Do exposure times affect print quality?

Rolleiflexible · Jun 21, 2022

I just built a UV LED light box, using inexpensive (but well-built) self-contained fixtures from Onforu (Amazon). They dramatically shorten my exposure times from eight minutes to 30 seconds. An unexpected bonus: The prints I am pulling with them also seem to have darker blacks, clearer highlights, and more apparent detail.

I am wondering: Do longer exposure times cause some sort of veiling effect? Or is something else going on here?

(If anyone wants to explore the lights, Google "CTB96UV" -- that should bring up the Amazon listing. The lights come in pairs, each measuring about 5.5x15 inches -- butt the two together and you have a 11x15 UV LED light source for $69. (Add two more for a 15x22 light source for $138.) Each unit is rated at 96 watts. Build quality is good -- anodized aluminum casings and brackets, and a glass cover. I made a stand from a 2x2-foot sheet of ply, supported by 9-inch legs, and mounted the lights on their brackets underneath.)

Sanders McNew
www.flickr.com/sandersnyc
www.instagram.com/sandersnyc

MattKing · Jun 21, 2022

I don't know the answer to your question, but I do know that the arrangement of a lighting array can affect the apparent "sharpness" of a contact print.

Ethan Brossard · Jun 21, 2022

is this with pt/pd printing? I don’t have any experience with the process (too expensive for me at the moment) but I’ve heard that shorter exposure times are generally better

Rolleiflexible · Jun 21, 2022

Ethan Brossard said:
is this with pt/pd printing? I don’t have any experience with the process (too expensive for me at the moment) but I’ve heard that shorter exposure times are generally better

Kallitypes. I am toning with platinum but I'm not sure how the toner would matter.

Ethan Brossard · Jun 21, 2022

Rolleiflexible said:
Kallitypes. I am toning with platinum but I'm not sure how the toner would matter.

Kallitype science is similar to pt/pd, so it might be similar in that regard too

TheFlyingCamera · Jun 21, 2022

Longer exposure times, especially with lights that produce a significant amount of heat, will have a negative effect on print quality because so many of these alt processes are humidity dependent, and those really long exposure times allow the coated solution to begin to dry out, which impacts contrast and sensitivity. It becomes a vicious cycle - with longer exposure times, you lose contrast and sensitivity, one of the cures for which is longer exposure, which further decreases contrast and sensitivity. And so on. So yes, having powerful, fast LED lights makes your exposure cycle much shorter which benefits your overall print quality.

Rolleiflexible · Jun 21, 2022

TheFlyingCamera said:
Longer exposure times, especially with lights that produce a significant amount of heat, will have a negative effect on print quality because so many of these alt processes are humidity dependent, and those really long exposure times allow the coated solution to begin to dry out, which impacts contrast and sensitivity. It becomes a vicious cycle - with longer exposure times, you lose contrast and sensitivity, one of the cures for which is longer exposure, which further decreases contrast and sensitivity. And so on. So yes, having powerful, fast LED lights makes your exposure cycle much shorter which benefits your overall print quality.

Scott, interesting. Temperature can’t account for it — my old lamp was also a UV LED fixture, hanging almost two feet above the paper (to minimize falloff). But you might be onto something with humidity. I imagine a long exposure gives those UV buggers time to meander around and cause mischief. I wish I had stayed awake in physics.

nmp · Jun 21, 2022

Heat is a particular problem with silver nitrate as it will accelerate its reduction to silver without any UV (dark reaction) in the paper (buffered paper more so than non-buffered ones.) But as you said, perhaps that is not operative here as in the first case you have pretty open design and good bit of distance from the UV source (unless there is some IR coming off of the metal enclosure and reflector.) Still the 8 minutes are probably not that long to really heat up the paper - I used to do 30 minute exposure for my POPs and it used take the temperature of the glass on the frame to some 140 F, forcing me to add an exhaust fan to my exposure box made of BLB spirals.

Incidentally, the source to paper distance in your new system is nearly 1/4 that in the earlier one (2 feet vs 5 inches) - which would be about 1/16 reduction in the light intensity (square of the distance.). That could explain your exposure time reduction by 1/16, if the power at the source were to be comparable.

Anyway, enjoy the unexpected bonus...

:Niranjan.

Ian Leake · Jul 16, 2022

The highest Dmax for iron-based UV processes will be when the sensitiser is damp enough to almost stick to the negative and is on the paper’s surface (as opposed to having been absorbed too far into the paper fibres).

I think what’s happening is that with the long exposure (+heat) the sensitiser is drying out, thus reducing Dmax.

It may also be that the sensitiser is sinking further into the paper fibres but I think this is less likely.

Vaughn · Jul 16, 2022

There are a lot of factors in play.

Do Kallitypes create a printed-out image during exposures (seems like most alt processes do....pt/pd and cyanotypes -- even carbon but you can't see it)?

1) Longer exposures allow the printed-out image to have a greater effect than with quick exposures. Since the image forms stronger with more exposure, the printed-out image acts as a printing mask to hold back the highlights, allowing for richer blacks and good separation in the mid-tones.

2) Flourescent tubes create a very diffuse light -- known to produce less sharpness and less contrast than light sources closer to a point light source. So improvements on those two factors are often seen switching to LEDs (if everything else remains the same).

3) Actual wavelength of UV (and high-end blue) can make a difference -- and this differs with each process and how one uses them. Especially with single-wavelength LEDs, they should be choosen to match the process. Wavelength will affect sensitivity, depth of penetration, etc.

And of course, if one changes paper or many of the other many variables, those will change printing speed, etc.

esearing · Sep 1, 2022

Just increase the distance between print and light to reduce your times. Using the UV strip at about 6 inches from the print, I get about 6-10 minutes for iron based "Lobotype" prints , salt 30-45 minutes.

KYsailor · Feb 13, 2023

Rolleiflexible said:
I just built a UV LED light box, using inexpensive (but well-built) self-contained fixtures from Onforu (Amazon). They dramatically shorten my exposure times from eight minutes to 30 seconds. An unexpected bonus: The prints I am pulling with them also seem to have darker blacks, clearer highlights, and more apparent detail.

I am wondering: Do longer exposure times cause some sort of veiling effect? Or is something else going on here?

(If anyone wants to explore the lights, Google "CTB96UV" -- that should bring up the Amazon listing. The lights come in pairs, each measuring about 5.5x15 inches -- butt the two together and you have a 11x15 UV LED light source for $69. (Add two more for a 15x22 light source for $138.) Each unit is rated at 96 watts. Build quality is good -- anodized aluminum casings and brackets, and a glass cover. I made a stand from a 2x2-foot sheet of ply, supported by 9-inch legs, and mounted the lights on their brackets underneath.)

Sanders McNew
www.flickr.com/sandersnyc
www.instagram.com/sandersnyc

Just wanted to thank you for this recommendation, I am just starting in Alt processes and the winter weather is so bad here in Kentucky , the sun is unreliable. I was about to buy a bunch of raw 3 watt UV LED chips, mount and wire them in a box.... but this is a much better approach. They have actually come down in price - I was able to get the "2-Pack" for $55. If I may ask what is the distance from the glass surface to you contact frame. You mentioned putting 9" legs on your backer plate, however the units stand off from your backer plate by some distance. Just curious. Since I am not planning on doing any prints larger than 11x14 these two units should work very well. BTW really enjoyed your site, I am an ex film/darkroom guy in my high school days, however I have converted to digital and haven't looked back - although I look fondly at my old film cameras occasionally. Again thanks for the recommendation.

David Najewicz
Prospect, KY

David Najewicz Photography

www.tumblr.com

Rolleiflexible · Feb 13, 2023

David, I am not on the PHOTRIO Welcome Wagon, but I'll welcome you here all the same. There is a lot of cumulative knowledge archived here, and a lot of current users who have experience to share. Stick around.

I am glad you found the suggestion useful. I tried a couple of other solutions, and like you was preparing to spend a lot of time and money building an exposure box from scratch, when I found these lights. Honestly, they are a thousand dollars cheaper than the usual solutions (NuArcs and such), and faster and more reliable too. Using a vacuum frame with a clear vinyl top (which removes the glass, which absorbs some UV light) my exposures are 23 seconds for kallitypes.

You are correct: I hung the lights, using the included brackets, from the bottom of a sheet of plywood that stands on 9-inch legs that I cut from a poplar closet hanging rod. That leaves plenty of room for the print frame. I'm attaching a photo so you can see how I've set them up.

Feel free to ask questions, here or in a private message, if I can offer any additional help. What process are you expecting to print with?

KYsailor · Feb 15, 2023

Sanders - Thank you so much for answering my question, and attaching a photo of your set-up, that makes it very clear...I have been "trolling" the alt photo stuff here on Photrio and have found it very useful as well. I did some cyanotype's last summer and got some OK results ( however interrupted by a house project and am just getting back to it). While the cyanotypes were OK and I learned all the curve/digital negative stuff, I am not that enamored of the blue color.

I have seen some pt/pd prints in museums and was impressed with the tonality and overall look, and I was down in Raleigh and saw some Van Dykes at a gallery that were very impressive as well ( the photography not so much). I am going to start first with some Van Dykes and I have a set of kallitype chemicals as well. I am going to try it after I practice a bit on the Van Dyke process. Ultimately, I plan on doing some toning with the Kallitypes to get then to approach the pt/pd look. I have been gifted a fair amount of rag paper from a retired watercolorist ( my mother in law) who had quite a stash, so I will see how that works and give that a try, at least initially. Bergger COT 320 seems to be the paper of choice for these processes so I will probably end up with some of that as well.

Thanks again for your reply and helpful comments - you live in a beautiful part of the world. I had a photographer friend ( he was a film/darkroom guy) who lived in Asheville for several years and captured some beautiful images from the surrounding area. Unfortunately he left the area....

Regards

Dave Najewicz

David Najewicz Photography

davidnajewiczphotography.tumblr.com

Sirius Glass · Feb 15, 2023

KYsailor said:
Sanders - Thank you so much for answering my question, and attaching a photo of your set-up, that makes it very clear...I have been "trolling" the alt photo stuff here on Photrio and have found it very useful as well. I did some cyanotype's last summer and got some OK results ( however interrupted by a house project and am just getting back to it). While the cyanotypes were OK and I learned all the curve/digital negative stuff, I am not that enamored of the blue color.

I have seen some pt/pd prints in museums and was impressed with the tonality and overall look, and I was down in Raleigh and saw some Van Dykes at a gallery that were very impressive as well ( the photography not so much). I am going to start first with some Van Dykes and I have a set of kallitype chemicals as well. I am going to try it after I practice a bit on the Van Dyke process. Ultimately, I plan on doing some toning with the Kallitypes to get then to approach the pt/pd look. I have been gifted a fair amount of rag paper from a retired watercolorist ( my mother in law) who had quite a stash, so I will see how that works and give that a try, at least initially. Bergger COT 320 seems to be the paper of choice for these processes so I will probably end up with some of that as well.

Thanks again for your reply and helpful comments - you live in a beautiful part of the world. I had a photographer friend ( he was a film/darkroom guy) who lived in Asheville for several years and captured some beautiful images from the surrounding area. Unfortunately he left the area....

Regards

Dave Najewicz

David Najewicz Photography

All Images © David Najewicz 2010-2022, all rights reserved

davidnajewiczphotography.tumblr.com

Welcome to ~~APUG~~ Photrio!!

Rolleiflexible · Feb 15, 2023

Dave, happy to oblige. Several thoughts:

Before you give up on cyanotypes because of all the blue, you might want to investigate the vast range of toning possibilities that cyanotypes offer. Toning with various tannins can give beautiful tones. You can do a deep dive into cyanotypes, using new formulas pioneered by people like Mike Ware and Sam Wang, and using all sorts of split toning techniques that produce gorgeous results. Routledge published a book on cyanotype toning by Annette Golaz in 2021, that is a worthwhile source book on the subject. It's not my medium, but I respect the process and its possibilities.

My medium, at least for now, has been platinum-toned kallitypes. It is, for me, the sweet spot in the alt processes. If you are considering this route, make sure you read Sandy King's writings, which give a reliable guide to getting started. If you run into problems, ping me -- I'll be glad to help if I can. And while I am not a Facebook user, there is an Alternate Photography group there with over 45,000 members worldwide, and I have found it a good source of information and inspiration.

One big issue as you move away from cyanotypes is paper. Your rag paper stash will work fine for cyanotypes, but probably not for kallitypes or straight pt/pd prints, which are not tolerant to a lot of buffering agents found in most papers. The Bergger COT is one reliable standard, along with Arches Platine and Rives BFK (Irving Penn's paper of choice) and Hahnemühle Platinum Rag. My favorite, FWIW, is Revere Platinum, from Legion Paper (which also sources Arches Platine and Rives BFK). Legion sources it from an Italian mill to Legion's spec, formulated precisely for these processes. Revere Platinum looks and performs much like Hahnemühle Platinum Rag, but is a lot less expensive.

Sorry to run on at such length. As M. Twain said, I would have written a shorter note if only I had the time.

KYsailor · Feb 17, 2023

Sanders, thank you so much for your recommendations regarding these processes, sorry to reply via this thread, I would DM but I have too few posting for that feature to be enabled. I tried a bit of toning with tea on some of my cyanotypes (attached), however I was using some kind of cellulose paper or some of my inkjet paper and it stained rather badly and I did not like the results. I have a copy of the Christopher James book on Alt process and it has many suggestions regarding toning of cyanotypes, perhaps with better paper/toning medium I can get better results.

I may circle back to cyanotype, however your recommendations on paper are very helpful - the alt photo sites seem to have a lot of somewhat contradictory recommendations on papers. Interesting comment regarding Irving Penn. Pre-COVID I spent a summer in Pittsburgh and attended an excellent exhibition of his work at the Frick Museum (like all the robber barons, Frick left a few traces in the 'burgh before moving on). I was really impressed with Penn's work, I was aware of his work mostly as a fashion/commercial photographer, however his personal work was also excellent. I do remember his prints were beautiful.

Well thanks again, I hope to get my UV box assembled this weekend and perhaps I will get organized enough to attempt a few Van Dykes next week....also enjoyed the Twain the quote - fully understand I have that problem myself.

Dave Najewicz

David Najewicz Photography

davidnajewiczphotography.tumblr.com

cliveh · Feb 17, 2023

As all my exposures for alternative process applications happens dry, I would say no.

Perry Way · Mar 1, 2023

This is a great thread. I have a muse whispering in my ear saying give this a go for all the alt processes I wanted to explore years ago but never did. Gum Bichromate, Salt Printing, etc..

Not able to start on this right now but I want to see any other posts that happen so thus my comment.

Vaughn · Mar 1, 2023

Vaughn said:
There are a lot of factors in play.

Do Kallitypes create a printed-out image during exposures (seems like most alt processes do....pt/pd and cyanotypes -- even carbon but you can't see it)?

1) Longer exposures allow the printed-out image to have a greater effect than with quick exposures. Since the image forms stronger with more exposure, the printed-out image acts as a printing mask to hold back the highlights, allowing for richer blacks and good separation in the mid-tones.

...

This is embarrassing. #1 should have read: ... Since the printed-out image is stronger in areas that get more exposure (in the shadow/black areas), it masks (holds back) those darker values. But it does seem to make for smooth transitions between tonalities and allows for easier handling of those shadow areas.

Do exposure times affect print quality?

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