Help with Storing, Firing and Finishing This New Generation Metal Clay
I've loved working with silver metal clay for more than 14 years now, and I particularly enjoy the opportunity to experiment with new base-metal clays as they hit the market. Art Clay Copper, a new generation of copper clay, requires only 30 minutes of firing on an open kiln shelf for completion of a project.
|Knead the clay inside cling wrap.|
|Keep the clay wrapped in cling wrap inside an airtight container.|
The product is similar to the newer silver products (Low Fire Art Clay Silver and PMC3) in its basic forming steps: shaping, molding, carving, texturizing, drying, pre-finishing, and firing with resulting shrinkage (8-10%). There are some differences, and here you'll find helpful information in learning to use the newer copper clays.
When Oxidation Occurs
Unlike their silver counterparts, copper clay products are subject to oxidation, which may occur in three ways during use. Here are the conditions under which it occurs, and ways to minimize or avoid oxidation for each.
* Leaving unused clay uncovered and exposed to air: the exposed portion will form a black, hard surface. If this surface is very thick, cut it away with a craft knife until you see the original copper clay color. If the oxidation layer is very thin, you can use that portion of the clay by kneading the entire piece of clay until the copper clay color is consistent throughout the piece. Knead the clay inside of cling wrap and not with bare hands. To avoid oxidation of unused clay, keep the clay wrapped in layers of plastic wrap inside an airtight container and store in the refrigerator.
* Cooling of the piece immediately after firing: this oxidation is unavoidable, but if the piece is removed from the kiln with tweezers or tongs and quenched immediately with water, most of the oxidized layer will peel off. Exercise caution: the piece is extremely hot, so use heat-resistant gloves, and small chips of the oxidized layer may fly into the air, so use safety glasses. Oxidation that may be left on the piece after quenching may be easily removed with a steel brush. Persistent oxidation can be removed with pickle or heat from a torch.
* Long-term effects on the finished piece: a thin oxidation layer forms, which can be removed with a polishing cloth and, if necessary, metal-polishing chemical products.
Pickling to Remove Oxidation After Firing
After quenching and brushing fired pieces, place into pickling solution to remove the oxidized layer on the surface that results from firing. The amount of time the piece remains in the solution depends on the depth of the oxidation layer and may vary from 10 minutes to 2 hours.
Pickling solutions should be kept warm while in use. I use a very small crock pot. Its interior ceramic surface prevents any chemical reaction that may occur when using base metals with pickle.
When pickling is complete, neutralize the pieces with baking soda and water (1 teaspoon to 6 oz. of water).
Using a Butane Torch (Micro Torch) to Remove Oxidation
As an alternative to pickling, use a butane torch or micro torch. Hold the piece in a pair of locking tweezers, heat the piece to a red glow, and continue heat source until the black oxidation disappears and the copper begins to turn other colors, including variations of green and blue. Quickly quench. The black color caused by oxidation will be removed and the patina colors will remain.
Kiln Firing Guidelines
These firing instructions are specific to the new Art Clay Copper. Other low fire copper clays may have different firing instructions according to the manufacturer. The piece can be fired in a kiln at 1778 degrees.
Maintain this temperature for 30 minutes. Immediately remove the fired pieces from the kiln with tweezers or tongs and quench with water, which will help remove most of the post-firing oxidation layer.
Butane Torch Firing Guidelines
- Use a small butane gas torch to fire Art Clay Copper projects. I have had success with pieces that weigh 10 grams or less.
- Place the completely dry piece on a firing brick.
- Switch on the torch and direct the flame on the piece at a 45-degree angle from a height of about 2 inches.
- The flame should be rotated directly on the piece over the surface to heat evenly.
- Burning away of the non-toxic organic binder will produce a little smoke and flame.
- When the piece begins to glow red, start the timer.
- Continue to heat the piece for the recommended duration. Alter the distance of the torch from the piece to maintain the glow but not overheat the piece.
- I recommend the following firing times
– Clay volume of up to 5 grams: 5 minutes
– Clay volume of 6 to 10 grams: 8 minutes
Apply the same brushing and polishing techniques as with silver metal clay: steel brush, burnisher, tumbler.
Combining Copper and Silver
- Copper will sinter after 30 minutes at 1778 degrees and silver after 10 minutes at 1450 degrees.
- Copper melts at 1985 degrees and silver at 1760 degrees.
- Always fire copper components first to copper firing schedule; quench pieces as outlined above.
- The two metals do not sinter together. The already sintered copper piece and the still-soft silver clay are placed together so that they will lock together during a second firing at the silver firing schedule. Shrinkage of the silver clay during firing causes it to clasp and hold the copper piece.
- Quench piece after second firing.
- Clean piece with stainless steel brush.
- Pickle pieces as necessary.
- Finish with rotary drill, files, polish, as needed.
- Please note I have experimented with firing both clays together in one step. I have had some success the following schedule: Prefire at 1000 degrees on open shelf to burn out the binder, then fire in carbon with a ramp to 1500 and hold for 4 hours.
I use the same tools for both clays. Simply wipe the tool or work surface clean before switching clay types. The only tools that I am cautious about sharing between clays are my files.
About the author/designer:
"For me the simple elements of glass, light and heat when fused together create a special energy. That energy and spirit speak to me of passion and beauty, which inspire me to create colorful pieces of glass and silver art to wear, admire and enjoy. I am a metal clay, wirework and fused glass artist," Arlene says in her artist's statement. Arlene teaches in several locations in the San Francisco Bay Area. You can learn more about her via her website at www.LeMordesigns.com or contact her by email at arlene.mornick (at) yahoo (dot) com.
Arlene's "Mixed Metal Clay Earrings" project using copper and silver clays appears in the November, 2010, issue of Lapidary Journal Jewelry Artist.
Originally published October 14, 2010. Updated May 28, 2014.