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Watching paint dry: the dry-down effect visualized

On page 44 of “The Photographer’s Master Printing Course” (ISBN 1-85732-407-2, 1995), Tim Rudman gives his readers some important advice that experienced printers often give to novices; to quote him:

“Whether exposing for test strips or work prints, always base exposure calculations on dry prints. This is because prints, especially on fibre-based paper, darken as they dry – the so-called ‘dry down’ effect.”

This is a piece of advice many inexperienced printers, including myself, more often than not choose to casually ignore. As Tim explains, the effect is considered to be most pronounced in fibre-based papers, which I currently do not use and do not have on stock. I do, however, use resin coated (RC) papers a lot and I have noticed some perceived changes of my prints when they dry over night. On this Steve Anchell writes in his book “The Variable Contrast Printing Manual” (ISBN 0-240-80259-4, 1996):

“Finally, early RC papers suffered from a dry-down effect known as ‘veiling’ or ‘hazing.’ The blacks, which appeared luminous and shiny when wet, became ‘veiled’ with an unpleasant matte appearance when dry. This was especially apparent with glossy surfaces. The problem was more severe when the paper was air-dried. Some paper manufacturers have addressed this problem with varying degree of success.”

Unfortunately, he does not discuss the effect for fibre-based papers.  Both books are roughly 20 years old, and it is unclear to me if manufacturers have improved their papers in the meantime. I also do not know why the effect should be more pronounced when a print is air-dried. If you know, drop me a line, I am curious to learn more about this. To find out whether this dry down effect is indeed significant and noticeable I went about and devised a test to visualize this effect and be able to quantify it to some extent. Do you only need to convince yourself or only want to see if these authors were right? Skip to the results!

Test outline

For this test we will be literally watching a print dry and compare the results with a completely dried print. The sample image is a photograph of a grey chart that consists of 26 grey patches ranging in brightness from 0 – 100% in 4% increments, and two opposing continuous gradients.

Homemade grey chart for dry-down test.
Figure 1: Homemade grey chart for dry-down test.

I got this chart printed by Profotonet to make sure I had a calibrated reproduction of the patches. I chose to get this printed on Ilford Galerie Panchromatic paper, as this is their recommended choice for black-and-white prints. When you print this at home using an uncalibrated printer, the shades at the ends of the spectra can start to blend and become indistinguishable for visual inspection. Under even lighting conditions (achieved as explained in the Methods Section) the sample is photographed on Kodak Tri-X 400 at 1/125 s and f/8.0. The film was developed in Kodak D76 at 22 C for 8 1/2 minutes, and consecutively spent 1 min in 1:19 Ilfostop acidic stop bath and 4 minutes in Ilford Rapid Fixer at film strength (1:4). The film was then washed for 10 minutes under running water and rinsed in Kodak Photoflo 200 at 1:200 dilution for 1 minute before air-drying over night.

Using variable contrast (VC) papers real grades can no longer be distinguished. The realized gradations are a combination of the enlarger, paper, developer and filter. For this test the used gradation is therefore, in my opinion, arbitrary. I normally start at gradation filter 2 and will use this as a representative case for this test as well. For the print I use Ilford Multigrade IV RC Deluxe paper with a pearl finish. This is developed in Ilford Multigrade developer at 1:9 ratio at 24 C for 2 minutes, followed by a 30 second Ilfostop stop bath at 1:19 dilution and a 4 minute fixing bath in Ilford Rapid Fixer at paper strength (1:9). All chemicals are freshly mixed for this session. After fixing the print remains in a water bath and is moved outside for washing after a few prints have been processed. I do not have running water in my darkroom, so this is the way it has to be for now.

Figure 2: The setup used to reproduce the print.
Figure 2: The setup used to reproduce the print.

The print was reproduced as explained in the Methods Section using the setup of Figure 2. The print was hung above a tray to dry and to avoid any liquid from dripping on the table. A weight was suspended from the print to keep it hanging straight. The photos were taken at four moments: 1) with the paper in the water, 2) just out of the water, 3) mid way air-dry (at 5 minute intervals) and at last 4) fully dried. The photos can be seen below in the results section.

 

Results

The results of the test surprised me. As I was expecting to see at least some darkening of the print, I was proven wrong. As can be seen in Figure 3 there is no apparent darkening of the entire print. As the water film flows down in the first few minutes contrast is lowered and the blacks appear slightly less deep. The corners of the print curl slightly during drying, introducing an apparant local darkening which are caused by local changes of the illumination angle. As soon as the initial water film has disappeared, there is no perceivable dry down anymore. These results are consistent with the experiences of others with contemporary RC papers.

Watching a print dry.
Figure 3: Watching a print dry.

In Figure 4 the wet and dry print (after 60 minutes of drying) are compared side by side. There are some minor differences, which are highlighted in red. The differences are minute but perceivable. As no drydown is apparant when the water film has disappeared it is adviseable to wipe of the initial film using an appropriate paper squeegee.

Figure 4: A side by side comparison between a completely wet RC print on the left and the same print after a 60 minute period of air drying.
Figure 4: A side by side comparison between a completely wet RC print on the left and the same print after a 60 minute period of air drying. Three small differences are indicated: (1) & (3) the blacks appear deeper in the wet print; (2) overal contrast is lower when dried.

Discussion and Conclusions

From the test with RC paper can be concluded that the drydown in contemporary versions of Ilford Multigrade RC Deluxe paper the drydown is minute. However, the water film that sits on the paper when it is just pulled from the bath makes the blacks appear deeper and overall contrast to be higher. It is advisable to use the appropriate paper squeegee tongs to remove the excess water before judging a test print, but waiting for it to dry completely seems unneccesary. Chris Wallers’ suggestion of applying a 5% correction in exposure time appears to be a good starting point for RC papers when judging them when wet. As multiple people do report a more pronounced drydown in fiber based papers, I will repeat the experiment later. Stay tuned for that update!

To get an expert opinion on the matter I have reached out to Harman Ilford and Adox. Although Ilford does not have any factual evidence to support their claims, they did answer my questions based on their experiences and general beliefs. Their answers reflect the most likely reasons of several people within the Ilford company and their aggregates experiences. To start off they support the notion that RC papers show none or very little drydown, and they have not observed it in their RC papers historically either. It is their belief that glossy surfaces suffer more from apparent drydown than matte surfaces, because of differential gloss and densities showing darker or lighter depending on the surface finish. Glossy surfaces seem to enable more variation than matte products when it comes to this. To the question why air-drying should supposedly result in a more severe drydown, Ilford technicians belief that drydown is dependent on the temperature and cooling rate. This is linked to wet paper swelling up as the fibre base structure opens up. Dependent on how quickly or smoothly that structure swell goes back to normal seems to impact on how much darker prints dry down. Their experimental findings, however, show no significant differences between drying techniques (but it has been a long time since they carried out a controlled test for this).

I also contacted Adox about  the same issue, and they replied by first stating that at the current market size and volumes research and development is at an all time low. It is sad, but to be expected I am afraid. Paper drydown is at least no longer on their list of research topics and they advise using the same methods as found elsewhere: do not judge prints when they are wet or apply a correction to the exposure time. When it comes to Adox, they consider this the simplest “problem” in this industry today.

This experiment started out as a mere curiosity and the drydown effect was something I needed to verify for myself. Further discussions with Ilford has led me to conclude that I took the most ideal conditions when it comes to drydown: I chose for a RC paper with a non-glossy surface. To see drydown I should try a fiber-based glossy paper and repeat my tests. Nonetheless, I am still interested in the underlying science of drying paper. If you can explain the differences between RC and fiber based papers, know why the effect should be more pronounced when the paper is air dried, or where to find answers to these questions, please let me know!

Published in In the Lab