Re: haunted GUM (related to judy's favourite pet peeve: the pigmentratio test)
phritz, you've got the right idea about different pigments requiring
different amounts to achieve a color-saturated layer; pigments vary
widely in pigment strength, as you're learning. Most earth
pigments, like your burnt siena, are quite weak as pigments go, so
it's not surprising that you don't get an opaque coating with a fair
amount of burnt siena (also, some burnt sienas are quite transparent).
The main comment I want to make in a hurry is that underexposure is
not likely your problem. If your strip were "severely underexposed"
the gum coating would dissolve into the water within a few minutes,
leaving you a piece of white paper to dry and try again. Since you
have it even where there's no exposure, that suggests stain rather
than overexposure as the source of the problem. Also, where you've
wiped off the bulk of the pigment layer on the area that received no
exposure, there's still significant stain left (that grainy deposit,
that's pigment stain.) Too much pigment, it looks almost certainly.
But there are a couple of things that don't make sense to me, so
maybe a clarification: I'm reading that this is one part of a sheet
you coated and tore into three pieces, and the other two pieces
printed fine? Could we see those? It doesn't make sense that with
two parts of the same coating on the same paper it printed fine and
with one part there was serious stain, so maybe I'm not understanding
your description/example/question.
But definitely not underexposed, if you've got heavy tone like that
that won't go away in 20 minutes of development.
There's an example with lamp black on my pigment stain page that
looks a lot like yours, down towards the bottom of the page, compared
to how it prints with half the amount of pigment. (third visual down
on the page).
http://www.pacifier.com/~kthayer/html/stain.html
Hope any of that is helpful
Katharine
On Oct 5, 2009, at 4:28 PM, phritz phantom wrote:
hi all,
my gum is acting strange again. the only reason i can think of is
an increased pigment load.
my standard pigment is lamp black, which is a very strong pigment.
0.5gr are enough for a very thick and opaque layer (before
exposure). since i was used to this strong pigment, i was generally
using too little pigment for all the other colors, resulting in
very thin layers. so, i made a comparison sheet with dabs of all
the different pigments (all are powder pigments) in various
strengths. i was quite surprised to see that for example 2gr (+5ml
gum + 5ml saturated pot-di) of my burnt terra di siena produces a
coating that is neither thick, nor opaque.
at first everything went fine, then suddenly a very thick blue
black coating (1,5gr iron oxide black + 1gr phthalo blue +5ml gum +
5ml pot-di) didn't come off at all during development. ok, i
thought the reason was that i increased the exposure time as well
to compensate for the bigger amount of pigment. later: the same
with a short exposure of 1 minute. the next day: again, with a
layer with 2gr of burnt siena.
it was time to search for errors. i coated a sheet with 1,2gr of
iron oxide black (not my favourite pigment), again with 5ml gum +
5ml pot-di, ripped it in three parts and made a comparison of the
two different sheets of glass i use as printing frames and put the
third one for 10min under the desk lamp that i often use during
registration and such. the first two printed fine and pretty much
the same. but with the third one, i noticed something strange. not
only that there seems to be some uv present in the light of the
desk lamp, but also: i left part of the sheet covered and it
received zero exposure. and this part stayed completely black, not
a whiff of pigment came off in the appr. 20min of development.
here's a scan of the test strip:
http://i31.photobucket.com/albums/c367/phritz/teststrip.jpg
the part on top with the white stripe received ZERO exposure. i
scratched off a little bit to show that the pigment is wet and
soaked. it can be removed, it just doesn't want to come off on its
own (nor did i have any success with brushing or sprinkling of
water, only nothing or everything comes off)
i'm sure this is somehow related to my problems. i'm just getting
too confused here. it probably means that my images were severely
underexposed. i did extensive testing for negative colors lately
and determined with a step wedge (unfortunately not a stouffer one)
that my minimum print time is 50seconds. i printed the thick layers
with up to 2:30min. still nothing.
(sorry for my total inability to write succinctly in english... my
apologies)
can anyone put some sense in this? i'm completely lost. any tips,
except trying even longer exposures?
thanks,
phritz
