If you have glue residue on the surface of something, whether from a previous application or from an accident, removing it is not impossible. There are, in fact, several different ways of removing glue, but the method is dependent on the surface in question. Following are some suggestions for removing glue from various surfaces.
For getting rid of glue left behind by stickers, price tags, and other manufacturer or store applications, try simple rubbing alcohol. Moisten a cotton ball or soft cloth with rubbing alcohol and hold it over the area in question. Once the residue is thoroughly moistened, gently scrape the glue residue off and repeat the process until the glue is completely removed. Glass, plastic, and ceramic surfaces should not be damaged by rubbing alcohol, but test a small area if the surface is painted or made of fabric.
Removing glue from pictures, baseball cards, or other paper products may be more difficult. The general idea is to dissolve the adhesive bond without compromising the fibers of the object. Paper can generally be frozen without damage, so try placing the object in question into your freezer. You may be able to stiffen the glue to a point brittle enough that it can be scraped off with an Exacto knife or razor blade. Steam may also be effective at removing glue from paper.
To remove dried glue from fabric or carpet, try holding an ice cube in a plastic baggie over the spot. Your objective, similar to the above technique, is to make the glue brittle enough to be scraped away. The plastic bag will ensure that additional moisture does not re-activate the adhesive properties of the glue.
Taking glue from wooden surfaces can sometimes be accomplished with warm vinegar. Moisten a cloth with warm vinegar, and after some compression, try rubbing away the glue. Be cautious when scraping glue from wood if you are concerned with damaging the surface finish.
The best way of getting the glue from wallpaper backing is to steam it. You can rent a portable steamer, and if you are working in a well-ventilated area, try combining the use of steam and commercial wallpaper adhesive removers. For older homes with older wall coverings, this will be a repetitive and labor-intensive process, but with persistence, it should work. You will also need a flat putty knife with a wide head to scrape the glue as you steam it.
The scientific process behind removing glue is simply the destruction of the adhesive bond through altering its moisture and temperature levels, without destroying the object to which the glue is bound. Commercial adhesive removers should be used with caution on surfaces that can be damaged unless you plan to cover the surface with something else.