[Histonet] Glass cleaning for silver

[John Kiernan]

Rosemary Behan <rosemarie_g_behan <@t> groton.pfizer.com>
asked about cleaning glassware
for silver staining. 
A reply follows.

It's necessary to remove traces of metallic silver,
which are not necessarily visible. The only common
acid that does this is nitric. Here is what I do,
with rationale. Let's assume the vessel is a Coplin
jar.

Rinse with one or two changes of distilled water.
  [Tap water contains chloride ions and silver 
chloride precipitation must be avoided.]

Pour a few ml of concentrated nitric acid into
the vessel and carefully let it wet all the
inside surface. For a Coplin jar it's important
to dissolve silver from all corners and from the
slots for supporting slides. It takes 15-30
seconds to make black deposits or mirrors 
disappear. A minute of turning and tilting has 
to be enough to remove all the visible and
invisible silver.

Safely discard the nitric acid and fill up the
vessel with distilled or otherwise purified
water, three times.
  [Pure water must be used because tap water
will precipitate traces of silver chloride
from the residual nitric acid - which contains
dissolved silver nitrate.]

Wash in tap water, detergent etc as for any
other dirty lab  glassware, and don't spare the
brush.
  [The nitric acid treatment does not remove
all types of dirt. Bits of detached section,
stuck to the glass, are made yellow by nitric
acid.]

Rinse in tap water, repeatedly, to get
rid of the detergent (no more froth with
shaking) and then in 3 generous changes of 
pure water to dilute out residual chloride
from the tap water.
  
Let the vessel dry by drainage and evaporation,
then keep it in a closed cupboard, with its
lid on (if it has a lid; and don't forget to
clean the lid).

If glassware is contaminated by insoluble silver
compounds such as silver chloride, 5% sodium
thiosulphate (10 minutes) will remove the silver.
  [The thiosulphate ion strongly complexes silver
ions and will remove them from solid silver 
halides. This is the "fixation" of photographers.]

In the above remarks I have not given detailed
safety and disposal instructions. Conc. nitric acid
is nasty stuff but becomes harmless when diluted
with water.

Do not use hydrochloric acid or an HCl-alcohol 
mixture for "acid washing" of glassware that will
contain silver nitrate or protargol. 
  [Reason is obvious from above discussion.]

There are silver solvents less noxious than 
concentrated nitric acid. The best known one is
Farmer's reducer. This is used in black & white
photography for controlled removal of darkness
(= silver) from negatives or prints. It is a
solution containing potassium ferricyanide and
sodium thiosulphate. Its actions on photo media
take several minutes, but it takes much longer
to weaken silver deposits on glassware and in
overstained sections (my unpublished anecdotal
observations).  

For what it's worth, I think concentrated 
nitric acid is the best cleaner of glassware 
used for silver methods. I also think that
poor glass-hygiene (dishwashers etc etc etc)
often causes failure or poor results with
many staining techniques.
-- 
-------------------------
John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London,   Canada   N6A 5C1
   kiernan <@t> uwo.ca
   http://publish.uwo.ca/~jkiernan/
--
(Rosemary Behan: I've deleted many irrelevant 
messages from the tail of your email, which 
contained a megabyte of unrelated stuff. 
Please be careful about what to quote!) 
_____________________________________
"Behan, Rosemarie G" wrote:
> 
> I am looking for a recipe for acid cleaning glassware to do silver stains,
> can anyone help me?
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