To make a successful cyanotype in winter, expose it around solar noon, on a clear day and in the open: an image that would take a few minutes in summer can need several tens of minutes, until the surface turns a bronzed grey-blue.
It all comes down to five rules:
- expose around solar noon, when the sun is at its highest;
- choose a clear day and place the sheet in the open, never behind a window;
- avoid the shadow of walls, which lengthens quickly in winter;
- allow several tens of minutes and judge by the bronzed grey-blue colour change, not by the clock;
- switch to a UV lamp when the sun is really lacking.
Cyanotype is seen as a summer process, and yet you can print beautiful images in the depths of winter. You simply need to know what the season takes away from the sun, and accept a slower pace. A December print is not handled like a July print, and winter is when the most common failures appear.
This page focuses on printing in weak sunlight, in winter and under a grey sky. The act of exposure itself, and the general question of timing, are covered in the page on exposing a cyanotype, and the complete guide to cyanotype places the process in its overall context.
What winter takes away from UV
A cyanotype is exposed by ultraviolet light, the invisible part of solar radiation that triggers the formation of the blue. In winter, the sun stays low on the horizon, and its rays cross the atmosphere at an angle and lose a good share of their ultraviolet content on the way.
Under a clear sky, a July noon can deliver several times more UV than a January noon. It is this gap, far more than how cold it feels, that explains why the same sheet, the same negative and the same solution need such different times from one season to the next.
Choosing the time and the day in winter
In winter, the useful window narrows around solar noon, when the sun reaches its maximum height. Early in the morning and late in the afternoon, the light remains pleasant to the eye but is already very poor in ultraviolet, and a print started too late will drag on far longer than you might think.
So wait for a clear day and start the exposure in the middle of the day. Expose the sheet facing the sky, in the open, never behind a window, because window glass blocks a significant fraction of UV. Also avoid the shadow of a wall, which lengthens quickly in winter and steals part of the useful radiation. The paper is prepared in advance, and the cyanotype kit provides ten sheets of it along with the two bottles of iron salts.
- Choose a clear day and the middle of the day.
- Expose the sheet facing the sky, in the open, with no window glass in between.
- Avoid the shadow of walls, which lengthens quickly in winter.
Set up the arrangement in the open during a sunny spell in winter, then judge the exposure by testing.
Accepting long exposures
In the depths of winter, even on a fine clear day, an image that would take a few minutes in summer can need several tens of minutes. This slowness is nothing unusual: it is the price of the season, and trying to cut it short gives pale prints that wash away in the rinse.
Only the colour of the surface is a reliable guide. The sensitised sheet turns from pale yellow-green to a bronzed grey-blue as it is exposed, and it is this colour change that tells you when to stop, whatever time the clock shows. The typical winter mistake is to reuse a time that worked in summer, then be surprised by a washed-out print.
What is still possible under a white or grey sky
An overcast sky does not rule out printing. A white, bright sky lets through a significant share of UV, and you can work under it, just more slowly. A low, leaden sky, on the other hand, makes the exposure long and uncertain, sometimes close to an hour, and a passing cloud lengthens the time without warning.
On these grey days, check the colour change more often than usual, and be prepared to stop a print that is no longer progressing rather than leaving it outside until evening.
When to switch to a UV lamp
When the sun is really lacking, in the depths of winter or in a home that gets little light, artificial UV takes over. Its intensity stays constant, which gives reproducible times from one print to the next, a real comfort when the sky will not cooperate. The principle does not change: it is still the colour change on the surface that decides.
Éric Marais — Photographer, author of two books on pinhole photography (published by Pearson) and creator of the Sténoflex. He has run introductory workshops in alternative photography, from pinhole to cyanotype, from the very beginning.