Dealing with Dry Down

The dreaded ‘dry down’ is an effect which causes the tonality of a print to change significantly as it dries, both with regard to luminosity (darkening) and colour (shift toward more neutral). It affects fibre based papers much more than resin coated ones, and is particularly acute with matte emulsions.

The basic fix is a shorter exposure than what would one come up with based on the wet print, and a longer spell in the toner. But before getting into how to arrive at the correct exposure, a couple of side notes.

Preliminary Notes

A common theory is that dry down is caused by the paper shrinking as it dries, but I doubt this is the case. While shrinking an image does make it look more contrasty (you can easily test this by scaling a digital image on a computer screen), the size change during drying is totally out of proportion to the luminosity change, which can be a 1/4 of an f-stop. More so, most of the dark down happens in the very final stages of the drying, at which point the majority of the shrinking has already happened.

If shrinking of the paper base was indeed the primary cause, we would necessarily see similar scale of luminosity changes as the paper shrinks and expands with changes to temperature and humidity in its environment, which we do not (if you have ever made the mistake of taping an FB print to a mount all around its four sides, you will be painfully aware how big the environmental size change can be, yet it has no bearing on luminosity whatsoever).

But we do see noticeable changes if we superficially wet the emulsion without soaking the paper base, so I suspect dark down has more to do with the properties of the baryta clay used on FB papers than the paper base. But that’s a speculation on my part, and TBH, I don’t care that much.

Some printers also speak of ‘dry up’, the print getting lighter, as well as ’dry down’; it is then said that matte FB paper suffers ‘dry down’ in the highlights and ‘dry up’ in the shadows. My experience doesn’t bear this out at all, and if this distinction was real, then the primary characteristic of the print impacted by drying would be contrast, so it could not be fixed by reducing exposure (which everyone agrees it is).

However, with some papers the hue change that comes with drying can be perceived as brightening of the shade (e.g., this is quite pronounced with papers that have a greenish tinge), but this is a qualitatively different problem than dry down, one addressed easily enough by toning.

The Common Technique

The most common approach to dealing with dry down is to do some tests on the paper to work out the necessary exposure compensation, and then apply it to the final print. There are even (expensive) enlarger timers that can store the relative adjustment value and apply it for convenience.

I don’t find this approach satisfactory, it neither matches my own experience of how dry down manifests itself, nor is it well suited to working in a small darkroom.

My basic observations about dry down are:

• Dry down is most significant at the two ends of the grey scale, bright highlights and shadows,

• Of the two the loss of highlights (sparkle) is more acutely perceived, but the impact on the shadows (loss of texture and detail) is quantitatively much greater,

• The impact of dry down is not merely an objective property of the paper, but a subjective quality of the image, with images that rely on lot of shadow detail being much more visually affected by it,

• Most of the tonal change happens in the very final stages of the drying, so the effect can only be judged on a print that is totally dry.

The subjective element of how dry down is perceived means no single exposure compensation will be optimal in every case. There is also the fact that while tests can be made, there will always be variations based on paper and chemical batches, but working with matte FB paper requires the exposure to be dialled very precisely to get the print right; a 1/12th of an f-stop can make a huge difference on the shadow end of the scale.

Further more, the fact that the quantitative change at the high and low ends of the tonal scale is significantly different means it cannot be fixed by a single exposure adjustment: compensating solely for the highlights will not yield best possible results in the shadows (and in any case, the most effective way to deal with the loss of sparkle is bleaching). But compensating for the shadows might require contrast adjustment not to blow out the highlights too much, which the standard exposure compensation method doesn’t facilitate.

And not least, there are the practicalities. The traditional approach requires that all working judgments are made on wet prints. This might make sense if you are working in a big commercial lab, with large washing tank, where all the prints can float for the duration of the session, but it is wholly impractical if you are working in a small darkroom.

It also means that if you are reprinting an older print, you need to re-soak the reference print.

Different Approach

Let’s just look at the problem a fresh: the challenges caused by dark down arise because judgements are being made on wet prints — it would seem the most obvious solution is to stop doing that. And while drying FB prints takes long time, the necessary judgments can be made on small test strips, so if we can come up with a way of fast drying test strips, we can bypass the bulk of the dry down problem altogether.

Which is why a heat gun has become an important tool in my darkroom.

Drying a test strip with a heat gun is very simple: I clip it into a stainless steel clothes peg, which has a bit of an insulated wire attached to it to hold it by (as the peg gets very hot). Holding it by the wire I place it against my Belfast sink, and run the heat gun up and down it. The moisture condensates on the sink, and I move the strip along the sink and also turn the strip around to dry from both sides.

Some care needs to be taken not to burn the strip, but it takes under a minute to dry it completely.

A well selected strip makes it possible to work out both the required exposure and contrast accurately most of the time. I then make a test print (or two with minimal tweaks, if I got some doubts about the first print), and leave those to dry on a rack completely before making the final assessment.

Generally speaking, the test print gets neither bleached nor toned; the bleaching will unblock the highlights on the actual prints, but the effect is easy to visualise looking on the test print. The toning will increase the overall contrast a bit, but I find I rarely need to make adjustments for it (it will depend on how much the print is toned).

However, selenium toning is also impacted by dry down (in terms of hue), with the print shifting back toward more neutral colour. So it is necessary to tone to a slightly richer tone than seen in the toner bath, but with little practice this can be judged well enough during the toning without a reference print.