I have used leather on Duo-Art pumps, both the box type and the steam-
boat style.  There are advantages and disadvantages, but generally
I think that a very good quality of heavy pump cloth is better.

The leather must be of excellent quality and/or much must be wasted
to avoid using the weaker and porous sections.  It also has to be quite
thin in order to allow for the folded areas to fit within the allowed
spaces.  Unless the leather is heavily finished it will leak, and it
may need to be sealed to achieve the original pump capacity.  If it
needs to be resealed this will be difficult in a box pump.  A leather
that is heavily finished to begin with will probably crack at the
creases in pump service.

It has to be considered that [today] this is not the era of industrial
leather.  Using anything other than kangaroo leather or very good up-
holstery leather would probably be regretted.

Spencer Chase