This part of ISO 9022 specifies methods for the testing of optical systems, instruments containing optical components, and materials for optical instruments, under equivalent conditions, for their ability to resist mould growth. However, complete instruments or assemblies are only tested as specified in this part of ISO 9022 in exceptional cases. Normally, representative specimens such as mounted optics, material samples, or surface coatings on representative samples are used for testing. The tests described are designed for the selection of materials and components for instruments likely to be used in an environment that is conducive to mould growth, rather than for regular production control. The purpose of testing is to investigate to what extent the optical, chemical, mechanical and electrical performance characteristics of the specimen are affected by mould growth. In addition, the tests are designed to assess to what extent metabolic waste products (such as enzymes or acids), excreted by fungi, cause etching, corrosion, or short-circuits on, for instance, printed circuit boards.