Fungi and actinomycetes developing on historic objects
at elevated humidity not only actively attack the substratum
but may also sporulate profusely. This results in the formation
of extensive, diversely coloured stains, which mask the
outline of representational detail, making the whole object
illegible. When microorganisms form coloured sporulating
colonies on old photographs, portraits and religious objects,
where they colonize in particular light coloured places (including