Re: plastic coplin jars

From:"J. A. Kiernan"

Your question raises several interesting points
concerning plastic staining vessels and silver

Kathleen Hollenbeck wrote:
> What is the best method that you have found to clean plastic coplin
> jars?  We do the Jones and Steiner in the microwave using plastic coplin
> jars.

Any deposit of silver (dark or mirror-like) must be
completely removed from a vessel before doing any 
other silver staining technique. Otherwise, silver 
will be chemically added to the deposit instead
of to the objects you intend to stain.

There are three simple solvents for metallic 

1. Conc. nitric acid. This is the easiest one
  for glassware, but not for most plastics,
  which will be oxidized (some with much heat).
2. A solution of sodium or potassium cyanide.
  Cheap, but not used in labs because of Agatha
  Christie. (Industrially it's used by the ton;
  it can be safely used and then made harmless,
  but who wants to convince the safety ossifer?)
3. Farmer's reducer, used by photographers to
  lighten or remove ("reduce") the dark parts
  of black & white negatives or prints. Chemically
  it is an oxidizing agent (ferricyanide) mixed
  with a complexing ion (thiosulphate). Neither
  of the ingredients is considered hazardous.

  A.  Sodium thiosulphate (Na2S2O3.5H2O): 25 g
      Water:                             250 ml
  B.  Potassium ferricyanide (K3Fe(CN)6): 12.5 g
      Water:                              125 ml      

  Add 6 ml of B to 100 ml of A before using.
  (In photography, the mixture is further
  diluted to 200ml. Increase the proportion
  of B for more rapid action.)
  This won't damage the plastic, but it may be
  too weak to remove the deposited silver. Safe
  chemicals, like safe fireworks, can sometimes
  be less than effective. [The "Burning Schoolhouse,"
  never a big thrill, is now housed in non-flammable
  cardboard, so it just sends sparks out of the
  chimney and doesn't burn at all. That's how it
  is in Ontario these days; perhaps it's better
  in Texas.]
The REAL ANSWER to your question is:
Don't do silver stains in plastic Coplin jars.
Get a few glass ones, and clean them with nitric
acid. Remember to rinse with pure water 2 or 3
times after the nitric acid. Tap water contains
chloride ions. Silver chloride is insoluble and
it is reduced (in the chemical sense) in daylight
or fluorescent lighting to colloidal metallic silver.
You can use plenty of tap water to wash away the
last of the nitric acid, but follow up with 2 or
3 rinses in pure water to expunge the chloride
that comes from the tap. 

Informed attention to the washing-up is one of the
keys to getting silver stains to work properly.
Another essential is to read through the steps of
the procedure (for some reason I can't bring myself
to call it a protocol) and be sure that you KNOW
THE REASON for each one. For example: In some methods
there are thorough washes in pure water between
immersions in the working solutions. In other
methods the slides are carried directly from a
silver-containing solution into a liquid similar to 
a photographic developer (a reducing agent in the 
chemical sense), in order to add some silver ions,
which are needed for the development (amplification)

In 1996 there was a special issue of the Journal of
Histotechnology devoted to silver staining. It made a
large amount of information available to U.S. histotechs
who get the journal but do not have access to libraries.
That special issue of J. Histotechnol. (Vol 19 No. 3)
contains the answers to many questions relating to silver
staining in pathology and other disciplines.  
John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London,   Canada   N6A 5C1

<< Previous Message | Next Message >>