Re: haunted GUM (update)
That all makes good sense to me, I apologize for assuming you must
have some Stouffer step wedges around. More later, ....
On Oct 7, 2009, at 8:21 AM, phritz phantom wrote:
hi katharine,
thanks for taking time to have a look at this mess.
i didn't expect the tonal inversion either. at first i printed with
the pot-di with the same times as the am-di, because i totally
forgot that i changed it (mixed up some time ago, same bottle, same
color...). then the non-clearing layers occurred. since then i'm
printing test strips trying to bring some sense into this.
i do have a step wedge, but it's made by kodak and even bigger than
the chart throb scales. also i only have one. i tried to get a
stouffer recently, but i there was only one store in germany left
that sells a step wedge and it's not made by stouffer. later i
contacted stouffer directly, but they don't accept paypal and i
don't have a credit card....so this was delayed until the future.
you're right about the 1:30, this was the time i was placing my
exposure times around. there is no use in trying to establish a new
exposure base time until i can get rid of the stain and the non-
clearing unexposed areas. you saw how my 2:30 and 4:00min exposures
look like.
ad 1)
same emulsion, same brush. only difference is that the newspaper
pics were taken with a digicam and not scanned like the others.
i wasn't aiming for an opaque layer, i just wanted to see how deep
i can get the shadows in one layer until i get flaking.
ad 2)
the "expectedly" was only because of the recent behavior . because
of the non-developing layers i saw earlier. it's not a one time
thing, it's repeatable.
i think the key to the riddle is finding out why unexposed emulsion
won't develop at all. or why it won't dissolve, it can be brushed
off quite well.
regards,
phritz
Katharine Thayer schrieb:
phritz, there's no reason why changing to potassium dichromate
from ammonium dichromate should cause tonal inversion, as long as
you're adjusting the exposure to accommodate the difference in
sensitivity. It's the dichromate ion that participates in the
reaction that hardens the gum, and that doesn't change; it's just
that if you've switched from saturated ammonium dichromate to
saturated potassium dichromate, you've roughly halved the number
of dichromate ions per ml dichromate (you could get the same
effect, roughly, by staying with ammonium dichromate and diluting
to half the concentration) which means you've reduced the light
sensitivity of the emulsion, therefore, you need more exposure.
Did you do some test strips to determine the new exposure when you
changed dichromates? Eyeballing the charts from the ammonium
dichromate tests, it looks like your best exposure there is about
1:30, so your best exposure for the potassium, depending on the
concentrations you're using in both cases, should be around 3:00
or so according to my test charts which show a straight linear
relationship between dichromate concentration and speed (one-half
the dichromate >2x exposure, one-third the dichromate >3x
exposure, one-fifth the dichromate> 5x the exposure).
Maybe I'm misunderstanding what you're doing here, but it looks
like you're printing ChartThrob charts to determine exposure.
Okay, but wouldn't it use a lot less paper just to use a step wedge?
Some random comments in random order:
(1) What a gorgeous burnt siena; it makes my mouth water. But why
does it look so gorgeous and transparent on the newspaper and so
dull and chalky on the test strips, at the same pigment
concentration?
If the pigment is as deliciously transparent as it looks on the
newspaper, you're never going to get an opaque coating layer with
it (this is referring to a comment you made yesterday about not
being able to get an opaque layer with the burnt siena) and to my
mind, that's a good thing. Also, an opaque coating layer isn't
necessarily something you want to strive for either; many gum
teachers recommend a layer that you can still read the text
through if you brush it onto newspaper.
(2) "expectedly, the two with heavier pigment load did hardly
develop at all, even after two hours" --that one has me baffled.
There's no "expectedly" to it; there's no reason for a print
that's printed with more pigment to take longer to develop, unless
it's been grossly overexposed in overcompensation for the heavier
pigment load, which I don't see any evidence of, as the exposures
are the same for the heavy pigment loads as for the light pigment
loads.
I have more thoughts but I'll send this for now and follow up
later. Thanks for sending all those; it sure helps having
something to look at.
Katharine
On Oct 7, 2009, at 6:22 AM, phritz phantom wrote:
hi all,
(quick recap:)
i recently switched from ammonium dichromate to potassium
dichromate, which i totally forgot. i think the pot-di is the
most likely reason for the trouble i'm having right now. i did
print gum with the pot-di before the mess, but this was on wood
and canvas only, and i force-developed each layer with a brush.
this is why i haven't noticed the new behavior earlier.
1st test strip (with explanation):
http://i31.photobucket.com/albums/c367/phritz/burntsiena1gr.jpg
this is with appr. 1gr of burnt siena (+ 5ml gum 16% + 5ml pot-di
saturated). you can clearly see the tonal inversion with the
shorter exposure times. on top there is a strip that was covered
with cardboard (covering the whole thing widthwise), that
received zero exposure. it is noticeably darker than the area
that received 1min of exposure.
similar result with lamp black (0.1gr)
http://i31.photobucket.com/albums/c367/phritz/lampblack01gr.jpg
expectedly the two ones with heavier pigment load did hardly
develop at all, even after 2 hours. again tonal inversion and
nothing coming off in the zero exposure areas.
2gr burnt siena: http://i31.photobucket.com/albums/c367/phritz/
burntsiena2gr.jpg
1gr iron oxide black: http://i31.photobucket.com/albums/c367/
phritz/ironoxideblack2gr.jpg
here's a pic showing the thickness of the emulsions:
http://i31.photobucket.com/albums/c367/phritz/coatings.jpg
and i dug up and old test strip from about 2 months ago, with the
same negative, same paper, same size, same mix of gum, same
pigment... only with am-di. this mix was 1gr of lamp black +10ml
gum/ 10ml am-di. exposure times start at 20sec and each grey
scale gets +20 sec, so it's from 20 sec to 3:00 min.
http://i31.photobucket.com/albums/c367/phritz/oldemulsion.jpg
i will try different papers and gum and pot-di in various
strengths next. hopefully there is a way out of this mess.
if anyone can offer some hints or ever experienced something
similar , it would be very much appreciated.
thanks,
phritz
ps.
judy, i will check out the archives and PF later today.
phritz phantom schrieb:
paul,
unfortunately i printed the negative, the one shown in the
second pic. that caught me completely off-guard and i took me a
day to realize what happened. it took a quick look first and it
looked normal with a lot of stain, then later i suddenly
realized it.
there is definitely something fishy.... i printed all the test
strips this evening and i constantly get the tonal inversion.
although not as extreme as the first time. AND another thing i
consistent: no exposure - no pigment coming off at all.
another thing just dawned on me: those are the first gum prints
i made with the new batch of potassium dichromate. i've only
used ammonium before. i totally forgot that i mixed up a fresh
solution about two weeks ago. i think this is the first time i'm
using it. most likely it's the dichromate that is somehow
responsible for this mess. i'm using saturated solutions, so the
exposure time should go up naturally. it still doesn't explain
the severe tonal inversion and stuff.
is pot-di more prone to fogging (from room light)? maybe this is
some kind of solarisation, i'm having here.
i've never been especially careful about room light, but i never
had problems before. i coat with the lights on, then dry in the
dark, but i occasionally turn on the lights for a minute or two,
when i need to use the bathroom (this is where the drying takes
place).
maybe the pot-di is on the phritz (!!) alltogether?
also i will try a different paper and a new mix of gum. maybe
the gum solution is foul.
the test strips are drying now, i will scan and post them online
tomorrow.
phritz
Paul Viapiano schrieb:
phritz...
The inversion you're seeing is weird, a positive of that chart
will always print with black text on white.
But you're printing the positive, right...you never inverted it
to print?
NOw, there's inversion that K speaks of on her site but that is
not TOTAL inversion, just a reversal of the high tones usually
because of gum/pigment ratio. I've experienced this once on a
test strip. I added gum and it was fine.
But a TOTAL reversal as you are claiming...well, I've never
heard of that at all.
Are you absolutely positive (no pun intended) that you exposed
the correct digital charts?
p
----- Original Message ----- From: "phritz phantom" <phritz-
phantom@web.de>
To: <alt-photo-process-l@usask.ca>
Sent: Tuesday, October 06, 2009 10:10 AM
Subject: Re: haunted GUM (related to judy's favourite pet
peeve: the pigment ratio test)
dear katharine,
yes, this is my main source of confusion. i was experimenting
with higher pigment loads. i made three layers of yellows and
reds (for the highlights) and then wanted to add the shadows.
i mixed up a stong emulsion (the 2.5gr blue black one) and
thought that the worst thing to happen is that the layer just
washes off and i can do it again. i tried the heavy load to
check the limits of the process, to see how far i can go with
the pigment concentration. the layer not dissolving at all,
that i was not prepared for.
i did this twice (i saved the excess emulsion from the first
coating). at first a 2:30 exposure and a 2-3h development, the
last hour in hot water (appr. 40°c/ 100°f), then i had enough
and brushed it all off. dried overnight and painted on the
same emulsion the next day. this time with only 1min exposure.
same result. no flaking, the emulsion did not move at all.
also when forcing the development with a brush, i did not see
the usual high-contrast image (the highlights coming off
before the shadows which got lots of light), it just came off
all at once.
then i coated the test sheet with the 1.2gr of iron oxide. and
saw the pigment in the unexposed area behave the same way as
the emulsions before. this makes me assume that there is some
kind of connection. i just don't know which one.
....
i just wanted to type that the test sheets "printed with a lot
of stain, but in a way like i expected them to", then i
started wondering why the "stain" is happening in the areas
that should be pitch-black, because they are in the clear
areas of the transparency. now, i went and had another look at
those and saw that they are completely INVERSED. i printed
negatives from a negative (i did NOT forget to inverse the
scale in photoshop).
here are the scans:
http://i31.photobucket.com/albums/c367/phritz/threestrips.jpg
the one on the left and the one in the middle got 1min
exposure (all three scales the same) from my sunlamp. the one
on the right got 10min of desk lamp.
here's the proof for the inversion:
http://i31.photobucket.com/albums/c367/phritz/P1010035.jpg
i think i'm losing my marbles here... we'll see how the test
strips from today will print.
phritz
Katharine Thayer schrieb:
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
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