Contaminants

This candlestick shows damage from foam used to protect it. The images show the degraded foam on the metal, the blue corrosion caused by the foam, the site after cleaning and a full view after treatment.

Contaminants are the materials that pollute our objects. Some are in our environment, some are accidentally brought in, and others are deliberately introduced. Here are some of the more common examples:

• human skin is moist, oily, acidic and sometimes dirty - just handling objects can damage them. Wearing protective gloves when handling objects will protect the object, but the gloves themselves can actually cause damage if the wrong type is used. Gloves with dimples (for better grip) can leave permanent spotty marks on polished metals and glass (the dimple material causing corrosion) and knitted handling gloves can catch on loose paint flakes or splinters. Some other synthetic gloves, long considered safe, are now thought to pose a risk to some materials.
   
• dust - abrasive as well as disfiguring
   
• acid rain - will dissolve the stone that forms many of our public buildings and pieces of art
   
• off-gassing - the gases released by storage units and display cases made from oak, MDF, plywood, resins, paints, adhesives etc. The acetic acid from oak is notorious for causing lead to corrode and seashells to become disfigured
   
• some fumigants - gases used to rid objects of pests - can discolour dyes and pigments, corrode metals and damage photographs
   
• the acids in newspaper and acidic cardboard
   
• corrosive substances like harsh cleaning fluids, bleaches and caustic soda
   
• new paint - objects placed in newly painted, though 'touch dry', display cases can stick and suffer surface damage
   
• inappropriate 'conservation' treatments - some adhesives and varnishes discolour or become irreversible; chemicals might affect DNA in plant and animal specimens; insecticides may leave disfiguring or harmful substances in or on objects

As with most of the other agents of destruction there are ways to prevent contamination:

• wear clean, protective gloves when handling objects (but choose the right type)
   
• keep areas around objects clean and clear of clutter. If using chemicals use appropriate containers which are properly labelled and avoid spillages. Always refer to health and safety information
   
• use inert materials in display cases and storage containers (avoid wood products, especially oak, MDF, plywood). At National Museums Liverpool we test all our display case materials and take steps to prevent the effects of off-gassing
   
• use pollutant scavengers such as activated charcoal to 'mop up' harmful substances (eg acetic acid)
   
• only repair objects using materials approved for conservation use and suitable for the job in hand
   
• avoid locations with high pollution or dust and with high local emissions (e.g. roadways)
   
• supply filtered air to galleries and cabinets

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