At 1999/12/20 01:20 AM -0500, you wrote:
> >Both solutions are somewhat alkaline, and will slowly etch glass.
>
>Is there any harm to the glass or contamination of the solution from the
>process?
The resultant product is a very weak sodium or potassium silicate, which
does not normally affect photographic quality. In any event, glass is
better than plastic as glass is impermeable to gasses, which can affect the pH.
> >Either will absorb carbon dioxide from the air, and gradually increase in
> >content of the respective bicarbonate (e.g. sodium hydrogen
> >carbonate, aka sodium bicarbonate).
>
>Does this cause the pH of the solution to decrease or increase?
Decrease, but because the bicarbonate has a buffering action, there should
be no photographic effect unless the solution is kept for an extremely long
time. (As noted above, in glass the absorbtion of atmospheric gasses is
trivial.)
Also note that sodium or potassium carbonate not in solution also can
absorb carbon dioxide to a more damaging extent, if not kept in gas-tight
containers.
Sil Horwitz, FPSA
Technical Editor, PSA Journal
silh@earthlink.net
Visit http://www.psa-photo.org/
Personal page: http://home.earthlink.net/~silh/
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