Resin picture frames look like they would be hard to make, but in reality they are quite simple. Resin is a great medium to work with because it can be molded to create extremely beautiful and unique designs.
Make the mold for your resin frame. You should use the cardboard to construct a frame. Depending on how thick you want your frame, cut out strips of cardboard, say, 2 inches wide. Using your ruler, measure into these strips 1/2 inch. Using your ruler as a straight edge, place it on the 1/2 lines and bend the cardboard upward. Get as close to a right angle as possible. Do this until you have four troughs, two of one length and two of another.
Join the troughs at the corners. You will need to cut a tiny piece out of the inside edge of two of the troughs so that when they are taped together, you will have a fully connected rectangular trough. Use plenty of duct tape to hold the mold together with no cracks.
Spray non-stick cooking oil into the trough. Make sure, just like you would in a pot or a pan, to cover all sides up and down.
Pour in your resin, trying to get it as close to flush with the top as possible. The resin may need to dry for a day or so, so once poured, put it in an out-of-the-way place so it can dry.
Cut the duct tape holding the tops together. The resin frame should easily fall out. The outside will be oily from the cooking spray, so you should wash the frame in soapy water.
Smooth off any rough areas on the frame. Use the 100-grit sandpaper.
Paint your frame in any color you wish. Once it dries, you can tape a picture into the frame and even add a bit of cardboard to the back for extra stability if you wish.
You can buy artistic resin frame molds at many craft stores if you want a more elaborate mold than can be made with cardboard.
Work with resin in a well-ventilated area.