Lightfastness of chemigram colors

Collins, Study #14, 2011

We continue to think and wonder about the colors created in chemigrams, where silver halide complexes, embedded in black and white photo paper, can be induced to yield a gamut of colors from the subtlest pinks and yellows to the richest indigos and violets.  Of the many questions evoked by the chemigram procedure - and there are many - one is paramount not just to artists, the chemigramists themselves, but to collectors, dealers and museums, indeed to the whole enterprise, and that is this: how permanent are these colors?  Do they degrade over time?  Which colors change in hue and which do not?  Over what timescales do changes, if any, occur?

First, a practitioner's observation.  Chemigram colors do in fact evolve and mutate throughout the entire creation pathway, as waves of fixer, developer and byproducts besiege the emulsion.  This continues, muted, into the final wash and even to the drying.  We know it because we see it.  It seems to persist for certain tones right into the early days of the post-dry period, though we're not sure where that ends, so lowkey do the changes eventually become.  It could be related to how much silver halide still clings to the paper, or how complete the wash was.  But even discounting that, such changes are real.  That's why some chemigramists prefer to scan their work as soon as it dries, to ensure the vibrancy of the original colors is preserved.  Nothing worse than having your work disappear on you.

a QUV weathering unit

What about the longer term - years, decades - what happens then?  To help find an answer our colleagues in the laboratory at Golden Paints in New Berlin NY conducted lightfastness tests on chemigram samples we provided, using their state-of-the-art QUV apparatus.  This device exposes samples to UV radiation simulating indoor, gallery-lit conditions, but vastly compresses the timeframes: 400 hours of constant exposure in this box is the equivalent of 33 years in the real world (technical details are found on the Q-lab website).  We went for a century - a nice unit! - in three 400-hour segments, at the end of each of which the samples were withdrawn and compared to the original.  These comparisons could have been rigorously quantified in Cielab colorspace, the delta-E or amount of change could have been calculated, etc, but all we wanted was a first-look kind of result.  Here is some of what we found.

fig. 1

In figure 1 the upper right corner piece is the original; the three slices descending toward the left lower corner are pieces that received 400, 800, and 1200 hours of exposure respectively.  While difficult to see at the scale of this post, there is a slight loss of warmer reddish tones by 400 hours.  At 1200 hours there is an overall darkening, or perhaps dulling is a more accurate description, a vague muddiness.

fig. 2

In figure 2 the original is on the right, with progressive exposures increasing toward the left according to the technician's notes on the scan.  Of the many samples documented this showed by far the most dramatic changes, with the warm tones dropping out completely even at 400 hours.  The subsequent gray tone maintains its value, but darkens somewhat by 1200 hours.

It is true that the snippets sampled were not uniform or even systematic: chemigram tray time, paper type, wash time, idiosyncracies of the artists (several supplied samples) all varied considerably.  In addition, the UV spectrum used in the exposures may not be predictive of actual conditions in a gallery, where lighting can vary from fluorescent of various types to daylight.  And yet from this we feel entitled to form certain impressions - a sense of the slow degradation of the colors, some perhaps more than others, against a background of an inevitable increase in entropy.  Left unspoken is the mechanism for these changes, since chemigram colors owe nothing to either dyes or pigments but instead to the size of certain objects - polymorphic clumps of silver bromide or chloride - and the wavelengths of light reflected from them.  The Mie effect was mentioned in an earlier post, and will be revisited in the future.  Still, for now we can be cautiously optimistic in the belief that, if our chemigrams have not altogether gone bad in our trays before we hang them out to dry, they will be around in some form for quite a while, maybe a century.

2 routes to color

Collins, Aachen window #5, 2010

Collins, Problematic, 2009

Both pictures here are made without a camera but they are in fact quite different, one from the other. The upper one is a chromogenic C-print, made in total darkness in the color darkroom. As a process, it could be termed a color photogram or more accurately a color luminogram, since no objects were interposed between light source and paper. It is printed on color paper, Fuji or Kodak Endura. The colors arise from what is called the chromogenic reaction. Silver halide in the photo emulsion is reduced by developer to silver particles, while the newly oxidized developer reacts with a 'dye coupler' found in each of three layers of the photopaper. These developer-coupler reactions produce dyes of the three 'subtractive' colors of white light, namely cyan, magenta and yellow or CMY. The silver gets bleached out and the dyes give the color.

The lower picture is a different beast entirely. It is a chemigram, made in daylight on black-and-white photopaper with a chemistry of black-and-white developer and fixer. Standard chemigramic methods were used: dipping and snatching. The element of luck, absent in the other picture, here was sought out and embraced; a number of attempts at achieving this image were discarded. The creation of a color picture from b & w materials cannot help but fascinate. What's going on? How does it happen? William Jolly spent many years at UC Berkeley trying to answer this and related questions. He attributes the color to the Mie effect, by which small particles - their size must be on the order of the wavelengths in the visible spectrum - reflect back incident light on a range of wavelengths from short to long, which our brain assigns the such names as 'blue' and 'red' (the references are in his monograph). These particles of course are grains of silver, reduced by developer from the silver halide in the paper's emulsion. There are not only grains of silver, there are silver-bromide complexes, silver atoms, and other short-lived forms of silver too, all of different sizes, all buffeted by an ever-changing environment of developer and fixer and the byproducts of their interactions. It is from this stew that we get our 'color'.

Chemigramists have noticed that colors may sometimes change even in the washing or drying phase of the process, when no obvious chemical assault is occurring. That is because within the emulsion, at a very local or nano level, the action between substances may continue, although at much slower rate, before equilibrating and finally damping out altogether.

There is more to be said on this, but we'll leave it for another time. It's enough to show that there's more than one way to get color with photographic materials.