Varathane

Varathane is a polyurethane wood sealant from Rust-Oleum. (Some long-time clayers and older websites may call it "Flecto" or "Flecto Varathane" in reference to its previous manufacturer.)

Though Varathane is not manufactured specifically for use on polymer clay, it is perhaps more commonly used (where it is available) than those products that were made for polymer clay. This is partly due to its unique qualities and partly because it is cheaper (per ounce) than the specialty products. It is very important to use only the water-based formulas of polyurethane with polymer clay. The oil-based formulas won't work.

Qualitites of Varathane

Available in different sheens: gloss, semi-gloss, and satin. Use the satin for a silky matte finish or the gloss for a glass-like shine.
Has a UV protectant and will not yellow.
Tends not the crack or peel, so long as it has been applied in thin coats and allowed to dry thoroughly between coats. (However, large expanses of some clays, especially Kato Polyclay, may be more difficult to cover in Varathane.)
When used to finish a thin, flexible piece that bends slightly, Varathane tends not to crack or peel as a result of the strain.
Can be diluted with water, either to thin it to the desired consistency for painting or dipping or to allow it to be sprayed on when brushing or dipping might disturb surface decoration.
Can be baked on for five to fifteen minutes at 250°F to speed drying and increase hardening of the coat. Curing in the oven bonds the Varathane to the polymer clay.
Can be reapplied for as many coats as desired.
Can be mixed with acrylic paints, inks, or colored powders (such as Pearl-Ex) to create custom stains and finishes.
Can be used to transfer images directly to clay.

If Varathane is not readily available, you may wish to try another water-based formula of polyurethane wood finish. Products that are compatible with clay will specify cleaning up with soap and water.

There are differing opinions as to how other brands compare to Varathane. Some are completely satisfied with their chosen brand and use it in all the ways that clayers use Varathane. Others are convinced that Varathane has superior strength or cite its UV protection as an added benefit. You can either try whatever you have on hand or can find locally or you can order Varathane on-line. If one product doesn't satisfy you, keep looking!

Examples

Varathane, from Rust-Oleum
http://www.rustoleum.com/brand.asp?frm_brand_id=21&SBL=1&slid=1

Water-Based Polycrylic Protective Finish, from Minwax
Available in three sheens, like Varathane.
http://www.minwax.com/products/protective/polycrylic.cfm

Kel-Thane II, from Kelly-Moore Paints
Available mostly in the Western U.S.
http://www.kellymoore.com/products/pwc_2096_series_kel_thane_ii

Availability

Try looking for Varathane and similar products anywhere that sells wood stains and sealants. Look in smaller hardware stores as well as the larger places. Varathane is also available on-line. These products usually come in gallon- and quart-size cans, but they are sometimes available in as small as a ½-pint can. A little goes a long way. To extend shelf-life and prevent contamination of your whole supply, don't work from the can. Instead, transfer a small amount of the finish to an "easy access" container and make sure that the can is tightly sealed and properly stored. Some suggest that store Varathane away from light, such as in a black film canister.