General guidelines for the cleaning, ‘development’ and repair or consolidation of rocks and minerals are provided by King (1992b). Some of the key points made by King and others in the same publication are outlined below.
Only undertake any treatment if the mineral type and its properties are well known. Irreparable damage may occur if inappropriate treatments are applied.
Restrict cleaning of rocks and minerals to the removal of dust, dirt, clay and similar materials.
If it is necessary to immerse rocks during cleaning then ensure the liquid and the rocks are at the same temperature before immersion. This will reduce the risk of thermal shock.
Water will affect some minerals. Rock samples are generally more tolerant of water-based cleaning than are mineral specimens. Ethanol and propan-2-ol have been used to remove clay from water-soluble minerals. Some wet cleaning methods which may be useful for water-resistant samples are described earlier in the Stone section.
Dry cleaning techniques including gentle brushing, vacuuming with a soft brush attachment, air-blowing with a photographer’s hand blower and ‘airbrasive’ methods, may achieve the desired result without involving potentially damaging liquids. Airbrasive methods involve the use of fine cork or powdered walnut as abrasives.
Chemicals have been used to etch surfaces, to improve the appearance of coloured crystals and to remove unwanted mineral species. Such treatments are not generally recommended and if necessary, as preparation for scientific examination for example, should only be carried out by specialists. The potential loss of information and the risk of long-term damage to the specimen outweigh the usually sought after benefits of these processes.
Repair and Consolidation
The nature of the sample and the reason for the repair will determine the type of repair technique and the adhesive used. Do not use very strong adhesives such as polyesters, cyanoacrylates (‘superglues’) and epoxy resins to repair minerals (King 1992c).
Repair techniques and suitable adhesives for the repair and consolidation of stone are described earlier in this chapter. A summary of commonly used adhesives, their constituents and features of their application is provided elsewhere (King 1992c). Note that any materials used to consolidate stone materials should have similar thermal expansion properties to the stone in question. If not, differential thermal expansion could result, leading to significant damage to the object.