I can't find where I first saw this, but in the first recipe of subbing
solution that I used in the '60's (when developing my protocol for
autoradiography) EMPHASIS was placed on the use of 'fresh' chromium
potassium sulfate.  "Fresh' meant insuring that the crystals were
predominately purple and clear.  Too much white was a bad sign.  I have had
a one pound jar of this substance for many years, and if I had to make some
subbing solution now, I would have to first rinse and then dry a measure of
the crystals to insure that they satisfied that old concern.

I have not seen this mentioned in the many recipes for subbing solution that
I have seen on the web.

Also, having checked my original offering on this subject, I see that I used
the color lavender, which is the color of crystals of Ferric Ammonium
Sulfate that one must use to make 'good' mordant for Iron Hematoxylin
procedures.  Sorry for that mistake.  The color of chromium potassium
sulfate crystals are moderately deep purple, though my color discernment is
always open to some interpretation.

Hope this helps some.

Fred Monson

Frederick C. Monson, PhD   
Center for Advanced Scientific Imaging
Schmucker II Science Center
West Chester University
South Church Street 
West Chester, Pennsylvania, USA, 19383
Phone:  610-738-0437
FAX:  610-738-0437
fmonson@wcupa.edu
CASI URL:  http://darwin/wcupa.edu/casi/
WCUPA URL:  http://www.wcupa.edu/
Visitors URL:  http://www.wcupa.edu/_visitors/