Keeping in mind the above definitions, whatever the article is, a restorer would then only perform the procedures to preserve, while not causing any further damage to the piece. Examples of these are the items you see in museums. If there is an old pottery or porcelain on display and it has been cracked, most likely the restoration will be quite visible. Dissolvable adhesives and soft clay fillers are used to only maintain the shape or appearance of the article. If the item is wood then in most cases the finish is left alone and only the structure is preserved by using the same adhesives that were originally used as well as using a piece of wood the same age to restore missing parts.
Some oriental restorers use gold to fill in the cracks or chips on a damaged item.
They respect an item for its existing condition and prefer not to conceal the damage. Master oil paintings are treated with exceptional care, nothing should be used that is not reversible. Any painting or paperwork with great value needs to be brought to the conservator for the correct procedures for restoration. An amateur can cause damage that may be permanent and impossible for even the best conservator to reverse. Removing an old patina on a metal item such as bronze, may bring the value down.