A painting consists of three or more layers:

• The support (canvas, paper, cardboard, wood, metal, stone, glass or other)
• The preparation: a white, red, grey, black, Brown or other color layer that consists of an adhesive, water and chalk
• The paint layer: a medium, a solvent and pigments
• The varnish layer: usually of a mixture of a resin and a solvent.
• Possibly another or various other layers

When one of these layers deteriorates or breaks or separates from the one underneath, due to mechanical, chemical or temporary decay, an intervention is necessary either as a conservator or a restorer.

When this happens, the conservator/restorer intervenes through a process of conservation or restoration.

Conservation is an indirect intervention on the painting that will not actually touch or affect the layers in themselves. It will not change the composition or chemical structure of the object.
Restoration is the direct intervention on the object, either by physical, chemical or mechanical action.