MaterialsMat Board. Preferably archival, at least 4-ply thickness and maybe even 8-ply if you really want it to look like something special. Two sheets: one for the window and one for the backing board, each the size of the finished frame. When deciding what size a mat should be, it's common to choose one size up from the print size. Meaning a 5x7 may be matted in an 8x10 frame, an 8x10 print in an 11x14 frame and so on. My preference, though, has always been for a larger mat—two sizes larger than the print size, such as a 16x20 for an 8x10 print. This is a matter of personal preference, though. Whatever size you decide to make your window mat, allow no less than two inches on any side for it to look its best.
Mat Cutter with Blades. Though there are several brands and styles available, I've always preferred the Dexter mat cutter. All told, it's about a $30 investment that is crucial for cutting the angle that makes a window mat work. Without a reliable cutter, you'll find more frustration than success.
T-square with a ruler edge. Skipping this is the easiest way to mess up a window mat. If you want to cut perfect right angles—and trust me, you do—a straight edge isn't enough. A T-square ensures your cuts remain straight and true. The T-square should also have a ruler edge for accurate measurements.
Photo corners, preferably archival. When artists and gallerists use the term "archival," what they mean is that the composition of the material won't degrade the artwork over time. This usually manifests as "acid free" papers and boards and not permanently affixing the artwork to the mounting. Photo corners allow the print to float free of the mat, and archival corners don't damage the photograph where they come into contact.
Linen or Tyvek tape, also archival. My preferred method of affixing the window mat to the backing board is with a paper hinge, made of archival tape. This holds the window mat in place without compromising the archival integrity of the photo inside.
Pencil. You'll need to make some measurements and marks—on the back of the mat board—and a plain old pencil is perfect. Cotton Gloves. When it comes time to affix the print to the mat boards, cotton gloves allow you to firmly touch the surface of the print without leaving fingerprints.
Work surface. A fairly clutter-free table (because you'll be taking up a pretty big space what with the mat boards and the T-square) is important, as is a consistent cutting surface. You can purchase self-healing plastic sheets or improvise with a large sheet of cardboard or mat board. The important thing is that when you cut through the mat you don't want the blade to dig in and ruin the blade or the table.
The ProcessTo start, lay out the mat board that will become your window with the front side facing down. All of your measurements and marks will be done on the back, the eventual inside of the window mat.
Make your measurements. Let's assume you're matting a full-frame 8x10 print in a 16x20 mat board. You've first got to calculate the amount the mat will overlay the edges of the print. A quarter inch around every side is plenty, and you can likely get away with an eighth-inch overlay, though that makes the last step—positioning the print inside the window—a bit trickier. We'll carry out this exercise with a quarter-inch overlap on each side of the print. So, first, in the center of the back of the mat board, write the dimensions of the board: 16x20. In a column beneath the number 16, which is the short side of the mat, write the dimension of the short side of the print—which you might think would be 8, but remember that for the purposes of our window the print is actually only 7.5 inches wide (because of the quarter-inch overlap on each side), making the actual window size overall a half inch smaller, so instead write 7.5. Then subtract 7.5 from 16 and write the result: 8.5. This is the total amount of mat remaining in the short dimension. But, because it's split between two sides of the print, divide this number in half to arrive at 4.25. Write this down and circle it, because it's the important number. It's the distance from the edge of the mat on the two long sides where the window cuts will be made. Repeat the process for the long dimension: 20 less 9.5 is 10.5, divided in half is 5.25. (For the long dimension, you may want to "weight" the bottom of the mat—offsetting the window slightly upward within the board. If you add a half-inch to the bottom and subtract a half-inch from the top, you'll arrive at 5.75 and 4.75 inches for the window cuts. You may want to skip this step for your first mat, just to keep things simple.)
Now it's time to mark the back of the mat board according to the measurements. With the edge of the mat overhanging the edge of the work surface slightly (in order to ensure the T-square is actually resting on the edge of the mat and not the table) measure 4.25 inches from each long side of the mat and make a hash mark. Then repeat the process for the long dimension of the board, drawing hash marks at 5.25 inches from the edges of the short sides of the mat. Using the T-square to make perfect perpendicular lines, draw lines at each of those hash marks to form a rectangle. You've now got a window drawn on the back of the mat board. The hard part is over. Now it's time for the even harder part.
Set the depth of the blade. Holding the edge of the mat board against the bottom of the cutter in order to determine the proper depth of the blade, adjust the blade so it will protrude far enough to cut fully through the mat, but not so far as to grab in the work surface below. It's a delicate balancing act that may take some practice to get a feel for. You'll likely leave the blade too short on your first try, which leaves you with a partially cut window and a big pain in the behind. Position your mat cutter to cut the window. When I learned to cut window mats like this nearly 20 years ago, a single phrase was repeated over and over: keep the mouse in the house. The mouse is the mat cutter, and the house is the box you've drawn on the back of the mat. If the mat cutter is positioned inside the box, your beveled edges will angle correctly toward the print. Position the cutter outside the box and your bevel will be backwards. If you're like me, you'll still screw this up more frequently than you'd like even though nothing could be simpler. Just keep the mouse in the house. Plunge the blade of the cutter into the mat at the corner of your mark, or just a hair beyond it. Again, this takes time to develop a feel for the perfect spot, but you'll get the hang of it. With the blade in place, slide the straight edge of the T-square until it makes solid contact with the cutter, firming it up to ready it to deliver a perfectly perpendicular cut. When everything is set, and with strong downward pressure on the T-square to hold it in place, begin sliding the cutter until it reaches the corner of the drawn window—or just barely past. Remove the cutter, lift and turn the mat board, and repeat the process until all four sides of the window have been cut. You can use the drawn lines as a reference; if your cut drifts far from the line you probably made a bad cut, and it was probably due to a sliding T-square. Again, practice makes perfect.
Finish the edges. In most cases, there's at least one corner that wasn't cut cleanly. Use a blade, removed from the cutter, to make tiny finishing cuts and clean up the corners. This is easiest with a new, sharp blade. If all has gone according to plan, you should now possess a cleanly cut window mat. Lay it face down next to the backing board and butt them together tightly. Then, cut three strips of linen tape and adhere them to the boards in order to form a hinge along the edge of the board. Some folks prefer to hinge the top, while others prefer the side. Do what makes you happy.
With the hinged mat complete, it's time to position the print inside the window mat. Swing the window open and put the print in place. Using a gloved hand, reach through the window and hold the print as you close the mat and adjust the position of the print. Once it's perfectly in place, still holding it firmly with a gloved hand, reopen the mat. Some folks mark the edges of the print in order to determine where to place the archival corners, though my preference is simply to apply them one by one as I hold the mat in place for at least the first corner. Occasionally, this approach requires a bit of fine-tuning after I stray a bit, but this is an adjustment that doesn't require throwing out the whole mat and starting over.
With the print in place and held at all four corners, swing the mat closed and admire your work. It's now ready to be framed, which is a whole other time-consuming process in and of itself. At least now you know your work is professionally presented and archivally protected—and that's about all you can ask from a few sheets of paperboard.