Measure your painting. Add at least four inches to the width and length measurements to determine the size of your mat. Alternatively, choose a standard size ready-made frame at least two inches larger than the painting on all sides, and size the mat to fit. Choose a backing board the same size as your mat's outside measurement.
Cut the mat. If your painting is a standard size, you may be able to purchase a precut mat. If your painting is an unusual size, you will need to measure and cut your mat using a professional mat cutter, or have a mat cut for you. Be very careful–you can cut each mat only once. Mat openings should be at least 1/4 inch smaller on each side than the painting itself. This prevents the paper edges from showing.
Attach the mat to the backing board with archival tape using standard hinge construction. Place a single smooth strip of tape all along the inside of the join between the two boards. This tape acts as a hinge, keeping the boards connected while still allowing them to change shape and size with differing moisture levels. You can reinforce the ends with smaller strips if peeling tape is a concern. Do not tape the boards together on the outside, or connect them on all edges. These methods are less professional and can cause problems in years to come.
Remember to check the positioning of the mat and backing board to avoid a crooked mat. Use the same method of hinge construction to attach the artwork to the backing board under the mat. Your artwork should now be neatly matted–an important part of keeping the glass off of the painting.
Turn the frame face down on a clean surface. Open the frame from the back and remove the backing board. Clean the glass or plastic in your frame thoroughly. Allow all moisture to completely evaporate before placing the artwork in the frame.
Place the matted artwork gently into the frame. Make sure that it lies flat. If your frame is extremely deep, pad the empty space with foam core to keep the art from moving. Hold the foam core in place using framing points. Gently lift the frame to check the position of the art.
Place the backing board back into the frame. Secure as it was originally. Your piece is ready to hang.