Harris hematoxylin is oxidized with mercuric oxide. Mayer type hematoxylins 
(such as Gill's) are oxidized with sodium iodate. (Some commercial 
hematoxylins are oxidized with more esoteric materials such as singlet 
oxygen.)

Manufacturers and vendors have abused the term "Harris hematoxylin", which 
now seems to mean "any alum hematoxylin formulation our marketing director 
wants to call Harris". Good Management, bad science. Read labels carefully.

Is there now any good reason to prepare hematoxylin with mercury for any 
purpose, or should this venerable formula, now creating an unacceptable 
environmental hazard, be retired?

About thirty years ago I was unable to make the Engel-Cunningham variant of 
the Gomori one-step trichrome stain demonstrate type I and II fibers in 
frozen sections of human skeletal muscle, until I substituted Harris 
hematoxylin for Mayer's. Adding a calculated equimolar quantity of mercuric 
chloride to a Mayer's formula made it work. I checked with Guy Cunningham at 
the NIH at the time, and he was using Harris hematoxylin. (Does anyone on 
this list know if Guy Cunningham is still living?)

(That's Richmond's hematoxylin, by the way, should anyone care to try it. ;-)

Note about spelling in this day of search engines: North America writes that 
hematoxylin is oxidized to hematein, while the rest of the English-speaking 
world oxidizes haematoxylin to haematein. (The blood pigment hematin/haematin 
is something else again.)

Bob Richmond
Samurai Pathologist
Knoxville TN