properties shaping the character of the marks the smith can make.

Conservation and Historical Context

Because chasing pitch is thermoplastic and solvent-soluble, it is considered a reversible material in conservation terms — an important quality when the technique is applied to the repair or restoration of historical metalwork. Conservators working on ancient or antique pieces may analyse residues of original pitch compounds found in the interstices of chased work to characterise historical recipes, providing evidence of workshop practice and trade in raw materials across different periods and regions.

The longevity of pitch as a workshop material is itself significant. Few auxiliary materials in the metalsmith's repertoire have survived so unchanged from antiquity to the present day. The fundamental chemistry — a resinous or bituminous binder, a mineral filler, a fatty plasticiser — appears in workshop manuals from the Renaissance onwards and in descriptions of ancient practice reconstructed from tool marks and residue analysis. This continuity reflects not conservatism but the simple fact that the material works, and that no synthetic substitute has yet matched its combination of properties at comparable cost and ease of preparation.

Further Reading

• Gems & Gemology — GIA Publications
• Ganoksin: Chasing and Repoussé Techniques