John,
As we've all seen from Karen's posting, the term "old photographs" covers
a lot of territory.  Photographs represent a high order of chemical and
mechanical engineering. Properly processed at the beginning, they are
very durable.  If we are only talking about common black and white
photographs on paper, stuck to old black photo album paper with library
paste, washing them free should not hurt them.  They were designed to be
processed wet.
 
However,(and this is a BIG however) if parts of the image (emulsion)
begin floating to the surface of the bath, it is convincing evidence that
mold had once started growing there.  Look at the photograph in raking
light, slowly and carefully.  If there are *any* dull spots which cannot
be attributed to abrasion or some other mechanical cause, the spots may
be evidence that mold growth had one started there.
 
Mold spores are around us all of the time.  If the relative humidity is
high enough, long enough, and the air is still, mold propogation will
occur.  On a photograph it happens this way (it's easier to understand in
a drawing, but...) a mold spore on the surface of the emulsion sends a
taproot down through the gelatin until it hits the baryte layer (this
mineral creates a level surface on the paper which permits the gelatin to
lay down smoothly, creating a smooth surface) and then it spreads out
before traveling back up to the surface of the emulsion to create the
mold bloom we recognize.  Now, if someone brushed that away, or if the
air became dry before the visible bloom occured, all you would see would
be a dull area.
 
When such a print goes into the wash, water travels down the *taproot*
tunnel and spreads out under the emulsion.  All of the emulsion swells up
during washing, and those areas swell out and away.
 
I remember visiting a historical society one day and being brought to a
back room where volunteers were washing photographs.  The volunteers had
just nicely discovered a bunch of floating heads, lifted out of a 1920's
class graduation photo.
 
There are no easy answers; only choices.
 
Jack
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On Fri, 20 Jan 1995, John B. Bunch wrote:
 
> Jack,
>         Thank you.  What would be a good
> chemical/recipe/procedure for old photographs that have been
> stored in highly acidic environments?  Maybe just several
> soak/rinse cycles in pure water?
>         Regards,
>         John Bunch
>         [log in to unmask]
>