How?
To create my cyanotype prints, I begin by uploading one of my original digital photographs into Adobe Photoshop. There, I remove all color, leaving only black and white. Taking the black and white values, I invert them to create a negative of the digital image. After formatting for size, I print each negative onto transparency film. [Below (1), a completed digital negative.]
(1) A newly printed original digital negative.
To start the cyanotype process, I hand paint cyanotype mixture (ferric ammonium citrate and potassium ferricyanide) onto my selected paper type and allow the mixture to dry. I then overlay a digital negative on top of the dried cyanotype and hold the negative in place with a glass pane. Exposing this in ultraviolet light, my cyanotype print forms. Immediately following exposure, I wash the print in water. [Below (2), I wash a freshly exposed cyanotype and finish the print by adding hydrogen peroxide to enhance the deep blue hues.] Left to dry (or I use a hairdryer), my cyanotype prints are finalized and ready to be framed.
(2) A freshly washed cyanotype, finished with hydrogen peroxide to enhance the deep blue hues.
Why?
It's fun.
P.S. Just kidding. I am drawn to value and shape in art. Usually, this turns monochromatic for me. Next time you're scrolling through your phone while sitting on the john, try turning a photo on your camera roll to black and white and then zoom in or play with the crop. It won't disappoint.
P.S.S. Did you know a women using cyanotype prints was the first to publish a photographic book? Google Anna Atkins.