Bleeding gumovers

sdivot · Jan 10, 2008

Hi,
I'm doing gumover platinum, and while they look good, I'm getting bleeding of the gum layer.
I know that I can alleviate this by giving more exposure, but I'm trying to get color just in the shadows and partly in the midtones. More exposure will drive color into the highlights.
I do my development (30 minutes facedown in water), and then rinse the print for a few seconds to a minute or so. It seems as if the print is fine, but it tends to bleed when left for a few minutes.
What's the secret to stoppping the bleeding? How can I vary my exposure times to get color into different areas of the print without getting this bleeding?
Anyone, anyone?
Thanks,
Steve

Kerik · Jan 10, 2008

I think you need longer exposure. It sounds like you're not hardening the gum enough, even in the shadows, if you're still bleeding after 30 minutes. Try longer exposures and cutting back on the amount of dichromate to shorten the scale and help keep the color out of the highlights.

sdivot · Jan 10, 2008

Thanks Kerik,
I'll give that a try. I was afraid that lowering the dichromate load would cause even less of the pigment/gum to stick, but I think I get what you're saying.
The less dichomate, the less sensitive the mix. So the tonal scale will be shorter.
I still need to give enough exposure to harden the gum though.
Right?

So, would I be better served to stick with a more or less standard exposure time, while varying the dichromate load to get color into different areas?

Steve

Katharine Thayer · Jan 10, 2008

Ah, the dance of the variables. I've just been working on a web page with that title today, about these complicated interrelationships among variables in gum.

I agree with Kerik both that you need more exposure (given the same amount of dichromate) if you're losing gum not just in the highlights, where you don't want it anyway, but also in the places where you do want it to stick, and that if you don't want color in the highlights, one way to do that is to reduce the dichromate (which would increase contrast by dropping out highlights). However, if you reduce the dichromate, you will need to increase the exposure even more in order to retain the gum in the shadows and midtones, since speed is a direct function of dichromate concentration. Hope that makes sense,
Katharine

scootermm · Jan 10, 2008

I learned my gumover pt/pd through Kerik (somewhat circuitiously) and Clay Harmon, so more than likely Kerik's comment about +exp and -Dichrom is going to be helpful...
With that said, and for what its worth, I had similar bleeding and found that also washing the print in a gentle bath for a longer period of time helped immensely in lessening the bleeding. Usually Ill "develop" in a tray of water for 20mins then put that "developed" print in the washing tray for the entire 20 mins of my next gum development. It seemed to help me lessen bleeding a great deal.

Kerik · Jan 11, 2008

Matt - Doesn't that just mean you are developing for 40 minutes instead of 20? I like to balance my exposure, gum/dichromate mix and exposure such that I'm done somewhere between 15 and 30 minutes of development (ie no more bleeding or running).

scootermm · Jan 11, 2008

yeah, basically it means its 40mins of developing.
just seemed like a mere min or so of rinsing wasn't quite enough (given what sdivot mentioned).

sdivot · Jan 13, 2008

My prints are still bleeding.

Here's my process: I'm using Christina Anderson's method from her book.
1 Part gum/pigment stock mixture (mix is 1 tube watercolor with 50ml of gum)
1 part gum
1 part water
1 part saturated am. dichromate
This had worked before. Using 40-60 units of exposure in my NuArc unit, I was getting color in the shadows and midtones. Little to no bleeding with 30 minutes of development.
I was happy.

Now, my prints are bleeding. So, after the advice, I reduced the dichromate by half. I replaced half of it with water.
I have gone from 80 units, to 120, to 160 units of exposure time. Still bleeding, and if I rub the print (after deciding to start over), pretty much all of the color comes off. A little color sticks when I went to 160 units of time.
Oh, and I'm getting some flaking off in some areas of the print.

I can't figure out what's changed.

My straight gum prints (I'm in the process of calibrating the PDN system for 3 color gums) seem to be fine. No bleeding.

Any ideas?
Thanks,
Steve

Akki14 · Jan 13, 2008

Adding in water changes the ratio again, so don't dilute the dichromate (essentially what you're doing) and try again?

clay · Jan 13, 2008

As Katherine pointed out, this is a multi-variable problem. I do pretty much what Kerik says, and aim for my developing to take about 20 minutes in 75 degree water. So in essence, that is fixed. The other two non-pigment coloration related variables are the exposure time and the dichromate concentration. If you want 'better cemented' gum layers, this requires longer exposure times but shorter scale. So you would then back off on the dichromate concentration. I would suggest doing some test strips with a wedge to see what you get with this. Try using half the ammonium dichromate at twice the exposure. Likely to be too much, but you will see which direction this combination of variables moves you.

It is doable. FWIW, I did my 40 prints for my last show consisting of 2-3 layer gumovers with masked, paper white borders surrounding the images. So it is possible.

Katharine Thayer · Jan 13, 2008

sdivot said:
I can't figure out what's changed.

My first guess would be that your workspace isn't perfectly climate-controlled and the humidity has changed. If it's drier now than when the identical protocol was working before, that could explain the difference, as there's a strong relationship between ambient humidity and speed of the gum emulsion if other things are held constant. I have mostly worked in a rather humid environment, but a few unusual times when the humidity has plummeted, I've found that even 5 or 6x the usual exposure for a particular emulsion isn't enough to keep the gum from washing off the paper in development.

My straight gum prints (I'm in the process of calibrating the PDN system for 3 color gums) seem to be fine. No bleeding.

If you're saying that you're using the same formula and same exposures for the gumovers as for the straight gum, under the same environmental conditions, same paper same light, same everything, but getting different results, that doesn't make sense, I agree. The mechanism of gum hardening should be operating the same if the emulsion and other variables are the same, regardless of what you're printing the gum over (platinum, paper, or gum) as long as the paper and treatment are the same. If the paper or treatment of the paper are different, then one wouldn't expect the exposures necessarily to be the same; they'd need to be calibrated for the different protocols.
Katharine

Kerik · Jan 13, 2008

For your straight gums are you pre-treating the paper in any way? Are you sizing your gumovers or straight gums?

sdivot · Jan 13, 2008

Kerik, I preshrink and size the paper for the gumovers and straight gums the same way. Gelatin, formalin, etc... I suppose something funky could have happened with the sizing step for these two particular prints I'm having trouble with. But it doesn't seem likely, since I sized a bunch of other paper at the same time.

Katherine, I live in Houston, TX, so the humidity should not be a problem. I know it is drier in the winter, but the gumovers that have worked were done recently enough (in december) that I don't think the humidity has changed much.

FYI, I am using the same digital negative (with a PDN pt/pd curve) for the pt/pd and the gumover part. It may not be ideally curved for the gum layer, but again this was working before.

I think I'll do what Clay suggested and just back up and do some test wedges.
Very frustrating...

Thanks for all the replies,
Steve

Katharine Thayer · Jan 13, 2008

sdivot said:
I think I'll do what Clay suggested and just back up and do some test wedges.

clay is right; it's the only thing to do under the circumstances. Good luck,
kt

Bleeding gumovers

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