The action of time
Objects age naturally due to contact with the outside environment, even when the latter is not directly harmful: even weak light turns wood and paper yellow, for example. Some materials - including certain unstable pigments or glazes - also contain self-destructive elements. The effects of time give an object its "patina" - its historic dimension, the guarantee of its authenticity - and should therefore be respected !
The action of the environment
An object’s immediate environment is often the principal cause of its deterioration. The term "environment" includes:
. climate (temperature, humidity, hygrometry): humidity causes metal objects to rust, for example, which is why relative humidity (RH) should be below 40%, whereas most other objects require 50-55%. However it should be noted that strong climatic variations cause the worst damage, causing wooden items to crack, for example. Climate is fundamental: harmful elements such as moulds and pests can thrive in an unsuitable climate.
. light: it yellows paper and wood, dulls pigments and colourings, and is one of the graphic collections’ worst enemies! This is why exhibition lighting is strictly controlled (50 lux per hour, one month a year for textile and graphic collections)
. pollution: it contains dust, gases, and acids from which the works need protection.
. infestation: predators and parasites.
Pests and moulds are the major threat to organic materials (textiles, wood, leather, paper, etc). Insects can cause profound alterations to an object, creating networks of galleries (parts eaten by larvae) and holes (through which the adult insects emerge). These insatiable gluttons can reduce a Norman wardrobe to a pile of dust.
Natural disasters (fires, floods...) can cause sudden and dramatic upheavals in the objects’ environment, and provoke considerable damage.
We can differentiate between deliberate damage (vandalism) and unintentional harm (unfortunately the most common): incorrect handling, clumsiness, former restoration work which ultimately spoils rather than preserves an object... On the other hand, the way objects were used before they entered the museum (in the case of tools, for example) creates the kind of wear which gives an object its significance and therefore its value, contributing to its precious "patina".