[Histonet] Problem with Vectashield Hard Set

[Monfils, Paul]

A couple of weeks ago I inquired about aqueous coverslipping media that
harden. Vectashield Hard Set was recommended by a few people. Then I
remembered that I actually had some of the product, which I purchased a
couple of months ago, in my refrigerator.  I tried it, and at first was very
pleased with it.  It seemed to have a refractive index closer to that of
glass than most aqueous products, and the resolution was excellent.
However, I am now finding that after being coverslipped for a couple of
weeks a large amount of air space develops, first immediately around the
tissue section, and eventually extending onto the tissue section.  This does
not appear to be the typical problem of air being drawn under the edges of
the coverslip due to evaporation of solvent, as there is no air space near
the edges, only on and immediately around the tissue.  Besides, the stuff is
supposed to harden overnight, according to the package insert.

Has anyone else encountered this problem?  What is the nature of the
problem?  Are the spaces actually air?  Or some evaporated component of the
product?  And any hints on how to deal with it, other than soaking off the
coverslips and recoverslipping?