"Finishing", or applying a polymer clay-friendly finish to your pieces, is strictly voluntary. Some pieces may need no finish at all. Generally, they are reserved for instances in which the artist desires a very shiny final product, as in faux lampwork beads.
While you can get a glassy finish on your clay from (diligently) sanding and buffing, there is another way. You can apply a finish to polymer clay to give it a glassy shine without all that sanding and buffing. Most finishes won't hide a bumpy surface, so you may still need to do a bit of light sanding, but many people find that if they're careful to smooth away fingerprints before curing, they can proceed straight to finishing after baking, with dazzling results.
Another reason to use a finish is to seal any surface treatment that might otherwise wear away. For instance, pieces antiqued with acrylic paint or decorated with mica powders may need to be sealed to protect the surface treatment. Anything with metallic rub-on waxes on it will need to be sealed if it's to be handled or worn, lest the waxes end up all over skin and clothes.
There are a number of finishes used by polymer clay artists. A few are manufactured specifically for use with polymer clay, while others have been "discovered" by artists to be compatible with the clay. Most are thin and work best when applied in two or three light coats (with ample drying time between each). Poly Glaze, on the other hand, is a dimensional glaze that is specially formulated to build up a thicker, glasslike coat-also through multiple applications, however. For general purposes, most polymer clay artists and hobbyists of the day are using water-based polyurethane finishes (such as Rust-Oleum's Varathane or Minwax's Polycrylic) or Future floor finish.
For more information about the different types of finishes typically used with polymer clay, visit our page on finishes.
Here are a few tips that may help you in your quest for the perfect, streak-free, bubble-free application:
- Rather than working from the can of Varathane (or similar finish), pour a smaller amount into an airtight container and refill that as needed. This will not only make it easier for you to open and close your bottle of finish, but it will also prevent contamination or drying out of a larger amount of the finish.
- Don't shake your bottle of finish right before applying it. This will only cause bubbles. Some suggest that you not even stir the bottle. However, note that if you are using semi-gloss/satin or matte finish, you may get a glossier finish if you don't shake or stir the bottle. The tiny particles that make the finish less glossy tend to settle over time, and if you don't redistribute them, there may be less of them near the top of the bottle.
- Use the softest brush you can find. A slightly more costly brush may be worth the price if it saves you the headache of bubbles. (That said, my best brush for applying finishes came from a set I bought for 50¢ at the closing of a dollar store!)
- Dip the tip of your paintbrush into the finish delicately and don't overload the brush. If you can avoid having to scrape your brush against the edge of the bottle (in order to remove excess finish, for instance), you'll also avoid some bubbles. For the same reason, you'll probably find that you have more bubbles when finishing an uneven-surfaced piece than one that is smooth, with no ridges or strong textural elements.
- Apply thin coats. Trying to increase coverage with thicker coats will only end up making a mess with dribbles and drops.
- On the other hand, you don't want too little finish on your brush, either. It flows on more smoothly if you have a thoroughly dampened brush. Experiment and you'll soon find what works best for you.
- After your final coat of finish has thoroughly dried, try popping the piece back into the oven for about ten minutes at 200°F or so. Some people find that this not only speeds up the curing process for the finish, but it also helps "melt away" faint stroke marks your brush may have left. (This works for faint stroke marks. Big, bold ones will not magically appear.) Some people report success with popping their pieces back into the oven after each individual coat has dried (i.e. between coats).
- If you're not having luck with brushes, take heart. Some people find success by dipping their pieces in Varathane or Future, then hanging them up to dry. (You will then need to go back and use a paper towel to wick away any drips that may be forming.) Others use small makeup sponges or even their fingers to dab on the finish. If one technique fails, don't hesitate to experiment with another until you find one that works for you.