There is no one correct way to mat something but there are lots or guidelines to help get you started. My demo shows how to make a fine mat without the need for an expensive mat-cutter. We'll do it all with readily available hand tools.
Before you buy the matting materials, decide what type of board you will need. Mat boards are made in various thicknesses and from various materials. I always recommend getting the best product you can afford. A handmade print on expensive paper should be matted with a high quality mat board while a drawing made on newsprint could probably be matted with poster board or less expensive matting material. Acid free is good; all-cotton acid free boards are best.
We're going to use a 4 ply acid free museum board for this project, but you can use any good quality mat board.
Step 1: Tools You Will Need
Snap-Off Blade Cutting Knife
24 inch or longer Cork-Backed Straight Edge Ruler
Mechanical Pencil or a well sharpened Number 2 Pencil
Pony Clamp or other spring action clamp
Seamless cutting mat or a large sheet of heavy weight Chip Board to protect the surface on which you are making cuts
White or cream color 4 ply Museum Board, Mat Board, or Poster board
Hinging material - 1 inch strips of archival quality sketch paper or lightweight inexpensive Japanese rice paper
Elmer's glue, SOBO brand or other white flexible glue
1/2 to 1 inch bristle brush
Burnishing tools: bone folder, or a plastic disposable knife (optional)
A weight such as a paper covered brick
Step 2: Proportions and Other Aesthetics
For example, you might want to make a mat for a medium sized print with a 3 inch border along the top and sides of the window and 4 inch border along the bottom.
The reason for this is because of an illusion of perception. Sometimes, when you look at something that is centered in a window mat or mounted on a board, your brain will perceive the work to be slightly below center and therefore, it can look look awkward and bottom heavy.
By increasing the border along the bottom, the work will appear to look balanced and right where it should be. This is not a hard and fast rule though and sometimes people will make a mat with all borders at the same width.
Step 3: Measuring
Decide how large your window borders will be. Remember that the left and right sides of the mat are the same width. The top border can be the same width as the sides but the bottom of the mat will be about an inch taller than the other sides of the window.
Add together the measurements.
The width of the image plus the two side borders of the window equals the horizontal measurement of the mat.
The height of the image plus the top and bottom borders of the window equals the vertical measurement of the mat.
Step 4: Cutting the Mat
The first step is to make sure your boards are square. This can be done by using a nice clean carpenter's square or a plastic drafting square and a straight edge.
When transferring measurements make the tiniest marks possible with your mechanical pencil along the edge of the board. Only you need to see where to put the ruler and you'll only need a mark at the top and bottom edge of your cut.
The pony clamp is used to help secure the board and the straight edge to the edge of a work table. This keeps everything in place at the bottom edge of the board and frees your hand to hold the ruler down at the other end.
The most important part of cutting is to make sure your blade is sharp and that you make several passes along the edge of the ruler. That way you make a cleaner, smoother and less dangerous cut. If you try to cut through the board in one pass, the knife could slip and make a less accurate cut or if it were to skip onto the ruler, you could give yourself a nasty cut.
After the boards are cut, lay out your window measurements on the back of one board and cut out the window. A good tip is to remember to place your ruler with the cutting knife side toward the inside of the window mat rather than toward the outside. That way if you swerve a little making your cut you won't damage the window part, just the part that you are removing. And there you go, you've cut the mat.
Remember to make all marks in pencil on the back of your boards.
Step 5: Join Boards
The strip should be about 1 inch wide and the length of the boards you are joining together. If your hinge is shorter than the width of the mat you can use more than one strip to span the hinge.
I use a cheap bristle brush from the hardware store and white glue that I've decanted into a wide mouthed container. That way I can easily dip my brush into the container and spread the glue on the hinge.
Lay the boards together, inside facing up, top edges touching. Mark a line on one side about 1/2 inch from the edge. This is the edge you'll use as a guide when you apply the hinge.
Brush glue on the hinge strip, brushing in one direction. A back and forth brushing motion can sometimes create problems. See picture below.
Place the hinge on the seam, and gently flatten. Rice paper is delicate when wet and easily torn. Fold the window over the backing board and adjust as needed. Trim off any over hang. If you trim while the glue is wet use a very sharp knife. If you're not sure wait until the glue has dried, then trim away any excess.
At this point you can take a little break. 10 to 15 minutes. Let the glue set. Then we'll finish the project.
Step 6: Final Steps. . . Attaching the Artwork
The hinges are about 2 inches long and about 1 inch wide. Fold them in half the long way. Apply the glue to the hinge, then apply the hinge to the back of the work along the top edge and then gently attach the work to the backing board. Close the window and if needed make any minor adjustments in placement before the glue sets.
Please, never use rubber cement or spray adhesive. Besides being bad for you, they contain properties that, over time, will discolor and damage your work.
Paper is an organic material and responds to the moisture (or lack of moisture) in the air by continually expanding and contracting. Improperly mounted works can buckle and otherwise become damaged if they are too securely attached to their backing boards. The best way to approach it is to use only what is necessary to hold the work to the board. Finally, if you ever need to remove your work from the mat you can simply slice the hinge and take out your piece. No need to worry about removing the hinge from the back of the work. If you used good paper for the hinge and a white water based glue, it shouldn't damage the work.