On Thu, 19 Jan 1995, John B. Bunch wrote:
 
> I have soaked old photographs in a tray of
> water with a pinch of baking soda with subsequent rinse.  I
 
>         Question:  is there a better, readily availalbe
> chemical than baking soda to neutralize the ph?
 
To attack the easier question first, as Jim Druzik and Jack Thompson have
already said, calcium- or magnesium-based alkalizers are more conventional
in paper conservation.  There are numerous commercially available options
for aqueous or non-aqueous "deacidification."  The real question for
conservators who are largely self-trained (I assume you are among them) is
not how, but *if* to deacidify.
 
Jack has already given you the reason not to alkalize gelatin emulsions
(and the reason you need to know what is and isn't a gelatin-based emulsion).
There are other media (e.g. cyanotypes, blueprints, pigments...) that
also react to alkaline environments and should never be alkalized, even by
washing in naturally alkaline tap or distilled water.
 
I think I'm safe in saying that conservators seldom alkalize works of art
(i.e. your etching) unless there's an overriding good reason.  (Paper
conservators please comment?)  Some don't even wash them, because simple
washing is actually a non-reversible treatment.  Water and other chemicals
can cause distortion of the paper sheet (we recently saw a large albumen
print change dimension by about an eighth inch in one dimension when
washed gently).  Storage or appropriate framing in a neutral or buffered
environment is usually considered to address the problem of slowing
deterioration via acid mechanisms in art on paper.
 
Again, for the self-trained conservator, good mechanical support in
storage (folders, envelopes, mats, boxes, etc.) is a safer strategy even for
photographs mounted in or on brittle, acidic board (if that's the
concern).
 
Karen
 
P.S., Jack was right, this is the kind of question I try to answer.
_________________________________
 
Karen Motylewski                                508-470-1010
Northeast Document Conservation Center          508-475-6021 fax
100 Brickstone Square                           <[log in to unmask]>
Andover, MA 01810                               Use KM in subject field