It is a regrettable fact but a fact nonetheless that using almost any kind
of artifact or collection object also uses it up.  Some media, such as oil
painting, are remarkably enduring and give conservators little tsuris;
others such as anything on paper hate exactly the light that make them
visible.  Curators know that every minute of exposure, and the better lit
the worse, of a watercolor today is a minute denied future generations.
Display of anything entails probabilistic risk of theft, damage, etc.  The
economics of finite natural resources, which attends to the rate at which
things should be _ used up_, a rate that is never zero, apply to museum
collections, and the implications are unsettling to curators whose
professional culture is to save and protect stuff.