Making a cyanometer to measure sky moisture through color
I love simple field arts tools for my kit, and a recent discovery (thanks to our Skyscapito Appreciation Society comprising weather and cloud nerds), is the cyanometer. Encompassing the word for the primary color blue, “cyan,” it is a simple manual tool for measuring a meteorological phenomenon.
The cyanometer was developed by Swiss meteorologist and geologist Horace-Bénédict de Saussure in 1789 to measure the blueness of the sky and thus its moisture (and particle) content. The paler the sky, the more water vapor is present in the atmosphere; clouds are dense with moisture and the blue visible spectrum we see in the sky is scattered in all directions by the water in these pockets of condensing moisture, making them appear white. The darker values mean there is less water vapor so more of the pure blue spectrum is visible (and it’s most blue straight overhead). This scattering of light is known as Mie scattering (or Raleigh scattering, depending on the atomic particle size).
Saussure’s original cyanometer (left, which resides at the Bibliothèque de Genève, Switzerland) had 53 values of Prussian blue. It was held up and compared to the color of the sky to select a value. Alexander von Humboldt used the cyanometer on his voyages and explorations in the Americas in the late 1700s.
Another use for this tool would be to use it to match blue values from the sky to your notebook for getting the hues just right for different parts of a sky.
You can make your own cyanometer, choosing a blue shade that best approximates your typical regional sky. A compass and ruler are helpful to create the circle and partitions. I made mine to fit into a pocket in my journal, so it is about 5.5 inches wide.
Create a disk using a pencil and compass. Use a ruler to divide into 16 spaces. Note that I added a third circle to demarcate a space for the scale, which starts at 0 for white.
To reserve a white line between values I added wax lines using waxed paper scribed with a pencil.
I chose cobalt blue, mixing a very pale wash for the first layer, covering 1–15.
First wash is very pale. Once dry, add another wash starting with #2 and ending with #15. Continue drying, adding layers (3–15, 4–15, etc.), until halfway, when the values are saturated.
At that point, begin adding a wash of dark blue such as indanthrone, eventually ending with pure dark. I used a white colored pencil to enhance the numbers and lines in the dark values.
Cyanometer in use, showing a #6 value sky, which tracks well with the 42% humidity that day.
Bethan Burton, of Journaling with Nature, posted a short video of her process for making a cyanometer, which is a little different from mine. Both work really well.
You can also use this wheel to match colors in the sky to a painting in your notebook!
The next meet-up of the Skyscapito Appreciation Society is Friday, August 13 at 3 pm Pacific time, and we will be practicing making cyanometers. Details and registration link is on the Skyscapito page (link above) or in the Events and Workshops area of this website.
