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A touch of gold: mixing metals

Use 22-karat metal-clay slip to add a burst of gold to base-metal sheet.
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Try this technique with fine-silver metal-clay slip! The process is the same until the silver becomes liquid, and it coats the copper like solder.

You say the word “gold,” and most people think, “jewelry.” Gold rings, gold torques, a glowing array of solid gold wearable pieces. But there are different ways to create the look of solid gold or gold accents without the high cost, including gold plating, Korean keum boo, traditional gold leaf, fusing, and mercury gilding. (I’ve never tried mercury gilding, and for good reason — I want to live a few more years. It was outlawed in France in 1830.) Aura 22, a gold metal-clay slip, is a relatively new way to add gold to fine silver, sterling silver, and copper.

The technique of applying Aura 22 to copper is simple, uses no expensive or exotic equipment, and is safe. If applied and fired properly, the finished sheet can be etched, soldered, enameled, mill rolled, and fold formed. 

SUPPLIES

  • Copper: 16–24-gauge (1.3–0.5 mm), amount determined by design
  • Aura 22 with media or distilled water
  • Scouring pad
  • Paper towel
  • Rubber-tipped clay shaper
  • Mug warmer
  • Firebrick and broken charcoal blocks, or a new charcoal block
  • Tweezers
  • Candle
  • Torch
  • Quench bowl 
  • Pickle pot with pickle
  • Soft brass brush
  • Packing tape
  • Super pickle (hydrogen peroxide, sodium bisulfate)
INSTRUCTIONS
WHAT IS AURA 22?

Aura 22 is a mixture of 91.6% powdered 24k gold, 8.4% fine silver, and a water-based, nontoxic binder. When it’s fired, the alloy tests to 22k gold. One advantage of Aura 22 over traditional keum boo is that the gold is painted onto the metal, rather than burnished, allowing it to reach into recessed areas. 

NOTE: Aura 22 is a PMC product. Accent Gold for Silver is made by Jewelry Material Innovation, Inc. Accent Gold is 24k gold and can be torch-fired on sterling or fine silver; if using sterling silver, you first must raise the fine silver. 

PREPARATION
Prepare the copper. Use a scouring pad to clean both sides of a piece of copper (see “Size Limitations” BELOW), then rinse the metal in water. Water should sheet off the surface, not bead up. If it beads up, scrub the copper again. Use a paper towel to pat the copper dry, and handle it only by its edges from this point on. No greasy fingerprints! Set the copper aside.

Prepare the Aura 22. Open a package of Aura 22. Remove and carefully open the plastic jar. Depending on the orientation of the package during transport and storage, there might be an accumulation of gold and liquid binder in the cap. Use a rubber-tipped tool, such as a clay shaper, to scrape the excess material out of the cap and back into the jar. Carefully stir the mixture to mix the liquid binder and gold particles into a creamy consistency. If it’s dry, use the included media to reconstitute it. I’ve also used distilled water for this with no adverse effects.
Tip!

Size Limitations

For this technique, the flame needs to cover the entire surface of the metal to prevent oxygen from reach-ing the surface of the copper. Use the largest torch tip you have, and aim the flame at a firebrick to gauge how large of a piece of metal you can use based on how large the flame is. You can also use multiple torches for large pieces if you are comfortable holding a torch in each hand.

Apply the Aura 22. Use the rubber-tipped clay shaper to apply Aura 22 to the freshly cleaned copper [PHOTO 1]. I like to rub the tool back and forth to give the gold a natural edge. One coat is enough for sufficient coverage, but if you want a more dimensional look, apply a second coat after the first is dry.

Set the copper on a mug warmer until the Aura 22 is dry [PHOTO 2]. Yes, the manufacturer’s instructions say not to, but I’ve never noticed any difference whether it’s force-dried or air dried.

TIP: Let any excess Aura 22 on a rubber-tipped shaping tool dry there. Once it’s dry, peel it off and return it to the jar.

Mixing metals_photo 1
PHOTO 1
Mixing metals_photo 2
PHOTO 2
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PHOTO 3
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PHOTO 4

Prepare the firing surface. Aura 22 is meant to be applied to fine silver because fine silver doesn’t produce oxides when fired in a kiln or with a torch. When using it on copper, you must create a reducing atmosphere to prevent the copper from oxidizing and interfering with the gold’s ability to bond to it.

The most commonly available surface for this is a fresh charcoal block, but I like to use a spongy firebrick charged with charcoal. The center where I taught never had decent charcoal blocks, but we did have firebricks and lots of broken pieces of charcoal. To charge a firebrick, rub broken bits of charcoal over the entire surface of the firebrick.

Create the soot layer. Use tweezers to hold the copper piece gold-side down. Slowly pass the metal through a candle flame [PHOTO 3] until the surface is jet-black with soot [PHOTO 4]. Place the copper soot-side-up on the prepared firebrick. This setup, with the carbon-covered copper and firing surface covered with charcoal, will create a reduc-ing atmosphere in the next step.

Mixing metals_photo 5
PHOTO 5
Mixing metals_photo 6
PHOTO 6
FIRING

Fire the Aura 22. Light your torch (see “Choosing a Torch, BELOW”). Adjust the gas until you create a soft, bushy, flame with a bit of orange at the tip. If the flame blows out, relight the torch, and increase the amount of gas.

Your natural instinct will be to move the flame around as if you are soldering. Don’t! Come straight down on the copper. You’ll see the flame curl upward, making a curved, disk-like shape; this is called the corona [PHOTO 5], and it’s key to this technique. Once you commit, do not move the torch around. You want to fully cover the copper with the flame; any movement of the torch can expose parts of the copper to the air, which will cause oxides to form.

Now comes the part that’s like explain-ing how to ride a bike. Once you get it, you’ll get it, but you might topple a few times before getting it right. Watch what’s going on with the soot. Some areas will start to glow red, and the outline of your gold will start to appear. Wait two seconds after you see this, then pull the torch away for a split second and return it immediately. Hold the flame on the piece for longer than the length of time it was pulled away. Continue to pull the torch away and return it until all the soot has been burned away [PHOTO 6]. Turn off the torch. 

NOTE: The copper will look pretty bad at this point. It may look like areas of the Aura 22 were burned off, but don’t worry, they weren’t. If you did overheat the metal, the gold will have begun to alloy with the copper and pass into the surface, but have no fear — all is not lost. In my experience, it’s better to go too far with the heat than to underfire the piece.

Tip!

Choosing a Torch 

Use a torch that will let you lower the line pressure or control the amount of air mixing with gas. I like an acetylene torch, such as a Prest-o-Lite or Smith. When I teach where an acetylene tank isn’t allowed, I use the EZ (ORCA) Torch with MAP-Pro (a propylene/propane variant) fuel. One nice feature of the EZ Torch is the air-adjusting control ring on the torch head. It comes with three different-size tips; use the  largest. 

Mixing metals_photo 7
PHOTO 7

 

Quench the piece in water [PHOTO 7]. If any of the Aura 22 lifts from the surface of the copper, the piece was underfired. If this happens, clean the copper with super pickle, dry it, carefully lift up the Aura 22, and paint ad-ditional slip underneath it, like glue. Then, repeat the firing process.

FINISHING
Pickle the piece. Place the piece in regular hot pickle until the pickle begins to remove the oxides. Remove the piece from the pickle [PHOTO 8], rinse it, and gently brush it with a soft brass brush [PHOTO 9]. Place the piece back into the pickle, and leave it until the exposed copper looks pink with no dark spots or oxides. Remove the piece from the pickle, rinse it, and pat it dry.
Mixing metals_photo 8
PHOTO 8
Mixing metals_photo 9
PHOTO 9
Mixing metals_photo 10
PHOTO 10

Etch the copper. Apply packing tape to the back of the copper. Place the copper into super pickle. Within a few minutes, you’ll see small bubbles appear on the surface of the metal [PHOTO 10]. This is normal.

NOTE: Remember when I mentioned that overheating can cause the gold to alloy into the copper? This part of the process depletes the copper from the surface, leaving the Aura 22 exposed.

In under an hour, you’ll see a noticeable change in the color and surface of the ex-posed copper. Depending on the final use of your metal, you can stop at this point [PHOTO 11]. For a deeper etch, leave the piece in the super pickle overnight. Be care-ful though; a piece of copper will dissolve if left in this solution too long.

Remove the piece from the super pickle, then rinse and dry it. Your metal is now ready to be formed, soldered [PHOTO 12], sawn, drilled, enameled, or patinated without fear of the Aura 22 coming off.

Mixing metals_photo 11
PHOTO 11
Mixing metals_photo 12
PHOTO 12
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