The world of metal jewelry creation opened up dramatically with the advent of metal clay. While silver clay paved the way, bronze and copper metal clays have emerged as incredibly popular and accessible alternatives, offering warm tones and unique working properties for artisans and hobbyists alike. These materials behave much like traditional ceramic clay in their wet stage, allowing for shaping, texturing, and sculpting, but transform into solid, sintered metal after firing.
Understanding Bronze and Copper Metal Clay
At its core, metal clay, whether bronze or copper, is a fascinating composite material. It consists of microscopic particles of metal – either bronze (an alloy of copper and tin) or pure copper – mixed with a non-toxic organic binder and water. This blend creates a malleable, clay-like substance that can be worked by hand or with simple tools. The binder gives the clay its plasticity, holding the metal particles together during the creative process. The water content dictates the clay’s workability – too little makes it crumbly, too much makes it sticky. When fired in a kiln, the binder burns away completely, and the metal particles fuse (sinter) together, leaving behind a solid metal object that is remarkably dense and durable.
Properties: Bronze vs. Copper
While sharing the fundamental concept of metal clay, bronze and copper varieties have distinct characteristics that influence both the working process and the final result.
Bronze Metal Clay
Bronze clay typically yields a beautiful warm, golden-brown hue after firing and polishing, reminiscent of ancient artifacts. Since bronze is an alloy, its exact properties, including firing schedule and shrinkage rate, can vary significantly between different manufacturers. Some bronze clays require a two-step firing process or need to be buried in activated carbon during firing to prevent excessive oxidation and ensure proper sintering. Shrinkage rates generally range from 10% to over 20%, a crucial factor to consider during the design phase, especially for pieces needing precise dimensions or stone settings. Post-firing, bronze is strong and durable, suitable for various jewelry types.
Copper Metal Clay
Copper clay, made from pure copper particles, fires to the characteristic rich, reddish-brown color of copper. It’s often slightly easier to work with and fire than some bronze clays. Many copper clays can be fired in a single step, though some still benefit from being fired in activated carbon. Torch firing smaller copper pieces is sometimes possible, although kiln firing provides more consistent and reliable results, especially for larger or thicker items. Copper clay generally has a slightly lower shrinkage rate compared to many bronze clays, often around 10-15%. Post-firing, copper is quite malleable but also prone to oxidation, developing a natural patina over time, which can be a desirable aesthetic feature or something wearers might wish to prevent with sealants.
Verified Info: Always consult the manufacturer’s specific instructions for your chosen brand and type of bronze or copper clay. Firing schedules, shrinkage rates, and recommended firing methods can vary significantly. Following these guidelines is crucial for successful sintering.
Working Techniques: From Clay to Greenware
Working with bronze and copper metal clay involves several stages, each requiring specific techniques.
Handling and Preparation
Keep the clay moist while working. Use a bit of olive oil or natural balm on your hands and tools to prevent sticking. Store unused clay tightly wrapped in plastic wrap and inside an airtight container, possibly with a damp sponge (not touching the clay) to maintain humidity. If the clay starts to dry out while working, a tiny spritz of water can help, but avoid adding too much.
Shaping and Texturing
This is where creativity takes flight. You can:
- Roll the clay flat using non-stick sheets and acrylic rollers or slats for even thickness.
- Cut shapes using cutters, knives, or templates.
- Use texture mats, stamps, leaves, lace, or any object with an interesting surface to imprint patterns.
- Sculpt dimensionally by hand or using modeling tools.
- Use molds made from silicone or polymer clay.
Joining Elements
To connect pieces, you typically use ‘slip’ or paste. Slip is made by mixing a small amount of clay with water to create a thick paste. Apply slip to the areas being joined. Wet-to-wet joining is strongest. Wet-to-dry requires scoring both surfaces lightly and using slip. Dry-to-dry joining is also possible with careful application of slip or paste-type clay specifically designed for repairs and joining.
Drying
This is a critical stage. The clay piece must be completely bone-dry before firing. Any remaining moisture can turn to steam in the kiln and cause the piece to crack, blister, or even explode. Air drying works but can take time (24-48 hours or more depending on thickness and humidity). Speeding up drying using a food dehydrator, mug warmer, or placing the piece under a warm lamp is common. Check for dryness by placing the piece on a cool surface like glass or mirror; if moisture appears, it needs more drying time.
Refining the Greenware
‘Greenware’ refers to the bone-dry, unfired piece. This is the best stage for refining and smoothing. Use fine-grit sandpaper, sanding sponges, or emery boards to smooth edges, remove imperfections, and perfect the surface. Carving details is also possible at this stage. Remember that the dust contains metal particles and binder; work in a well-ventilated area or wear a dust mask.
Important Information: Ensuring your metal clay piece is absolutely bone-dry before firing cannot be overstated. Trapped moisture is a primary cause of firing failures. Take the extra time needed for thorough drying; it’s worth it to prevent disappointment.
The Firing Process: Transformation to Metal
Firing is the magical step where the organic binder burns away, and the metal particles fuse together (sinter) into a solid object. Kiln firing is the standard and most reliable method for both bronze and copper clays.
Kiln Firing Essentials
Most base metal clays (bronze and copper) require firing in an oxygen-deprived environment to prevent excessive oxidation, which hinders sintering. This is usually achieved by placing the dried greenware in a stainless steel firing pan filled with activated coconut carbon. The pieces are buried within the carbon.
Firing schedules involve ramping up the temperature to specific points and holding it there for designated times. Bronze clays often have complex schedules, sometimes involving two stages: a lower temperature hold to burn off the binder slowly, followed by a ramp up to the higher sintering temperature. Copper clays might have simpler, single-stage schedules. Again, manufacturer instructions are paramount here.
Digital kilns with programmable controllers are ideal for accuracy. Ensure your kiln can reach the required temperatures (often up to 900°C / 1650°F or higher for some formulas).
Torch Firing?
While some small, thin copper clay pieces *can* potentially be torch-fired using a butane torch, it is generally less reliable than kiln firing. Achieving the correct, even temperature for the necessary duration is difficult, and sintering may be incomplete. Torch firing bronze clay is generally not recommended due to its more complex firing requirements and susceptibility to oxidation.
Post-Firing Finishing: Revealing the Beauty
Fresh out of the kiln and cooled, the piece won’t look like shiny metal yet. It will likely be covered in a dark layer of oxidation or firescale and possibly embedded carbon dust.
Cleaning
The first step is cleaning. A brass or steel brush used vigorously will remove much of the surface oxidation. Tumbling the piece in a rotary tumbler with stainless steel shot and burnishing liquid is highly effective for cleaning, hardening, and bringing up an initial shine, especially for complex textures. Alternatively, pickling solutions (like commercial safety pickle, used warm in a crockpot) can chemically remove oxidation, but always follow safety protocols when handling acids.
Polishing and Shining
Once clean, the metal can be polished to the desired finish:
- Matte/Satin Finish: Achieved using abrasive pads (like Scotch-Brite) or fine-grit sandpaper.
- High Shine: Requires progressive sanding with finer and finer grits of polishing papers, followed by polishing compounds (like rouge) applied with buffs on a rotary tool (like a Dremel) or by hand with polishing cloths. Tumbling with steel shot also imparts a bright, burnished finish.
Patination
Patinas add color and depth, enhancing textures. Liver of Sulphur (LOS) is a common choice, creating shades from golden brown to deep blue-black on both copper and bronze. Apply the patina solution (following safety guidelines), then selectively remove it from high points using a polishing cloth or pad to create contrast and highlight details. Various commercial patinas are also available for different color effects.
Sealing
Sealing is optional. A microcrystalline wax polish (like Renaissance Wax) or clear lacquer can protect patinas and slow down natural oxidation, especially important for copper if the wearer wants to avoid the characteristic green skin discoloration some people experience.
Bronze and Copper Clay in Jewelry Making
These clays are incredibly versatile for creating unique jewelry pieces:
- Pendants and Charms: Ideal for showcasing textures, shapes, and patinas.
- Earrings: Relatively lightweight components can be made easily. Consider shrinkage for matching pairs.
- Beads: Hollow or solid beads add metallic elements to stringing projects.
- Ring Bands: Possible, but careful sizing considering shrinkage is essential. Strength is good but may be less than cast or fabricated rings.
- Setting Stones: Kiln-safe stones (some lab-created gems like CZs) can be embedded directly into the clay before firing. Natural stones usually require creating bezels or settings and adding the stone after firing.
- Mixed Media: Combine fired pieces with wirework, resin, enamels (low-fire), or other elements.
Choosing Your Clay
The choice between bronze and copper often comes down to:
- Color Preference: Warm gold/brown (bronze) vs. rich reddish-brown (copper).
- Firing Capability: Ensure your kiln setup matches the requirements of the chosen clay. Some bronzes need higher temperatures or longer/more complex schedules.
- Project Requirements: Consider shrinkage rate and final strength needed for the piece.
Cost is usually comparable between the two, although market prices for raw metals can cause slight fluctuations.
Bronze and copper metal clays offer a fantastic gateway into metalworking for jewelry artists. They blend the malleability of clay with the permanence and beauty of solid metal. While there’s a learning curve, particularly with firing, the ability to shape, texture, and refine metal by hand opens up endless creative possibilities, resulting in truly unique, handcrafted pieces with the warm allure of bronze and copper.
