RE: Clearing of Gum Bichromates

Mac Cosgrove-Davies 33121 (MCOSGROVEDAVIES@worldbank.org)
Wed, 10 Jan 1996 20:16:55 +0000 (GMT)

Mike wrote:

>The coloration of dichromate is intrinsically very intense -
>so if you can't see it (in an unexposed region), there ain't
>much there to worry about.

>The chemical effect of 'clearing' by (meta)bisulphite is to
>reduce the yellow chromium(VI) of dichromate to chromium(III)
>which is blue-green and much paler by comparison. So the
>chromium is not removed by the clearing agent, just made less
>visible. It would seem better to wash it out if you can. It
>also seems to me likely that residual dichromate will be
>slowly reduced to chromium(III) by constituents of the paper
>anyway..

This answers my question regarding clearing, but raises
another: is there anything to "worry about" if I don't remove
the dichromate by extended washing? What, if any, are the
long-term effects of either chromium (VI) or chromium (III) on
a gum print? Is one more stable/less damaging than the other?

Mac