Why is matting important? 

Matting, the colored border around your art, is used not just for colour but also to keep the glass from coming into contact with the art and to provide a space for air to circulate. Differences in temperatures can cause condensation to form inside the glass, which could lead to mold or mildew as well as damage to inks and colours. 

Placing the art directly against the glass can also result in wrinkles or "buckles" from expansion and contraction due to changes in temperature. 

If moisture does happen to get inside the frame, it can also cause your art to stick to the glass. When you try to remove the glass, it usually results in tearing the art. 

Using the right kind of mat is also important. beware of using a non-acid-free mat if you want to preserve your art for a long time. Non-acid-free mats are made from ground wood pulp which contains high levels of acid that can transfer to papers that come into contact with it. Art framed with this type of mat will eventually absorb some of the acid, resulting in a yellowish-brown burn line along the inside edges of the mat. Backing your art with cardboard has the same negative effect. 

When conservation framing is required, an acid-free mat made from cotton fibres or chemically purified wood pulp along with an acid-free foam core for the backing are preferred.