Lumen / POP
Archived Posts from this Category
Archived Posts from this Category
I tried to develop a correction curve applicable to a digital negative for home-made POP, and (without being too scientific) came to use the familiar inverted s-shape again, used quite mildly though. When printing image files on transparency with an Epson Pro 3800 I realized that I’d need very high ink densities, such that Epson’s own printer driver cannot produce. A solution to the problem could be QuadTone RIP, which can separately adjust each ink’s output density. I think we should definitely check that when we get some time…
I tried a dark green hue for the UV blocking color, but even if I increased the ink density in the printer driver the output could not block enough UV light. So I thought I’d try a double negative – two identically printed transparencies registered and sandwiched together. I have noticed this being a familiar method to some serigraphy printmakers, e.g., to increase the film density. I used to think it would be hard to use in photographic images, with delicate tones and fine details, where every little bit of misalignment would show… but it was quite easy actually, and the dimensions of the two transparencies (Agfa CopyJet) really were exactly the same, so it wasn’t too hard to register and tape them together accurately.
This Photoshop correction curve was applied to the grayscale positive image, which was then inverted to negative. The image was then filled with 12R-24G-0B.
Adding silver nitrate to b&w photographic paper emulsion helps to increase its sensitivity, and the tone range will resemble more real POP. Below are some tests with different papers – the left picture shows the image after exposure, on the right the same image after the wet processing. Before the exposure all the samples were treated with silver nitrate (saltprint sensitizer: 12 % silver nitrate solution) diluted 1+2 with water.
Toning was done with two simple formulas: gold and palladium toner (see formulas below), and also Tetenal Gold Toner was used.
As we can see, the results greatly depend on the emulsion and its treatments. To get certain previsualized end results won’t be necessarily easy – accident will also play its role. On the other hand, that’s the fun of alt-printing; to achieve a wanted result will ask understanding and predicting the processes, and sometimes one has to accept anything not turning out well, and the materials seem to have their own will too…
Although not very high Dmax, this outdated Emaks paper produces a nice warm glow with palladium toning.
I’ve got to tell a bit more about my lumen printing, as it offered such fun during the summer break. I think somehow I came to realize what were the feelings of Henry Fox Talbot when succeeding in his first Photogenic Drawings.
It is a known fact that summertime weather in Finland is often cloudy and rainy (but low in snow, as they say ;-)) but nevertheless I managed to expose a number of lumen prints using sunny days. Exposure times were long though, as UV levels don’t get very high at these northern latitudes.
Almost any silver gelatin paper seems to work in lumen printing – each in its own way. In lumen printing the results can be quite diverse (as are plants themselves) depending on the paper type and the chemical processing. Moreover, the moisture extracting from plants in pressure against the paper may also create weird “auras” around the plant silhouette.
One of the problems in lumen printing is how to keep all those colors that were formed during the exposure. The image must be fixed in order to preserve it, but fixing itself, no matter how it is done, seems to lighten the image and desaturate the colors. Of course it is possible to keep the unfixed print in the dark, and only shortly view it now and then in dim light, enjoying the colors (although my guess is that changes in the unstable silver would slowly destroy the image anyway). And yeah, you can do as I have done here – scan the print before fixing, and use that scanned (and maybe somewhat enhanced) image for new prints. But it tastes a bit like cheating…
Conclusions on toning in general: Not toning (fixing only) lightens the image, but can work OK if lightening is allowed. Also, with gross overexposure and fixing the print will yield delicate “golden” tone, which can be quite attractive with certain subjects. Toning with gold will increase Dmax (maximum density) and cool down the image tone. Selenium also deepens Dmax and shifts the color slightly towards red. The sulfide toner didn’t work here at all, turning everything black like it was developer.
An example of prolonged gold toning. In spite of long exposure (on Emaks paper) image tones were quite weak after the exposure. With a long (7-8 min.) gold toning the tones got deeper, and remarkably colder at the same time. There are also yellowish areas in this image, due to plant extracts reacting with the silver emulsion.
Another problem related to a long exposure is the plant tending to dry and stick to the paper during the exposure. The heat in bright sunshine has an effect on this too, so sometimes, after the exposure, it may be hard to separate the plant from the paper without tearing the paper.
To avoid these harms I tried to find a way to increase the paper’s speed. One possibility could be to dissolve the silver of an unexposed paper by fixer and then wash it away. The remaining gelatin base could then be hand sensitized with silver nitrate, using the salted paper or vandyke method.
Instead I decided to try the silver nitrate method straight; I had silver nitrate sensitizer left over from salted paper tests done a couple of years ago. It was the standard saltprint sensitizer (12 g silver nitrate + 100 ml water), which I further diluted 1+2 with tap water.
When I finally learned how to do this extra sensitizing properly (I used a foam brush to coat a dampened photo paper with silver nitrate in dim roomlight) the increase in sensitivity indeed was noticeable. For example, the 7-8 hours exposures on Emaks shortened to half to two hours. In addition, adding silver led up to dramatic increase in density.
Here’s another sample of gold toning, which makes the dark tones bluish and yields a nice split tone.
By coating an ordinary silver gelatin paper with silver nitrate I can increase the paper speed and get better Dmax. But I wonder if there’s a way to preserve the produced colors so that they wouldn’t fade in the fixer? I tried sort of “desensitization” by using very diluted chemicals with very short treatment times, fixer and toner in turn, one after the other several times, with washing in between. I was hoping the short treating times would not make great changes, so I could slowly “harden” the print to stand the chemical treatments without changing too much.
This is the best I could do with preserving the colors. The print was treated several times in diluted palladium toner and fixer (Hypam 1+20) for a few seconds at a time, with water rinsing in between.
I’ve got heaps of outdated black&white photo papers from 1980s, some of them quite legendary brands like Agfa Brovira, Record-Rapid and Portriga-Rapid, and also Emaks and Varycon by Fotokemika. So I thought, instead of throwing them away, I might try lumen printing; a great way to use old and partly fogged papers.
Lumen prints are essentially plant photograms, printed with sunlight. Printing resembles normal contact printing, but the “negative” is a plant, sandwiched between a glass plate and a photo paper, and the exposed paper is not supposed to be developed but will print out a visible image during the exposure (like “real” printing-out papers do).
Of course, these papers were originally not made for this purpose, and to form an image without developer you need to expose for a very long time even in the brightest sunshine. The more UV light you get the faster are the exposure times. Different manufacturers’ papers can be very different in sensitivity to UV light. In these tests exposures ranged from half an hour to 7-8 hours.
After the exposure the print is washed in water shortly, and then fixed. Normal modern photographic fixers lighten the print considerably. Even when used standard sodium thiosulfate fixer for POP the lightening effect may be strong. In that case it is advisable to tone the print in gold or platinum/palladium toner before fixing. Normal final print wash follows after the fixer.
Essentially fresh plants (not dried) should be used in lumen printing. Juices extracting from plants have an important part in reacting with photographic emulsions, forming special colors and effects.
There are methods for estimating the strength of UV radiation on each day, from which (and with a little experience with the light sensitive materials) one can judge if the exposure is going to be long, or very long.
Centennial from Chicago Albumen Works is genuine printing-out-paper. It doesn’t need to be developed, and inherently produces good maximum blacks with much shorter exposures than my home-made pop papers. This is an untoned, fixed Centennial print.
To get back to lumen printing, we tried again some over-age papers by exposing them to the sunlight. At the time of the tests the UV index was not yet very high in Finnish spring, but we exposed these prints out in the sun for several hours.
It seems that Dmax of these papers (used this way) is quite low, and you can not increase it by exposing more; with overexposure you just get your highlights murky and lower contrast overall. The print looks pretty nice right after the exposure, but will bleach considerably in subsequent wash and fixer (but I guess the fixer is necessary to ensure the printÂ´s longevity). Maybe we should try toning with gold or platinum, before the fixer, and see if it would prevent bleaching.
As it turns out, the paper prints the whole Stouffer 21-step wedge, all the way from step 1 to 21!
To make another quick “Lumen” test for UV-blocking properties of an inkjet transparency, printed with an Epson 3800, we exposed a sheet of over-age Emaks paper through the printed film (as in the previous test on 28 Feb) in our UV-box for several hours during two days. The result is below (the color shift is quite interesting):
There really is only one possible patch producing the lightest tone on this paper, corresponding to this particular “neon green” on the transparency: 0, 255, 170.
How will laser printers perform at the UV-blocking test then. Not very well, we can tell you:
None of the color densities that the printer (Canon iRC3200) could output on it’s general use OHP transparency can’t hold UV-light, it will penetrate through all the hues almost equally well.
Now we are just waiting for the sunny spring days to come soon (with light rich in UV), so we can load our printing frames and leave them outside to expose some Lumen for us … ðŸ˜‰