Oil paint is slower drying than acrylic paint and can be a little more trouble to clean up, but it has special uses and abilities that are lacking in acrylic paint.
Unlike acrylics, which contain water that can cause bubbling if the paints are mixed into raw clay, oil paints can be mixed into uncured clay without ill effects-most of the time. (Keep reading; we'll get to that part in just a minute.) Oil paints can be used for most of the same purposes as acrylic paints, with one notable exception: Because oil paints take so long (at least six months) to dry completely, there's no sense in even trying to use them for crackling. (Stick to acrylics, leaf and foil for that.) Since it takes oils so long to dry, you shouldn't cover them with any sort of varnish, which will prevent them from ever drying thoroughly.
This slow-drying property of oil paints works in its favor for some techniques, so it's worth looking into the possibilities. Just be aware that different types of oil paints may not be equally compatible with polymer clay. Some oil paints may seem to dry (after curing), but actually disintegrate the clay later on.
Your best bet is to do one of the following things:
- Find out from someone with experience which brand(s) s/he uses. (At least one person I asked uses Windsor-Newton, a respected and widely available brand.)
- Look for oil paints that use a linseed oil base-not a petroleum base. Linseed-oil-based oil paints should be fine with polymer clay.
- Run your own tests, particularly if you already have a set of oils. Paint a small piece of cured clay with the oil paint and set it aside. If it remains tacky (sticky) for months, it's probably best to not use it on clay. If it dries, it should be ok for clay.
Below are a few ways to use oil paints with polymer clay:
- Paint with oils to add details or to color large areas of cured clay. Re-cure briefly to set the paint.
- Tint liquid clay with small amounts of oil paints to create opaque colors.
- Use oil paints to "antique" cured clay. Apply the paint, and then gently remove most of it. It will remain the crevices to create an aged appearance.
- Cover sheets of clay with oil paint and use in mokume gane.
- Oil paints are useful for some imitative techniques, such as faux agate slices and faux granite.
- Mix oil paints into raw polymer clay to create interesting marbled effects.