The acids secreted by colonies of microscopic fungi cause
serious damage to chalk-rich grounds in easel paintings.
They also have a highly destructive e2ect on cellulose materials,
which under wet conditions are subject to acid hydrolysis.
This shows up during decay of paper and tissue; they
become thinner and weaker and also loose colour. In painted
murals and parchments the acids secreted by microorganisms
can bring about a weakening in structure despite the
protective e2ect of the chalk contained in them.