On Sun, 15 Oct 2000, Lee & Peggy Wenk wrote:

> Does it matter what order the reagents are added together to
> make an aluminum salt-sodium iodate hematoxylin, such as
> Mayer?

  No.  The iodate oxidizes the haematoxylin to haematein,
  which then forms a dye-metal complex with aluminium ions. The
  complex (with excess aluminium) is the staining reagent.
  Aluminium salts do not interfere with the oxidation of 
  haematoxylin to haematein, so you can just chuck everything
  in and leave it on a magnetic stirrer until everything has
  dissolved. 

  I like to dissolve the haematoxylin and iodate first (because you
  can see that they have dissolved) and put the alum in last, but
  this isn't necessary. For an air-ripened mixture such as Ehrlich's,
  the alum and other ingredients all go in long before any of the
  haematoxylin becomes oxidized to haematein. 

  For a long life, only part of the haematoxylin should be converted 
  to haematein by iodate (instantaneous) oxidation. This leaves a 
  reservoir of haematoxylin that is air-oxidized to haematein over 
  the course of several weeks, to replace the haematein lost by 
  further oxidation (to useless products) and also that which is 
  removed from the solution by uptake into stained sections.

  These stains should really have names like "Harris's haemalum," not
  "Harris's haematoxylin" because haematoxylin does not contribute to
  the imparted coloration. It is the precursor of one component of the
  haematein-aluminium complex. The idea of adding only enough iodate
  to oxidize half the haematoxylin (thus prolonging shelf life) is
  quite modern (about 1950 I think). The early authors prescribed
  enough oxidant to change all the haematoxylin into haematein,
  except in the case of the slowly ripening air-oxidized formulations,
  which still have the best keeping properties. The name "haemalum"
  has been around for many years, but doesn't seem to be much used
  in North America. It nicely takes care of all solutions that contain 
  haematein or a mixture of this dye with haematoxylin.

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