Copper Clay Success

14 Oct 2010

By Arlene Mornick

Copper and silver metal clay combined in a stunning pendant.

Help with Storing, Firing and Finishing This New Generation Metal Clay
I've loved working with silver metal clay for more than ten years now, and I particularly enjoy the opportunity to experiment with new 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.

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-

Knead the clay inside cling wrap.
Keep the clay wrapped in cling wrap inside an airtight container.
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.
* 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 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 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 to Remove Oxidation
As an alternative to pickling, use a butane 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. Allow the kiln to cool to 1500 degrees and remove the fired pieces from the kiln with tweezers or tongs and quench immediately 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.

Finishing
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 been successful the following schedule: fire to 1650 and hold for 2 hours, then quench as recommended above.

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.

ARLENE MORNICK is a Master Instructor for Art Clay World USA. She teaches at her home studio in Berkeley, CA ,and throughout the San Francisco bay area and at art shows throughout the country. You can contact her at Arlene@amcollection.biz.

Her "Mixed Metal Clay Earrings" project using copper and silver clays appears in the November, 2010, issue of Lapidary Journal Jewelry Artist.


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Comments

on 9 Jul 2013 11:18 AM

In the torch firing guidelines you say to set the timer when the piece starts to glow....but for how long?????

Thanks