a) Effects: heat accelerates the deterioration of documents, high relative humidity causes oxidation and, when combined with high temperature, leads to the appearance of mould and insects. Low relative humidity makes paper fragile;
b) Ideal values: temperature should lie between 18 and 20º C and relative humidity between 45% and 55%;
c) Control Mechanisms: adequate control equipment: air-conditioning, humidifiers, dehumidifiers, air purifiers; constant monitoring: thermographs and computerised system; building maintenance.
a) Effects: light accelerates the deterioration of paper, and weakens and yellows or darkens paper. UV rays are particularly harmful owing to photochemical deterioration (high level of energy absorbed by the molecules of the object). Damage is cumulative and irreversible;
b) Ideal values: the maximum light level should not exceed 50 lux/hour;
c) Control Mechanisms: use of UV filters or optic fibre and of low UV ray emission tungsten lamps is recommended.
Effects: acidification and discolouration of paper and leather by action of gases and particles such as nitrogen dioxide, sulphuric anhydride, peroxides and ozone. Particles, of silica in particular, are abrasive.
Cleaning is an elementary, priority and time-consuming task since, to be effective, it has to be systematic and permanent.
WHAT’S IT FOR?
Proper cleaning prolongs the life of a document, avoiding contact with dust, which, in addition to being abrasive, causes the appearance of mold and attracts insects.
HOW IS IT DONE?
Observance of cleaning rules is intended to safeguard the integrity of fragile paper or bindings. In cleaning, the following should be taken into account:
– the physical condition of the documents;
– the type of dirt; the extent of the job;
– and the value of the works.
The area of the archives should be vacuumed regularly and water should not be used. When being cleaned the documents should be closed and cleaning should begin with the dirtiest part, removing items such as clips, elastic bands, bookmarks, photos, pieces of paper, etc.
Necessary equipment: cleaning must be carried out using dusters, soft brushes, bio-alcohol based detergents (with no ammonia or chlorine); the use of gloves and masks, regulated-suction vacuum cleaners and cleaning tables with suction is recommended.