Cut a piece of acid-free mat board to match the internal dimensions of the frame, using a mat cutter or a straight edge and craft knife. Without an over-mat, the under-mat will become the visible border around the artwork, so choose a neutral mat board color or a color that complements the artwork.
Center the artwork on the piece of mat board, using a ruler to ensure equal border widths on all sides. Stabilize the artwork by placing a small weight in the center. Place a piece of scrap paper between the weight and the artwork to prevent the weight from marring the surface of the art. Lightly outline the corners of the artwork in pencil.
Cut four 4-inch long strips of framing tape to create two mounting hinges. Find both self-stick and water activated linen tape from art and framing suppliers, or make homemade tape with strips of rice paper and rice starch paste. Rice paper tape is the most appropriate choice for delicate works of art.
Fold down the top edge of the artwork.
Fold two strips of tape in half with the adhesive-side facing out. Create sharp creases by running a bone folder along the fold. Affix the folded strips in and down at least 1-inch from the pencil-marked corners.
Place the other two pieces of tape horizontally, tucked inside the folded pieces like hands under armpits, and stick them to the mat board. Do not let the outer ends of the tape extend beyond the pencil marks, as they will end up showing from behind the artwork.
Drop the artwork down, allowing it to stick to the folded down flaps of the mounting tape. If the bottom of the paper curls up, hinges may also be needed at the bottom corners. Place pieces of scrap paper over the corners and set weights on top, to press the hinges for a few minutes while the adhesive cures.
Position the artwork at the back of the frame and secure the frame backing behind the mat board. To float artwork, employ a deep frame with spacers. Spacers sit between the glazing and mat board and keep the artwork from touching the glass. Without spacing, condensation may form on the inside and damage the artwork.