You can use polymer clay without any special finishing treatment at all. The finish of polymer clay right after firing varies by brand - Fimo has a slight gloss, Sculpey has a matte finish, Cernit is slightly waxy-looking. For many pieces, you may find that the clay's natural finish best enhances the effect you want. For other pieces, you may prefer the shinier or glossier finish available with various finishing techniques such as wet-sanding, buffing, and glazing. Buffing produces a deeper, more subtle sheen; glazing produces a harder shine and takes considerably less time.

Sanding polymer clay is best done under water - either under the tap or in a basin. Use wet/dry sandpaper, starting with a grit of about 400 and progressing to at least 600. Sand each surface a few strokes with each grit of paper. When done, wipe off the piece and let it dry.

You can buff by hand with a clean soft cloth (terrycloth, t-shirt, or the pique knit used for polo shirts) by vigorously rubbing the piece for several minutes to bring out the shine. You can also use an electric buffer with a cloth or muslin wheel. If you use a power buffer, be sure to keep the clay moving while you buff, and hold it lightly against the wheel; pressing can cause gouges in the clay. (You can buff polymer clay without sanding it smooth first, but the shine you obtain will not be as great.)

For an alternative to heavy buffing use the fine steel wool made for wood finishing. Lightly rub the sanded clay with the steel wool, then hand-buff briefly, to bring out a bit of subtle shine.

Elise Winters has experimented with various techniques for polishing polymer clay in a tumbler. Her original article in the April/May 1996 issue of Lapidary Journal described using small bits of wet/dry sandpaper along with the beads to be polished; the sandpaper bits take the place of the grit normally used in a tumbler.

Later, she found a special polishing paper that gives superior results and can be used either in bits like sandpaper (for irregular pieces) or to line the inner surface of the tumbler (for beads). An article in the March/April 1997 issue of Jewelry Crafts describes this method. If you'd like to try this method, the special papers are available from Rio Grande, on page 374 A of their 2001 Tools & Equipment catalog (3M Tri-M-Ite Polishing Paper).

Several manufacturers of polymer clays also make gloss and matte glazes. These are brush-on finishes that dry in about an hour. Some glazes are water-based; try to avoid these, since they have a tendency to peel over time, particularly in jewelry or other pieces that have to withstand a lot of friction.

Another glaze that can be used is Future floor polish. This is actually an acrylic coating that works well on polymer clay. It is very thin, so to get the best shine, you need to sand and buff your pieces smooth before using it. When used on unsanded clay, it produces a finish more like matte glaze. You can also dip pieces in Future for a heavily-coated, very shiny look. (Be careful to rotate the piece back and forth a few times after dipping to get rid of the excess.)

Many clay artists have also successfully used Flecto Varathane Elite Diamond Finish. This is a lacquer found in hardware stores, in the area with the wood stains and finishes. It comes in satin (matte), semi-gloss, and gloss finishes. A piece with Flecto on it can be re-fired for a stronger glaze. Flecto will also bend and flex without peeling - an important consideration if you're using a flexible clay in thin sheets.

Both Flecto and Future are much less expensive in quantity than the polymer-clay manufacturers' glazes. Since they come in large containers, you may want to put some into a smaller container for your workspace to make it more manageable.

Do not use nail polish to lacquer your clay, and be careful about using other glazes. Many lacquers - including most nail polish - will react with the clay over time, causing it to turn sticky. Some glazes, especially spray-ons, never dry properly when used on polymer clay. If you want to try a new glaze, make sure to test it first.

The easiest way to glaze a bead is to stick it on a toothpick or skewer. Hold the bead by the toothpick to paint on the glaze, then stick the end of the toothpick into a block of styrofoam to let the glaze dry.

Polymer clay as it comes out of the oven has an attractive matte finish. If you want a little more shine, but still a subtle effect, you can rub the piece lightly with fine steel wool, then buff it with a cloth to bring out a bit of shine. Some of the clay manufacturers also make matte glazes, which are less shiny than the gloss types, but bring out the colors of the clay a bit.

You can sand away small flaws in your finished pieces with 320 or 400 grit sandpaper. Make sure not to press too hard, and check your piece frequently, to avoid sanding through a veneer or creating a flat spot. When you're through, you can restore the sheen of the sanded area by sanding it gently with a finer grit of paper, then lightly buffing the piece all over or using a matte glaze.

Some glazes react badly with the polymer clay. Either they never completely dry, leaving a sticky surface that attracts dust and lint, or they seem to dry but get soft and sticky months or years later. You can avoid this problem by sticking with the glazes made by the polymer clay manufacturers, or other glazes that you've experimented with and know to work with clay. (Remember when experimenting that problem glazes sometimes seem fine for months before they start reacting with the clay.)

Once this has happened to a piece, not much can be done to salvage it. You can try placing the piece in a low oven (200-250° Fahrenheit) for an hour or so; this sometimes sets a gummy glaze.