Rubber cement is an inexpensive glue made from rubber that has been liquefied with chemical solvents. The glue "dries" as the solvents evaporate and the rubber forms a thin solid layer. It is intended primarily for gluing various types of paper products together. However, as useful as it is, rubber cement is not the best fixative to use in all situations. Knowing both its advantages and limitations is important if you want to get the best use from this convenient adhesive.
Ease of Application
One of the beauties of rubber cement is how easy it is to join two surfaces using it. It can be applied to only one surface and the two surfaces joined while the cement is still wet -- a process called "wet mounting." You can adjust the joint while the glue is wet, then hold the two pieces together until the glue sets, providing a quick joint that is not particularly strong. However, it can also be applied to both surfaces and allowed to dry before they are joined, a process called "dry mounting." This results in a very strong bond, although the surfaces cannot be adjusted once they touch.
Ease of Cleanup
Another benefit of rubber cement is ease of cleanup. If too much glue is applied and runs outside the area where you meant to apply it, simply let it dry. Since dried rubber cement will not stick to anything but itself, simply rubbing your finger across the dried excess will cause it to release its grip and ball up under your finger. Just throw the dried glue away. Some manufacturers also provide special tools for performing this "balling" procedure if you do not want to use your finger.
Over time, rubber cement loses its "stickiness." Items bonded with rubber cement will gradually just "let go" of each other. The adhesive does not simply evaporate; rather, it dries out and leaves a brittle residue where it was originally spread. This residue is not easy to remove and can damage the item it was intended to bond, especially if that item was something fragile like a photograph. This is one reason that rubber cement is not recommended for use with original artwork.
Not only does rubber cement lose its ability to stick things together as it ages, it also suffers a chemical breakdown. Rubber cement is rubber made into a liquid by the addition of various organic solvents, and these solvents are very volatile; they cause chemical reactions as they break down. One of those chemicals is sulfuric acid, which can leave yellow stains and otherwise damage the materials they touch. Never use rubber cement on important artwork or photographs that you want to keep; it should only be used on expendable projects.