U of S | Mailing List Archive | alt-photo-process-l | Re: haunted GUM (related to judy's favourite pet peeve: the pigmentrat

Re: haunted GUM (related to judy's favourite pet peeve: the pigmentratio 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. 40c/ 100f), 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:

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:

i think i'm losing my marbles here... we'll see how the test strips from today will print.


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).


Hope any of that is helpful

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:

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?