CONSERVATION (T4) Flashcards
What are the key considerations for the environmental protection of artefacts rather than occupants?
- The building itself
- The contents of the building
- Both building fabric and contents
key environmental parameter that need to be controlled
temperature moisture / humidity light exposure pollutants pests/ mold
nature of the environmental protection depends on the material types and how it is displayed
organic inorganic in situ in context in an environmental enclosure
organic material
Plants and animals contain a high proportion of water, so it’s unsurprising that their products also retain moisture.
When materials absorb and retain moisture, they are described as hygroscopic.
Such materials can and will absorb or give off moisture until they reach a state of equilibrium with the air that surrounds them.
organic artefacts
- Wood • Paper • Cotton • Linen • Wool • Silk
- Parchment • Leather • Fur • Feathers • Ivory
- Bone • Horn
what can hygroscopic materials do?
swell and shrink repeatedly
causes internal stress and damage.
(This is particularly a problem in composite objects where the different materials have different rates of shrinkage/expansion.
The shrinkage (or expansion) of one material may force changes in the dimensions of another, causing considerable tension and eventually damage, e.g. paintings on wooden panels.)
Temperature
Fluctuating heat, however, can damage or compromise items in indirect ways. Uncontrolled temperatures can:
• Cause changes in humidity.
• Speed up chemical processes and biological activity.
• Affect the comfort of people working with or visiting collection items.
The humidity of the air depends on the temperature
Where one cubic metre of air holds 10g of water at 10°C, the same volume can hold over 30g when the air is heated up to 30°C.
(absolute humidity )
Relative humidity
Relative humidity (RH) is expressed as a percentage of the maximum amount of water the air can hold at that temperature.
recommended relative humidity
Relative humidity should not drop below 40% or rise above 70%.
40% = cause sensitive items to become dry and brittle 70% = fungal growth begins
stability
When the temperature changes, for instance after the sun has set, so too does the RH. This principle is one of the most important factors in environmental control in a museum.
Sudden weather changes can cause dramatic fluctuations if the building is not insulated.
Direct sunshine through windows or skylights can cause considerable heat gain and day-night variations.
factors to consider about stability
‣ Poor air circulation or ventilation can create micro- climates that differ from ambient conditions.
‣ Visitors produce moisture, especially on rainy days.
‣ In-case and spot lighting can create localised pockets of
high temperature and low RH.
‣ Radiators or heating units placed beneath items can cause severe drops in RH for that item.
‣ Display cases can be designed to create favourable micro-climates for an item.
Light exposure
Good lighting is essential for museums/heritage buildings because people visit primarily to view the collections/exhibits/spaces.
Lighting can create the atmosphere and it can draw attention to some of the most intriguing items on display.
Light also means damage. Dyes and pigments fade when exposed to light, even at low levels, and the effects are cumulative.
cumulative light exposure
Cumulative light exposure (or light dose) is measured in
units of lux hours (i.e. illumination x time).
recommended annual exposure
Annual exposure is the light dose that an object receives over a period of 1 year.
• For very sensitive items, 100,000 lux hours.
• For moderately sensitive items, in the range 450,000 to 600,000 lux hours.
