Confusion sometimes arises about the terms “restoration” and “conservation.” Restoration is actually a type of conservation treatment. Specifically it refers to an attempt to bring an object closer to its original appearance. The other type of conservation treatment is stabilization, which refers to an attempt to prevent further deterioration of an object. In all conservation treatments the integrity of the object and maintaining as much of the original material as possible is important.
In glass conservation, a stabilization treatment might include re-assembling the fragments of a broken object, but not making any fills to replace the missing pieces unless they are needed for structural support. A restoration treatment would include making fills to replace the missing fragments so that the object looks whole once again. Conservators do not want to deceive anyone into believing an object is undamaged when it’s not, but the repairs also should not distract from the object itself. As a general rule, restorations should be invisible/unnoticeable from 6 feet away, but visible (to a trained eye) from 6 inches away.