>what is the contribution of the tartaric acid? An old photographic
>chemical dictionary says it is used "as a preservative for sensitized
>paper and in emulsions." Obviously here it is being used in an
>emulsion; is it needed to preserve the image? Does anyone have any
>experience using the formula without the tartaric acid?
Without the tartaric acid, you will get a substantial precipitate of silver
citrate, which wastes silver and makes proper coating difficult. It has
nothing to do with preserving the image. The tartaric acid keeps the silver
in solution.
>Since tartaric
>acid is obtained from potassium hydrogen tartrate (cream of tartar),
>I am also wondering whether it might be possible to use this as a
>substitute.
It might be worth a try,it depends whether this substitute is acidic enough
to prevent the precipitation.
>I also have some old baking powder which actually
>contains tartaric acid in addition to cream of tartar, and I could
>use that although I would have no idea of the amount.
To work with 'ill-defined' kitchen chemicals can be a waste of time - are
you sure this is *all* the baking powder contains?
>Another idea
>would be to substitute another organic acid such as acetic, citric,
>or oxalic.
Citric and oxalic acids will increase the precipitation; silver acetate is
more soluble, but there is less tendency to complexation:- if acetic acid
works I'd be surprised no-one has already hit on it.
Good luck
Mike
Dr. Michael J. Ware
email: mike@mikeware.demon.co.uk
snailmail: 20 Bath Road, Buxton, Derbyshire, SK17 6HH, UK
phone and fax: +44 (0)1298 78604