You can paint plastic in the mold, save time and materials and get better results than painting castings separately.

A quick demonstration of in-mold painting: epoxy resin cast into a plastic butter-tub lid. The resin picks up the painted image completely.

You can apply surface color to castings made from any liquid plastic resin such as Polyester, Epoxy, or Polyurethane Plastic at the same time you make the casting.

It is best to use a rubber mold for this technique. Polyurethane molds are preferred - they won't be harmed by spray paint, and the paint can be evenly applied to the mold. Silicone molds will also work, but since Silicone repels some types of paints, you may not get an even coat. Latex rubber molds will work, but the solvents in some spray paints may damage the mold.

It's extremely easy - simply spray paint your mold with the color of your choice before you pour in the liquid casting resin. You can use acrylic or oil base spray paints. Do not use a release agent - in most cases the spray paint will also act as a release agent. (You can also apply paint with a brush or even a rubber stamp if you prefer).

Let the paint dry, and then mix and pour the liquid resin as usual. As the resin cures, the paint on the surface of the mold will actually become part of the surface layer of your plastic casting.

When the plastic has cured, remove it from the mold. The surface layer of the casting will be the color of the paint.

If you want to test this technique and see how well it works before actually using one of your molds, try this:

Get a plastic lid from a grocery product that has a colorful design on it. Lids from butter tubs are ideal. (The lid should NOT be made from styrene if you are using polyester resin.) Mix and pour the plastic resin of your choice over the colored design. Let the resin set, and then peel the cured plastic off the lid. The result will be a plastic casting with a high quality reversed image of the design embedded in the surface. Rub over the design with your fingernail and you will see it is much more durable than any type of painting would be.

You can make designs like this by painting, silk screening, or rubber stamping images onto the surface of your mold, before pouring the plastic resin. You can also use inkjet or laser-printed images - see this technique.

There are several advantages to in-mold painting:

1) The color layer in your casting will be very durable - it has actually become part of the plastic. It is much more durable than it would be if you cast the product and then painted it.

2) If you had previously been coloring your entire batch of plastic resin with color pigments, you will save a lot of money. By spray painting the mold, you only color the top layer of the casting, not the entire casting.

3) The finished casting will appear to have a very even coat of color, even if you didn't paint the mold evenly.

4) You can also decorate the surface with other materials, using similar techniques. Try spraying a mold with a clear acrylic spray and then immediately dusting it with glitter or fine sand, for instance. The surface of your finished casting will include the glitter or sand.

5) You can use spray paints such as "chrome" or "brass" paints to get the look of metal. Or use the new "granite" or "marble" spray paints to get those effects.

Download a PDF source list

Includes 26 suppliers of all mold making and casting materials mentioned in ALL the demonstrations on this web site, including silicone rubber, polyurethane rubber, latex rubber, polyurethane plastic, epoxy resin, polyester resin, molding clay, foam board, release agents, pottery plaster, Hydrocal, metal powders, other plastic resin fillers, and gelatin molding compound. With company names, addresses, phone numbers, and web sites. Downloads to your computer as a PDF file.

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