TLS can be found in some craft stores, near the solid polymer clay. Other brands of liquid clay may not be available in stores, but they can be ordered on-line.
Liquid Sculpey cures at 300°F in thin sheets. When cured, it is flexible and tough. Left untinted, TLS is translucent, but not completely clear. The texture of the cured TLS readily accepts pencil, ink, or layers of regular polymer clay (when the TLS is used to texturize a slick, non-receptive surface). TLS comes in a 2-oz. trial size, 8-fl.oz., 16-fl.oz., or 32-fl.oz. bottles.
Kato Clear Polyclay Medium (aka "Kato Sauce") starts out opaque, but clears as it cures. When hit with a heat gun (or in an oven with the temperature briefly bumped up), it clears even further, so that images or patterns beneath it are quite visible. It has a glossy surface when cured and can be sanded and buffed to a shine. Kato Polyclay Medium comes in 2-oz. and 8-oz. bottles.
Liquid Fimo (or Fimo Decorator Gel) is an extremely clear, odorless liquid clay. It starts off clear and stays that way during firing. It cures at 265°F to a very flexible, shiny sheet with a rubbery texture that is difficult to sand. Liquid Fimo comes in a 50-ml bottle.
Liquid Poly Glo is a glow-in-the-dark liquid clay available in six colors-- red, orange, green, aqua, blue, and violet. Liquid Poly Glo is available through Puffinalia, on-line.