It is recommended that all original works on paper be framed with acid-free materials for preservation purposes, sometimes called 'museum mounting'. This includes acid-free mats on the top of the work of art, and acid-free backing behind the artwork. Less expensive regular mats, used for posters and reproductions, have a high acid content. Over time (10+ years), the acid in the mat leaks out of the cut edge of the mat, and will turn the beveled edge of the mat a yellowish brown, as well as stain the artwork underneath. Staining from acid will reduce the value of the work of art and create an overall aged look to the framed piece. When acid-free mats are used, a work of art can look fresh and new forever. To determine whether a work of art is framed with acid or non-acid mats, look closely at the beveled cut of the mat around the image of the artwork. If the bevel has a pure white core, it is acid-free. If it has a yellowish or cardboard look to it, it is usually a regular mat. To hold original artwork in place, thin strips of acid-free surgical adhesive are applied as hangers onto the back of the artwork. These are then attached to the acid-free mats. An original work of art should always be able to be 'freed' when unframed. Larger works of art on paper require oversized materials, i.e., oversized mats and glass. Regular sized mats are 32 x 40 and oversized mats are 40 x 60. Oversized materials increase the cost of framing. Additional mats, spacers, liners, filets and V-grooves can be used to create different looks in the framing. The styles and costs of the mouldings, or frames, vary greatly. Metal mouldings or inexpensive contemporary wood mouldings are often used for posters and some works on paper to keep framing costs low.     Posters require dry-mounting which is a process by which a thin mist of glue is sprayed onto a piece of thin cardboard upon which the poster is placed. The two pieces are then put into a dry-mount press where heat is applied to assist in adhering the two units. Dry-mounting will prevent any wrinkling or buckling of the image once it is framed. Dry-mounting is never used with original artwork. Dry-mounting an original work of art will destroy its value.