Contact printing – Solar intensity evaluations

I am still plagued by being a science-nerd which is kinda of cool when my sense of curiosity overlaps my artistic instincts. Something that I have yet to read about regarding alternative photography processes involving contact printing using solar power to create the artwork (e.g. cyanotypes) is how to evaluate one’s solar light intensity? Here in Southern California we are blessed with lots and lots of clear blue sky, but sometimes we have a cloudy day. Dense cloud cover could bring solar printing to a stop, but then there are those days with the thin white clouds, aka Cirrus, overhead and the resulting light appears pretty intense, but how intense is it really? How then does one adjust for the slight decrease in the sun’s intensity?

This question arose last week when we had the Cirrus clouds overhead and the sunlight appeared really intense enough to print a cyanotype, but was it really adequate? Then it dawned on me; I have just the equipment to determine the solar intensity, even if I did not have a mathematical formula of how to compensate for change in sunlight intensity. Thus, I pulled out my Pentax 1 degree spot light meter I use for my analog photography and my little (petite) hiking gray-card, shown above with my contact fame during a cyanotype exposure.

The spot light meter was reading the gray value at 13-1/2 on the Cirrus cloud day, although I did not try to print my cyanotype then. That would have been a crap shoot as I was unsure what a clear blue-sky sunny day reading would be and how much of a difference the Cirrus clouds was making. Okay, I do believe the I had recalled that on sunny days and in direct sun, this gray card would read about 14-3/4. This light meter does not have a digital readout, with two hash marks between each of the prime values in the display, so the exact value is relatively close.

The full sunlight blue sky value was confirmed the following day; at noon the gray card was reading 14-3/4 and my resulting cyanotype print appeared spot-on (yes, a very terrible pun). You may note that I stated that this gray card reading is what I read at ‘noon’. Knowing that the sun’s intensity does change during the day, I did a blue-sky full sun test this morning at 9am and the gray card value was 13-1/2. Hmmmm, no cyanotype printing yet. At 10am, the gray card value was 14-1/2, close but not the 14-3/4 reading, which I did finally obtain at 11am. And when I made my first of two cyanotype prints today, which appear great at this point before the 24 hour curing.

If somebody wants to pay for my time and materials, I could over the span of a couple of days, determine the gray-card readings and using a test negative, try to create an exposure curve. Which could result in having a gray card reading that was not ‘prefect’ and know how to compensate for the additional time for exposure to obtain a desired print. Nevertheless, I don’t know how to compensate for when the sunlight is not perfect, but now I have a good idea of being able to determine if I should print at all. Now all of print notes will include the 1 degree spot meter reading of my gray card and I suspect over time I will have a pretty good idea of how to compensate for less than ideal solar printing conditions. Or I could just give it up and purchase a UV printing stand for the studio, but what fun would that be?

Meanwhile, the enjoyment of alternative photography and investigating cyanotype printing continues on.

Cheers & make every day an Earth Day



 The Flow of Light Brushes the Shadow, an artist book from Singular Images Press, Fall 2022 release, $60.00 (CA sales tax for those residing in the USA) plus shipping expenses. Message me or singularimagespress@gmail for shipping details and PayPal invoice.

Note: The Artist Special Edition (book + extra print) is Sold Out

Book workshop:

Southeast Center for Photography (SEC4P): Creative PhotoBook workshop, (Sold Out) a virtual event on Zoom; February 25, 26 & March 4 & 5th 2023; from 10am – 1 pm, EST (3 hour session each day, with a week between the weekend sessions to work your book-dummy). 


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