>To Gummists
I find that if one washes a gum print in gently running water for six hours, it
will clear to the effect that there is no discernible difference in colour
between that of the print and my undichromated test swatches.<
This is no doubt correct for your test swatches but we do not know what
colour they are,however the stain is still there whether it is apparent or
not and is a fundamental component of the imaging system and which is not
necessarily a bad thing, this is what gives the soft tonal range, other
wise we would be dealing with a lith type image,it is just this combination
of a hard and soft tonality in the same emulsion, that invokes the
intriguing character of the medium.
Let me put this way if an emulsion consisting of gum and Dichromate alone
with no pigment included is exposed in step wedge fashion, the first
discernible tone will be a light beige colour, this colour will get slowly
warmer and darker in tone, with increasing exposure until a rich chocolate
brown colour is reached, when a kind of maximum black is reached,and
however one increases the exposure no further increase in density occurs
for the system has reached a maximum brown and stabilises. An image
which is very beautiful, I start with this exercise with my students when
we enter the world of the dichromated colloid.
It this image that underlies the pigment, however the the first tones on
the edge of underexposure can be lightened to a degree by using so called
clearing techniques, but as far as I know there is no method of actually
bleaching ,or dissolving this stain from the tones in the middle and shadow
regions.
To use the old saying a leopard cannot changes its spots but what can be
done is to arrange them in a more pleasing form.
this is just what the previously mentioned methods do, bisulphate or
metasulphate
will change the brown stain to a lovely soft green / blue grey, I have not
yet tried Terry extended wash but I seem to remember doing something
similar in the distant past by accident and got a result similar to the
metabisulphite method however I will try again, testing testing it never
ends !
It is not that I am green [ and who would say anything different in
these days of political correctness,] but lazy, my method is quick
and uses very little water. A 1% solution of sulphuric acid clears the
brown stain to a neutral grey, in two to three mins then a brief wash in a
dish, with three or four changes of water and *bingo* problem solved
I have said all this somewhere before, I am beginning to have some sympathy with
Judy it seems I have my head stuck down a well as well ;-)
pete