A plastic picture frame doesn't have to look like plastic. Painting it can give it just about any look you desire to match a room's decor, such as metal, gloss black or even an antiqued white finish. The one caveat about repainting plastic is the type of paint definitely matters: Either the paint must be designed for plastic, or a special primer must be used first; otherwise, the paint won't adhere properly.
Picking the Paint
Spray paint gives the smoothest finish, but regular spray paint won't adhere to plastic. Since plastic isn't porous, traditional brush-on and spray-on paints aren't able to seep into the plastic, so they don't stick well. Choose a spray paint -- or a brush-on craft paint, if you prefer not to use a spray -- designed specifically for plastic. If you're unable to find a plastic paint in your desired color, a spray-on plastic primer may be used instead. Once the primer dries, regular paints may be used, offering a greater variety of colors than you may find in plastic-specific paints. If using a plastic primer, read the manufacturer's recommendations; some still recommend pairing the primer with specific types of paint, such as an enamel-based spray paint.
Preparing the Plastic
If the frame comes apart, remove the back and the glass. Gently sand the plastic with a fine-grit sanding block to scuff the surface slightly, which helps paint or primer adhere better. Wipe the frame down with a soft cloth to remove plastic particles. Tape off any areas you don't wish to paint to protect the surfaces while priming or painting.
Priming and Painting
Priming is only necessary if you are not working with a paint designed for plastics. Spray paint or craft paints specially designed for plastic do not require a primer. Set the piece atop newspaper or a tarp in a well-ventilated area such as outdoors. Ventilation is especially important with spray-based primers and paints, which may emit strong fumes. Shake the primer or spray can; then prime or paint the frame while holding the can 12 to 18 inches away from it. Begin each spray burst slightly before the beginning of the frame and end it after the edge of the frame to help prevent drips and blobs. Allow the primer to dry before painting with your chosen paint. Allow paint to dry between coats as well.
Once the frame is painted its basic color, jazz it up even more with stamps, painted designs or rubbed-on color. Use acrylic craft paint on rubber stamps to stamp on designs. Create your own stencils out of contact paper, cutting out designs, or use pre-made stencils for designs such as vines or stars. Rub on acrylic paint or tinted glaze to add an antiqued appearance, such as a slightly gray or honey color over a pastel frame. Add an elegant touch by rubbing gold or silver glaze over a black frame, brushing paint on with a foam brush, then rubbing most of it off with a soft cloth.