I was recently inspired by bi-color cyanotypes I saw online, and wanted to take a crack at the process myself. I started simply with solid colors rather than printing with negatives, as the testing process would probably be very long for the latter. I first wanted to see what this process is capable of.
Since I'm sure everyone is familiar with how cyanotypes are made, I won't describe the process in detail. The yellow layer in bi-color cyanotypes come from bleaching a blue cyanotype with sodium carbonate (washing soda). I use 1 tsp sodium carbonate to 1 L hot water, and bleach the cyanotype to completion. My first tests were to determine how much exposure was needed to achieve a satisfactorily yellow layer.
I expose my cyanotypes using a DIY exposure box, lined with UV LED strips. The UV intensity in this box is rather low, so my exposure times tend to be longer. However, I can achieve much greater consistency using my exposure box than relying on sunlight.
From left to right, the exposure times are 30m, 60m, and 90m. Not a huge difference between the three prints at this stage.
The same prints, but fully bleached with sodium carbonate. Despite the initial prints having very similar values of blue, here it's apparent that the overall exposure during the blue step makes a big difference in the yellow value.
On each bleached print I coated another cyanotype layer and exposed all three for 30 minutes. I reduced this exposure time for later prints, but it's still easy to see that the darkest yellow combines best with the blue layer to make green. The fact that the blue and green aren't too different in value makes the prints feel a little flat.
Here is a later print that I'm happy with, with the blue layer receiving less exposure than the prints above. The exposure may have been on the light side, but the color separation is much cleaner:
I have more experiments I'd like to attempt with this technique, so stay tuned for more soon.
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