On Tue, 21 Mar 2000, Marlene F. LEFEBVRE wrote:

> Dear Friends. We are attempting to become GLP compliant, and was wondering
> how others handled expiry dates on the dry powder biological stains which
> in most part are very stable.  Help would be appreciated. Thanks Marlene

  Studies done at the Biological Stain Commission's lab have shown that
  dyes are extremely stable in dry powder form. See
  Emmel, V. M. and Stotz, E. H. 1986. Certified biological stains: a 
     stability study. Stain Technol. 61: 385-387.
  More recent investigations (reported at the Commission's annual
  meeting 2 years ago, but not otherwise published) confirmed these
  observations and extended the time for another 10 years.

  Thus, you could safely put an expiry date 10 years in the future
  on solid stains. The only exception might be alcian blue, which
  can sometimes change unpredictably into insoluble copper
  phthalocyanine. I don't think this change is related to time
  of storage, but suspect it is due to factors like dampness
  or accidental exposure to ammonia fumes.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1