Preventive conservation practices for stone objects should involve minimal intervention. Attempt to do something to improve the stone object’s environment and limit the use of treatment materials that may be damaging to either the stone or the environment. In addition to controlling the temperature and relative humidity levels associated with stone structures, other preventive measures could focus on keeping water away from the stone, pollution and ground water control, visitor management, construction of shelters and wind breaks and even reburial (Doehne and Price 2010).
Avoid sudden or large changes in temperature and relative humidity for stone on display or in storage. Although preferred environmental conditions will vary depending on the particular type of stone, if possible maintain temperatures of less than 20 °C and relative humidity levels in the range 45 – 55 % with maximum variations of 4 °C and 5 % respectively within any 24 hour period.
Do not expose marble or limestone to direct heating from strong lights, sunlight, radiators and the like.
Potential problems associated with handling of stone objects include:
- scratching the surface of highly polished or soft stones (talc, soapstone, marble);
- the absorption of dirt, oil and salts from hands by porous materials (marble, alabaster, limestone); and
- breakage when carelessly handling or moving objects.
To minimise the risk of damage, wear cotton gloves when handling stone. Wear clean disposable latex gloves to reduce the risk of dropping smooth, highly polished stone objects.
When moving stone objects, adopt the following practices:
- check the attachment between an object and its pedestal or base before moving;
- move large objects one at a time. Rest them on thick, soft padding such as high density polyethylene foam;
- use padding such as soft tissue paper, dacron or polyethylene bubble wrap both on the tray and between small objects being moved; and
- pack around protruding parts and distribute the weight evenly.
When storing stone objects consider the following guidelines:
- store small, lightweight objects in acid-free cardboard boxes that have a rigid base;
- place padding under and around objects. Clean cottonwool, acid-free tissue or polyethylene bubble wrap are suitable for padding. Do not compromise the stability of the object by this padding;
- to minimise dust problems, place large heavier objects in closed cupboards or on open shelves with curtains;
- store on painted metal trays or shelves rather than in or on wooden furniture;
- place the largest objects on the lowest shelves; and
- line the shelves with layers of acid-free blotting paper or cotton towels.
Seal wood or wood-based composite materials if they are used for storage (see the chapter Preventive Conservation: Agents of Decay).
Control salt contamination, biological attack and weathering of outdoor stone monuments by isolating the stone from water and salt sources. Achieve this by adopting the following strategies:
- construct a shelter for protection from rainwater. Direct the run-off away from the base;
- construct wind breaks to reduce drying impacts and the impact of airborne salt; and
- isolate the stone monument from the ground or any cement (which also contains soluble salts). Place an impermeable layer such as lead sheet under the stone.
Chemical methods for creating an impermeable layer have also been investigated. Seek the advice of a conservator so that the most appropriate isolation method is used.
Avoid applying protective coatings such as oils, waxes or acrylic resins as these will degrade over time. Although many water-repellent coatings have been developed, review their use carefully before application as these materials have the potential to trap water behind the treated surface layer. In the longer term this may cause surface spalling.