Gum prints and humidity
i'm a fairly new gum printer and have been mostly experimenting different papers, combinations and techniques for now.
I am trying to write down everything as much as possible to be able to get consistent results, but somehow in april after a successful set of prints and a two-weeks holiday, I wasn't able to produce a single print worth keeping. Everything was going wrong (either way all of the emulsion was dissolving or almost none, during development). I didnt change the kind of gum, nor its concentration, nor the paper, nor the exposure distance / times, negatives, pigment, everything was the same !
Then I found a mention about ambient humidity having a huge impact on printing results on Katharine Thayer's website. So I decided to wait until the weather and air gets not so dry to resume printing.
Strangely however, now that humidity is almost back at the april's level, I'm still getting 3/4 of bad prints, and very inconsistent results from print to print ...
What could cause such a situation ?...
Xandros, I take it you live somewhere where it's drier in the summer than in the spring and fall? Do you have a way of measuring the ambient humidity?
If you're really not changing anything from print to print, the results should be consistent from print to print; the fact that you're getting very inconsistent results suggests that perhaps everything isn't remaining constant from print to print. If you're getting inconsistent results on the same day, in roughly the same ambient conditions, it's unlikely that it's humidity that's the problem; I'd start looking elsewhere. The problem you describe, "either all of the emulsion was dissolving or almost none, during development" suggests erratic exposures; what's your light source?
It can be frustrating when things aren't going right, but working carefully, changing one variable at a time and taking notes, should quickly lead to a more consistent practice. Good luck,
Gum Prints and Humidity
First, I agree with Katharine she really knows what she is talking about. I, on the other hand am a Gum newcomer with about ten months experience. At the beginning of my gum work I found myself often experiencing what you are, that is I kept very careful records, I tried to change only one variable at a time and despite my most careful working methods the process often seemed unmanageable. As I struggled along month after month patterns slowly did begin to emerge and I slowly grasped the "dance of the variables" that Katharine refers to. What I kept in mind was that other people are making nice gum prints and eventually I should be able to also. It seemed to take forever, but through experience and much practice, careful note taking and by changing only one variable at a time I am now beginning to get the prints I had hoped to .
I don't know if humidity is the key issue with your prints or not. It may not be. Still, I can tell you what I do about humidity. I obtained a sling psychrometer. It is a old fashioned but reliable way to test humidity in the room you are working in. I test and record the humidity each time I print. In my workroom my baseline humidity was 65%. Through experience I found that for each addition or subtraction of 20% humidity I add or subtract one stop worth of exposure. So if the humidity is 45% I add one stop worth of exposure, making a three minute exposure six minutes.
Unfortunately I can not say that what I am doing will work for you. My results only apply to my workflow in my geographic location. You will have to observe your own results to see if my experience is applicable to your situation.
Ultimately my advice is quite the same as Katharine's. The only thing I might add would be that it is really hard to learn to make gum prints but gum eventually does reveal its secrets to those who pursue it. The reward is being able to make one of the most subtle and beautiful kinds of photographs ever invented. Good luck!
Xandros, listen to Katharine -> if you're getting inconsistency the same day (w/o major climate change), then probably it's not about humidity...
OTOH, just for the records, if you want to eliminate humidity parameter from your workflow you can do like I do:
Coat, wait 5 minutes, dry with a hair dryer (be gentle, dry on low heat just until the surface isn't tacky anymore, not more), then humidify using an ultrasonic humidifier. (Mind to be consistent on your humidification ritual!) You'll get very consistent results all year round...
Thanks for your answer Katharine. I learned a lot of what I know so far on your website, btw.
Anyway, the thing is, I kept ALL variable exactly the same. They worked for 2 different negatives, then 2 weeks later one of those negatives almost all the time seems underexposed (all washes out) and the other overexposed. It's a a bit inconcsistent but generally speaking i'm getting the same king of bad result for each negative.
I bought an electronic hygrometer and fond out that even though i'm in Belgium (quite wet overall), the humidity can drop from 70% when it's very rainy for a few days to about 35% when it's sunny for a week ...
I maybe could do a series of tests to build a humidity / exposure curve ?... dunno if it's worthwile.
I also experienced different behaviour when the sizing has been done at high humidity level or low level, not only exposure. Looks like when humidity is low, the gelatin sizing does not have the time to soak into the paper's fibers and just dries at the surface, and it doesn't work so well for printing afterwards...
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You don't seem to have noticed my description about how you can rule out the humidity parameter from your workflow??? It's not worthwhile if you work as I describe before; the moisture level in paper / exposure times will be always comparable with that method.
Originally Posted by Xandros
Do you work the sizing "in" the paper with a brush? I have sized in every possible indoor environment in my place (from 18C/30% to 28C/60%, BTW please note that RH figure isn't enough to tell us the absolute moisture content of air unless stated along with temperature...) and never noticed any, again any, difference in results. I use a "foam brush" and "work the sizing in the paper" brushing the "hot" (50C) gelatin sizing many times in perpendicular orientation. (Total operation time for 11x15" paper 30-45secs.) 50C temperature isn't a problem as long as you use the sizing solution (with hardener) one-shot as I do; normally gelatin will loose gelling strength if rehated to above 40C several times... Using extra hot gelatin solution "once/one shot" doesn't give my any problems. (= Clean prints, no staining.)
Originally Posted by Xandros
Hope this helps,
I don't have an ultrasonic moisturizer, and bying one in a country with 300 days a year without clear sunlight ...
Anyway, yep I got your technique to rule out this parameter !
I'm using a foam brush too, gently. Also one-shot gelatin mixture. I tried mixing the hardener in the mixture, or applying it in a separate layer after the gelatin dries, it doenst seem to change the result. As for the temperature, the problem is that I didnt have that thermometer/hygrometer at the time it worked fine, so I really have no clue ... the dryest days when it didnt work were like 28░C / 35%.
Compared to your temp/humidity examples its vice versa here, high temp means less humidity.
Well, here in Istanbul a simple model (Made in PRC) will cost something like 20EUR, so it isn't a big investment.
Originally Posted by Xandros
I was trying to say that high temperature/less RH doesn't always mean that the actual moisture content in the air is less then low tempature/high RH, in other words; you have to take the temperature into account too.
Originally Posted by Xandros
Notice that the absolute moisture content of air is equal for say... 20C/70% and 30C/40%, whereas 70% and 40% figures are pretty far from each other. So, beware; RH figures can be deceiving when not paired with ambient temperature...
Last edited by Loris Medici; 09-15-2009 at 03:46 AM. Click to view previous post history.
Thanks for the great link ! I will now be able to consider the absolute humidity when printing !
As about the moisturizer, i'll consider it eventuallly even though it's a bit more expensive here.
What is your exposure source? If your doing it in the sun, I just don't think you will get consistent results. I'm sure some will disagree, but an exposure unit would eliminate exposure variables. Have you considered putting a humidifier or a dehumidifier in your darkroom to achieve a consistent environment year round?