Restriction of movement is the primary reason that art buckles in a frame. Several things can cause this, but one of the most important is that paper expands and contracts with changes in temperature and humidity.

If you have noticed a ruffle around the edges of a photo or paper item that has been put into a frame with mounting, it is caused by expansion of the paper. Art on paper that is placed directly in contact with the glazing reacts to humidity around the edges next to the frame, causing expansion of the outside edges. The more pressure that is applied to the backing, the more buckling will result. Glass transfers heat better than air, so paper in contact with the glass will expand and absorb any condensation that collects at the point of contact.

1. Suspended by hinges.
2. Edge supports, such as mounting strips, pocket corners, or sink mats.
3. Full mounting, meaning it is wet pasted, dry mounted, or mounted with a full sheet of pressure-sensitive adhesive. Spray mounting is only effective on smaller items.

1. The matboards, filler boards, or mounting boards are cut too close to the rabbet of the frame; always provide at least 1/8" allowance.
2. Hinges are too restrictive, holding the top edge too tight and not permitting expansion of the art.
3. Tape runs across the entire top of the art. Again, this is too restrictive and causes ruffles.
4. Double stick tape is used as an X in the center of the paper, around the edges, or at the four corners. This holds the artwork too tight. The unmounted paper will expand, causing buckles. In a short time, the impression of the tape will also be visible.
5. Art suspended from the window mat will buckle and separate from the mat because it is pulling down on a weakened board. Art should be attached to the backing board.
6. Uneven layers of boards and art. If the art is thick, a lift mat should be attached around the edge to allow the art to move under the mats.
7. The art may be printed off-grain. The grain on the paper should run horizontal so when moisture sets in the art expands downward. If it has been printed with the grain of the paper running vertically, the art will expand between the hinges. A possible solution is to make the hinges very loose, using a pendulum-style hinge attached to the backing board.
8. The use of spring clips on metal frames will cause the sides of the mats and art to be forced towards the center of the framing. This pressure will eventually force the boards inward, causing mats to separate at the window and the mats and art to buckle. A poster dry mounted to foamboard should be okay, but any art framed with layers of mats and art will buckle from the pressure. Use a full sheet of board to fill up the space; it will look better, too.
9. Excessive pressure from points or nails will cause mats and art to buckle because they use up the necessary allowance for expansion. Hold a point driver flat on the stack of board when you insert the point.
10. Force fitting a stack of mats into a rabbet that is too small can cause buckling. If the stack doesn't fit, add a small moulding or RabbetSpace to minimize the pressure.
        If an item to be framed is already buckled, such as a watercolor or skin document, do not force it to be flat. That will only cause more buckling and damage the item. Instead, allow space for the item and create multiple levels with mats and a spacer to add dimension. It will improve the look, allow the piece to live longer, and show its real character.