How Long Does It Take To Fire Copper Clay?

What is Copper Clay?

Copper clay is a specialized modeling and sculpting material that contains pure copper metal particles. It has aclay-like texture that can be easily shaped and molded when soft. When fired at high temperatures, the clay transforms into solid pure copper metal.

Copper clay is made from a mix of copper metal powder, an organic binder and water. The binder acts like glue to hold the copper particles together in a pliable form that can be manipulated like clay. Common binders used include plant-based materials like cellulose or lignin.

The main use of copper clay is to create jewelry, beads, pendants, charms, decorative objects and small sculptures. The soft pliable clay can be hand-molded into detailed designs, then fired to convert into a solid copper piece of jewelry or art. Copper has an attractive reddish-orange color when fired. The finished copper pieces can also be colored, textured, polished, patinated or embellished.

Copper clay allows artists, crafters and jewelry makers to design pure copper pieces without needing special metalworking skills. It offers the shaping ease of clay along with the beauty and durability of solid copper metal after firing.

Firing Process for Copper Clay

The firing process for copper clay involves slowly heating up the clay piece to a high temperature, holding it at that temperature for a duration of time, and then allowing it to slowly cool back down. This process bonds the fine copper particles in the clay together into a solid metal piece through a sintering process. Here are the key steps involved in properly firing copper clay:

1. Place the dried unfired copper clay piece on a fired clay kiln shelf or proper firing surface. Make sure the piece is not touching anything else.

2. Program the kiln with the proper ramp up rate, target temperature, hold time, and ramp down rate. A typical program would be ramping up at 300°F per hour to 1600°F, holding for 2 hours, then cooling at 600°F per hour.

3. Close the kiln and start the firing program. Monitor the kiln to ensure it is following the program properly.

4. Once the firing cycle is complete, allow the kiln to cool completely before opening the door and removing the fired piece.

5. Optional – If desired, tumble polish or sand the sintered copper piece. Then clean it and apply a patina as desired.

Following this full firing process ensures the copper clay is fully sintered into solid pure copper metal. Taking shortcuts or improper firing can lead to weak, porous results.

Importance of Proper Firing

Properly firing copper clay is crucial to achieving a high quality finished piece. Underfiring or overfiring copper clay can lead to a variety of issues that negatively impact the end result.

Underfiring occurs when the clay is not fired at a high enough temperature or for an adequate length of time. The clay will not fully sinter and bond, leaving it weak and prone to breakage. Pieces may crumble apart if underfired. The metal will also not fully fuse, leading to a rough, porous surface texture instead of a smooth shiny finish. Underfired clay is also vulnerable to tarnishing.

Overfiring happens when firing at excessively high temperatures or for too long. This can cause the clay to melt, slump, or burn, destroying the original shape of the piece. Overfiring leads to a loss of fine details and textures. It also makes the metal too brittle, resulting in cracks or breakage. Overfired copper develops a burnt reddish hue rather than the desired warm golden tones.

Firing at the proper temperature and duration is key to creating durable jewelry or art pieces in copper clay. It enables full sintering and metal fusion while avoiding deformation, breakage, porosity, and other firing defects. With careful firing, the stunning colors and luster of copper can be brought out in finished clay pieces.

Firing Temperatures

Copper clay must be fired according to precise temperatures to achieve the desired results. The recommended firing temperature range for copper clay is between 1,400-1,600°F (760-871°C). Firing at lower temperatures may result in the binder not being fully burned out, leaving organic residues in the metal. Higher temperatures can start to melt the copper particles, causing distortion or holes.

Most clays fire optimally around 1,500°F (815°C), which allows the binder to be completely removed while avoiding any melting of the copper metal. 1,500°F is generally considered the ideal temperature for firing copper clay while still providing some wiggle room in either direction.

Firing temperatures may need to be adjusted based on factors like clay thickness. Thicker pieces may require slightly higher temperatures or longer hold times to fully burn off the binder. The ramp up and cool down rates can also impact results, with slower rates recommended for thicker or more detailed pieces.

Having an accurate kiln with a working thermocouple is important for achieving proper firing temperatures for copper clay. Monitoring the temperature and making any necessary adjustments during the firing process can help prevent under- or over-firing the metal clay.

Firing Duration

The ideal firing duration for copper clay depends primarily on the thickness of your piece. Thinner pieces require less time in the kiln compared to thicker sculptures or components. As a general guideline:

• Pieces under 3mm thick: 30-45 minutes
• Pieces 3-6mm thick: 45-60 minutes
• Pieces over 6mm thick: 60-90+ minutes

You’ll need to experiment to determine the optimal firing times for your specific clay thickness and kiln model. It’s always best to start on the low end (30-45 minutes) and refire if needed. Overfiring can cause oxidation or other issues. Using a kiln sitter can also help automate optimal firing times.

The most important thing is bringing the kiln up to the proper copper clay firing temperature (around 1,650°F). So firing duration correlates with how quickly your kiln reaches peak temperature. Rapid kilns may only need 30-60 minutes at top temperatures, while slower kilns may require an hour or more of sustained high heat. Watch for visible glowing/red heat in the kiln chamber to gauge when proper firing temperature has been reached.

Ramp Up and Cool Down Times

Proper ramp up and cool down times are crucial for successfully firing copper clay. Ramping up too quickly can cause cracks or explosions. Cooling down too quickly leads to weak, crumbly pieces.

For most copper clays, aim to ramp up around 100-150°F per hour until reaching peak temperature. For example, if firing to 1,600°F, ramping up at 150°F per hour would take around 10-11 hours to fully reach temperature.

Cooling down is just as important. Let pieces cool slowly inside a turned off kiln. Cooling at around 200°F per hour is recommended. For a peak temperature of 1,600°F, cooling down at 200°F per hour would take around 8 hours.

Having proper ramp up and cool down times, usually 18-20 hours total, ensures the binders burn out slowly and the copper particles sinter together correctly. Rushing the process risks weak or damaged finished pieces.

Firing Tips

Here are some helpful tips for firing copper clay properly:

• Allow pieces to dry thoroughly before firing. Moisture can cause cracking or even explosions.
• Support pieces with kiln posts, stilts, or firing ramps to prevent sagging.
• Place pieces with sufficient space between them so they don’t fuse together.
• Use kiln paper or fiber blanket beneath pieces to prevent kiln shelf marks.
• Program the kiln with a long cooling cycle to prevent cracks from thermal shock.
• Always use adequate ventilation when firing copper clay.
• Wear a respirator mask to avoid breathing fumes during firing.
• Quench non-enameled pieces immediately after firing to maximize hardness.
• Firing too hot can cause melting, blistering, or burnout.
• Firing too cool can result in weak, brittle pieces.

Following proper firing procedures helps ensure copper clay pieces turn out as intended. Pay close attention to recommended temperatures, hold times, and ramp rates.

Firing Equipment

The most common equipment used to fire copper clay is a kiln. Kilns allow for precise temperature control and even heating throughout the firing process. There are several types of kilns that can be used:

• Electric kilns – These kilns use electricity to generate heat and typically allow you to program precise ramp up, hold, and ramp down times and temperatures.
• Gas kilns – Gas fired kilns use propane or natural gas as the heat source. While temperature can be controlled, they do not offer the precision of electric kilns.
• Torch kilns – Small tabletop kilns designed specifically for firing small jewelry pieces. They heat up and cool down quickly.

Other firing equipment options include:

• Handheld butane torches – Allow for direct, focused heating but can be more difficult to control the temperature.
• Burnout ovens – Small ovens designed to slowly pre-heat metal clay pieces before firing with a torch.
• Soldering torches – Can generate enough heat to fire small pieces, but temperature control is difficult.

The type of firing equipment used will depend on factors like the size and number of pieces being fired, desired control over temperature and ramp times, budget, and availability of equipment. Kilns offer the best results, but torches can also be effective with practice.

Troubleshooting Firing Issues

Firing copper clay can sometimes result in issues if not done properly. Here are some of the most common problems that can occur, and tips on how to avoid them:

Bubbles or Blisters

If bubbles or blisters form on the surface of the fired piece, it is likely a sign that the clay was fired too quickly and the organic binder burned off before the copper particles could fuse together smoothly. To prevent bubbles, heat the kiln slowly and allow plenty of hold time at peak temperature.

Firing Cracks

Cracks can happen if copper clay is allowed to dry out too much before firing. To avoid cracks, keep the clay workable and fire soon after drying is complete. Cracking can also occur from thermal shock if the kiln cools too rapidly after firing.

Incomplete Fusion

If the clay does not become fully fused and metallic in appearance, the cause is usually insufficient heat or too short of a firing time. Make sure to fire at the proper high kiln temperatures and hold at peak temp long enough for full fusion, usually at least 2 hours.

Warping or Shrinkage

Improper drying or firing too rapidly can cause uneven shrinkage that leads to warping. Allow clay pieces to dry slowly and evenly. During firing, use gradual ramp rates and extended hold times at peak temperature to ensure clay has time to shrink uniformly.

By carefully following recommended time and temperature guidelines, as well as proper drying and firing procedures, many common issues with copper clay can be avoided.

Firing Copper Clay Safely

When firing copper clay, safety should always be your top priority. Copper clay releases fumes during the firing process that can be harmful if inhaled. Proper protective equipment and ventilation are essential.

Use a ventilated kiln or fire outside using a torch. Never fire copper clay indoors without proper ventilation as toxic fumes can build up. Wear an N95 mask to avoid breathing in fumes. Use heat resistant gloves when torch firing. Tie back long hair and avoid wearing loose clothing that could catch fire.

Have a fire extinguisher on hand whenever torch firing. Be aware of flammable materials nearby that could ignite. Do not leave a kiln or torch firing unattended. Fumes are most concentrated when cooling down; ventilate for at least an hour after firing.

Clean kiln shelves after each firing to prevent buildup of copper residue. Dispose of firing debris properly. Wash hands thoroughly after firing. With proper safety precautions, you can enjoy firing copper clay and reap the benefits of this versatile material.