The Backing Board
Mounting Animation Cels
written by Kenneth Allred - May 28, 1998
Step 1. The Backing Board
The backing board I use is 1/8" thick acid free foam core. You can buy a 32x40" sheet at your local Art Supply store for about $7.00. They will even cut it for you for free into smaller pieces to fit an 11x14" frame.
Step 2. 
The Background
Unless you like white, or your cel has a drawing stuck to it that you don't want to remove, then you'll probably want to add a background color to enhance your cel's appearance. Your Art Supply store will have sheets of acid free paper available in a variety of colors.
If your cel came with a matching production background, then chances are it is wider than 14". Please do not cut it to match the frame, as this will destroy it's value! Rather, you will need to use a wider frame, and adjust the dimensions of everything to match.
Step 3. 
The Lower Inner Matte
The inside mattes are made from 1/16" acid free mat board. These are available in 32x40" sheets from your local Art Supply store at about $5.00 a sheet. Have them cut each sheet into 11x14" pieces for you. The opening, you can cut out yourself using a razor knife and a straight edge. Leave 1" at the top, 2" on each side, and 1 1/2" at the bottom. This will allow the matte to overlap the cel approximately 1/8" on each side.
Step 4. 
The Cel
Before touching your cel, you will at least want to thoroughly wash your hands. You may also want to use cotton gloves, which are available at Art Supply stores. In any case, handle the cel as little as possible, and only from the edges. And be very careful not to bend the cel, as this could cause the paint to crack.
The cel is centered in the matte opening so it overlaps evenly on all sides. Secure it with small pieces of acid free tape applied only to the top corners of the cel. This is to allow for expansion of the cel and/or matte over time.
Step 5. 
The Upper Inner Matte
This matte is the same as the matte used in step 3. The mattes are dimensioned to hold the cel with the minimal amount of physical contact. If you have a multi-cel setup, then I would recommend repeating steps 4-5 for each layer (if they're not stuck to each other). This will give a nice 3D effect, and prevent the cel layers from sticking.
Step 6. 
The Outside Matte
The matte I use for the outside is a standard pre cut acid free matte available at your local Art Supply store. For an 11x14" frame, the matte's opening is 7 1/2" x 9 1/2". This more than covers up the inside mattes, and will give your cel the appearance of floating inside the frame.
Step 7. 
The Glass
Unless you plan on hanging your artwork in a dimly lit hallway, then I would recommend using UV resistant (conservation) glass. Otherwise, you may find that your cel has yellowed after a few years. I have a preference for non-glare glass, but it does seem to cut down the contrast of the cel a bit. An 11x14" sheet of non-glare conservation glass will cost you about $20 at an Art Supply store. The regular conservation glass is only $10. Which one to get depends on your lighting conditions, your budget, and personal taste.
A word of caution about handling conservation glass... It gets it's protective qualities from a thin UV resistant coating on one side. Do not use glass cleaner on this side of the glass, as it may damage the film. The coated side can be identified by printing along the edge. This is the side that should be facing the inside of the frame.
An alternative is to use UV resistant plexi-glass. This is less expensive than glass, but because plexi-glass tends to attract dust, and is not very resistant to scratching, I prefer to use glass.
Step 8. 
The Frame
An inexpensive 11x14" wooden frame can be found at your local Crafting or Art Supply store for about $15-$20. If you purchase one of these, you will want to replace the glass (not UV resistant) and replace the backing (not acid free). You will also want to make sure the frame is thick enough to hold your cel and mattes.