Metal Leaf

Just as the name implies, metal leaf is made of actual metal. It is possible to purchase real gold, silver, and copper leaf, as well as "composition leaf", which is made of cheaper metals that simulate the look of gold, silver, and copper. Imitation leaf also comes in variegated color patterns.

Most polymer clay hobbyists use the cheaper composition metals, but some people suggest that real gold and real silver have a better look. It's probably wise to practice with composition metal leaf before you decide to invest in pricier alternatives. Aluminum leaf, which mimics the look of silver leaf, has the added benefit that it should not tarnish the way that "the real thing" does.

Metal leaf is ultra thin and light-so light that the slightest puff of air can blow it away. Leaf usually comes in a booklet with sheets of tissue to separate the delicate pieces of leaf. Metal leaf adheres easily to the slight stickiness of raw polymer clay.

Possible uses for metal leaf

Crackling- Place leaf on a sheet of polymer clay. Roll sheet through the next thinnest setting on the pasta machine (or roll with a brayer or stretch by hand). While the clay stretches, the leaf cannot, so it breaks and forms a crackled pattern. You can continue to roll the sheet on thinner settings to create different looks. Turning the sheet before you feed it into the pasta machine again will also yield another style of crackle.
Patterned crackle- To obtain a specific pattern of crackle, put the leaf-covered sheet of clay through the pasta machine with a texture sheet or apply texture in some other way before further stretching the clay to produce more crackling.
Mokume gane- Adhere leaf to some (or all) of the sheets of clay in a mokume gane stack.
Surface application- Apply metal leaf to the surface of a polymer clay object before curing. Vary from partial to complete coverage, depending on the look you want.
Tint the leaf- Make whatever color metal leaf you want by hand-tinting it, once it's on the clay. (You can do this before or after crackling it and before or after curing the clay, depending on your project and preferences.) Use alcohol inks (like those from the Piñata or Adirondack line) for transparent color, which will allow the shine of the leaf to show though the color. For a different look, try Daler-Rowney Pearlescent Acrylic inks or a bit of acrylic paint.
Crackled backgrounds- Place a sheet of crackled leaf (or uncrackled, if you'd rather) behind a thin sheet of translucent clay. The leaf will show through the translucent clay. This is an especially effective technique to use with image transfers on translucent clay.
Faux Cloisonné Enamel- Put sheet of leaf over dimensional pieces of polymer clay to create leaf-lined cells. Fill cells with tinted, semi-translucent liquid clay. Leaf acts as reflective background for liquid clay "enamel" and uncovered lines of leaf mimic the wire in true cloisonné.

Tips for using metal leaf

Some metal leaf (real silver and copper and composition gold, for instance) is prone to tarnishing. Because polymer clay is such a new medium, and because there are so many variables at play, there are differing points of view on how best to prevent tarnished metal leaf. Most sources recommend that you seal anything including or covered in leaf, using any of the sealants that are safe to use on polymer clay. However, some artists insist that if you use aluminum leaf, tarnishing is not a problem and that it needn't be sealed. (Sealants may still be used to prevent exposed leaf from flaking off the piece.) The general consensus is that if the project is very special, you probably ought to use aluminum leaf (faux silver leaf) or real gold leaf, as they shouldn't give you problems with tarnish.
Avoid touching metal leaf during application, as the natural oils from your skin can increase the likelihood of tarnishing. Consider wearing gloves or using tweezers when handling leaf, or apply the leaf with a soft brush or other tool. It is also possible to place the sheet of clay on the leaf to minimize handling of the leaf itself.
If you have little bits of leftover leaf and don't care to piece it together to cover another sheet of clay, try mixing it into a little lightly tinted translucent clay. The speckles of metal leaf make ordinary clay sparkle. It's also great for some faux stones, such as lapis lazuli.

Examples

Mona Lisa Metal Leaf, from Houston Art-
This line of products includes both precious metal and composition metal leaf.
http://www.houstonart.com/metalleaf.asp

Magic Leaf, from LUCO-
Comes in a variety of colors and special variegated patterns. Also sold in flakes. Visit homepage (http://161.58.130.134/default.html ) to see listings of other products, including precious metal leaf, imitation leaf, and a selection of glitters and bronze and aluminum powders.
http://161.58.130.134/MagicLeaf.htm

Old World Art Gold Leaf, from Caldex Craft Products-
http://www.caldexcrafts.com/OldWorldArt.htm

Gildenglitz Gilding Leaf, from US Art Quest-
These flakes of metal leaf come in four colors.
http://www.usartquest.com/products/index.html

Stewart Superior Metal Leaf-
Available in six colors.
http://www.stewartsuperior.com/html/accessories.html

SEPP Metal Composition Leaf-
One source says that all of these products should be sealed to prevent tarnishing and that liquid polyacrylic sealants (typically used by many polymer clay artists) will also cause tarnishing. It may be wise to research this product further before purchasing for use with polymer clay.
http://www.seppleaf.com

Availability

Look for composition leaf at craft and art supply stores, where they are often located near the paints or glues. Composition and real metal leaf can also be purchased on-line.