Polymer clays all contain a basis of PVC and one or more of several kinds of liquid plasticizer.[1] Pigments may be added to the translucent base to create a variety of colors, along with small amounts of kaolin or white china clay or other opaquing agents where opacity is desired. Mica may be added to simulate pearlescent and metallic effects.
Original formulations of polymer clay remain soft until cured at
relatively low temperatures, but air-dry polymer clays have recently
been added to the market. Traditional polymer clay hardens by curing
at temperatures created in a typical home oven, generally at 265 to 275
°F (129 to 135 °C), for 15 minutes per 1/4" (6 mm) of thickness. The
clay shrinks inconsequentially when baked (about 1-2%), but does not
change texture. When properly conditioned and cured, most clays create
items that will not break if dropped or normally stressed. Cured pieces
may have additional layers or enhancements added and be re-cured with no
ill effect. As long as the maximum curing temperature is not exceeded,
there is no limit to the number of times a piece can be re-cured. After
it has cured, the clay surface can be left as is, sanded and buffed, or
finished with a water-based varnish.
Leading brands of polymer clay include Fimo; Sculpey, Premo and Studio by Sculpey, created by Polyform Products; Cernit; Formello; Modello; and Kato Polyclay.
Though the brands differ slightly in properties such as plasticity,
translucence, curing temperature, and flexibility when cured, most are
suited to a variety of applications. Specialty formulations include clay
that remains permanently flexible when cured, eraser clay, and
colorless and tinted liquid "clays" that can be used as slips, glazes,
and adhesives.
Polymer clay is available in many colors. "Special-effect" colors such as translucent, fluorescent, phosphorescent,
mica-containing "pearls" and "metallics," and variegated "stone" colors
containing contrasting fibers are also available. Standard colors,
which vary from brand to brand, can be mixed to create a virtually
infinite range of custom colors, gradient blends, and other effects.
Judith Skinner[3] is credited with inventing a technique that uses a pasta
machine to create consistent gradient-blended sheets of color. This
technique has many applications and is one of the basic skills developed
by hobbyists or artists in the medium.
Polymer clay can be colored with other media. Paint, ink, colored pencil, chalk, metallic or mica-containing powder, metal leaf
and foil, glitter, and embossing powder can be applied to the surface.
The same materials also can be mixed in as inclusions; this is often
done with translucent clay. When acrylic paint is cured onto the surface, it forms a permanent bond with the surface.
Few tools are essential for use with polymer clay, and these can
often be found around the house. The most widely used cutting tools are tissue blades, which are extremely thin and sharp, though craft knives and other blades can be used. A pasta machine is often used to create sheets of uniform thickness, to mix colors, to condition
the clay, and to create patterned sheets. A "clay gun" or extruder with
interchangeable die plates allows creation of lengths of clay in a
variety of uniform sizes and shapes. Most molding and modeling tools
used by traditional sculptors are suitable for polymer clay, but artists
often create improvised cutting, piercing, molding, and texturing tools
from items used in sewing, cooking, woodworking, and paper crafts.
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http://en.wikipedia.org/wiki/Polymer_clay
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