John Tuttle asks how to test the sealants fairly.  I think that
each sealant should be applied to give its optimum performance, taking
into account any resulting stiffness of the leather.  After all, in
practical use we will apply it so that it is as effective as we can
make it without affecting the suppleness of the leather.  If one is
difficult or time consuming to apply to get to its best, then perhaps
that should be mentioned.

It might be worth putting aside the test samples at the end of the test
and revisiting them a few years later to see if they have deteriorated.

James Black