A Brief Tour of Window Mats and Their Openings. In this blog we will try to shed some light on Window Mats and Their Openings, with a particular focus to their external and internal sizing. A window mat ( Customers often call them edges, cardboards, surrounds, masks, etc ) or a window mount, as our English brethren would call one is that white or coloured cardboard that framers often put around images and inside picture frames. Broadly speaking, window mats are placed over and around images for several important reasons. The two main ones would be: a) the thickness of the mat ( around 1.2 or more millimetres) helps to keep the glass away from touching or rubbing the art and, b) the sides of the window mat distance the image, or art, from the frame, this facilitates a better perception and appreciation of the art away from the visual distraction of the adjacent wood frame ... . For a quick reference explaining the basics of a picture frame and its compenent please visit our page detailing the picture frames parts names . You probably won’t see a mat around a poster but you’ll often see one around a photo frame or picture frames that commemorates an important event, like a wedding, for instance. Window mats, or mats from now on, are a disparate component, almost invariably hand-made, precision cut and assembled by professional picture framers. It is not to be confused with the white margins or borders photographic laboratories often include and print with images. Most window mats are cut from matboard sheets which are commercially produced for a price. A minority of matboard sold is of higher quality, such as archival, conservation or museum quality. The advantage, disadvantages, pros and cons of each will not be discussed here as it would be beyond the scope of this post. Regardless of its quality however, when cutting mats from sheets, both external and internal sizes are important and need to be precise, and within a few millimetres, to be exact. Let us begin with the external, or the outside size of a mat. Picture framers generally measure the inside of an assembled frame and would cut the outside of the about 4 or 5 millimetres shorter. Thus if the inside of a frame measures 600x400mm, the externals size, or the outside of the mat, would be cut at 596x396mm.
The reason for the mat being cut slightly smaller than the inside of the frame is for clearance. Unless there’s a small clearance the mat would need to be forced or jammed inside the frame. Not only this is bad picture framing as it could buckle and ruin the mat, but such an interference fit would also prevent material expansion, and most likely leading to the mat bending or cockling, both unsightly and undesirable. We now progress to cutting the inside of the mat. Some framers call this the “exact mat opening” others the “opening” or the ‘cutout” but we, along with most framers, will call it simply the “hole”, because, well, it is a hole cut into the matboard! The matboard hole goes over the photo or image as typified below: