U of S | Mailing List Archive | alt-photo-process-l | Re: haunted GUM (update)

Re: haunted GUM (update)

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.


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.

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):

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)

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:

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.

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.

judy, i will check out the archives and PF later today.

phritz phantom schrieb:

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.


Paul Viapiano schrieb:


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?


----- 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. 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?