The care of organic gem materials: some of the causes of damage and how to prevent them.

TEMPERATURE
High temperatures cause deterioration to occur faster, and often helps to dry objects out. Putting organic objects near heaters or under hot lamps should be avoided, and in the long-term cool temperatures will help objects to last longer.

Warped tortoiseshell brush back, some pique work missing,, possibly damaged by heat.

HUMIDITY
The amount of moisture in the air relates to the amount of moisture in organic material. This moisture bulks out the object and helps give it shape and form. Alternating high and low humidities cause the object to absorb or give out moisture and thus alter its shape and size, often in a damaging way.

In low humidities, when objects are dried out by hot spotlights or the drying effect of winter central heating, desiccation occurs. The effect of this moisture loss from organic objects causes them to shrink, split and crack. The effect is exacerbated by the shrinkage being different in different directions. Thus, wood will shrink along the width of planks but not along its length. Ivory will do the same, splitting longitudinally and sometimes forming a cone-in-cone structure on cross-sections. Materials such as ivory, with both an organic and inorganic content, are very sensitive to moisture levels and should not be soaked in water. When cleaning, very little water should be used and the object should be dried immediately. Materials with very little organic content, such as shells and pearls, are little affected by humidity changes and can be gently washed in water with a neutral detergent (such as used for washing delicate woolen material) rinsed in clean water and dried with a soft cloth.

Ivory statuette showing longitudinal cracking from surrounding humidity changes.

At the other end of the scale, warm, damp conditions will encourage mould to grow on organic materials, damaging surface decoration and weakening the structure. It should be noted that moulds can affect some people with asthma symptoms and so should be cleaned off in a well ventilated area.

High humidities can also encourage some insect pest damage. Furniture beetle (woodworm) attack is commonly known, but some softer organic materials, such as horn, are vulnerable to attack from the larvae of clothes moth and carpet beetles. Good housekeeping and general high standards of cleanliness will normally prevent this.

LIGHT
We tend to forget that light is not just what makes things visible so that they can be seen and enjoyed, but also contains the damaging wavelengths of infra-red (heat) and ultra-violet radiation. The infra-red radiation causes the heat and moisture damage mentioned above, and drying out and shrinkage of organic materials. Direct sunlight and hot spotlights are particular criminals. Ultra-violet radiation (UV), present in all light sources, are very chemically active and are the major cause of chemical degradation such as fading and surface deterioration. Organic pigments in paints, dyestuffs and other coloured material such as wood, are vulnerable to rapid fading in daylight and under some high UV artificial lights. Organic gem material copies, such as vulcanite (a jet fake), is easily identified as it fades from black to olive brown under daylight and gives off a sulphurous smell. Other material, such as ivory, is bleached by UV, which is why it used to be recommended to leave the piano lid up to keep the white ivory keys white. ( Ivory that has darkened will bleach eventually in sunlight or better still under a UV lamp which has no heat content, though it does take a bit of time.) Vulnerable coloured material should be kept out of direct sunlight and not placed close to artificial lights. Museums and galleries protect their material by applying a clear UV filter film over windows and on picture glass and display cases.

POLLUTION
This is a loose definition of unwanted chemicals that can cause both aesthetic and structural damage to delicate objects. Atmospheric pollutants are often highly acidic and often contain sticky black particles from the combustion of coal, gas, oil etc. The combination of both can cause chemical and aesthetic damage to objects exposed to them. Inside buildings, other forms of pollution can be damaging.

Building materials, carpets, furnishing, pesticides, floor cleaners etc. can all contribute to chemically active gases that in the long-term can damage the occupants’ health and their belongings. Some materials, such as oak, give off acidic vapour that can attack shell, pearl, metals etc. In museum show cases, the construction materials are tested to ensure they are inert, as axiomatically objects can be displayed in these well-sealed environments for many years – allowing the level of acidic gases to build-up and cause damage often on the unseen side of the object.

And of course, there is the mechanical, chemical and other damage caused by using organic gem material for its proper purpose, which is its use. Pearls are prized as neck and wrist decoration, yet are readily damaged by any acidic products from the skin or from soaps, perfumes, deodorants etc., that they may come into contact with. Amber may be damaged by bad stringing on necklaces that cause the brittle materials to bang against each other.

Organic gem materials are special in that they mostly come from an animal or vegetable origin and have the special characteristics of beauty, age, uniqueness and rarity that gives them value. A basic understanding of where they come from and what will hasten their deterioration will ensure that they will be properly looked after and cared for.

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