Not entirely 100% successful but we do have yellow, blue, and green…ish blue. I have to change how I create the channel negatives. What I did for this was just taking the Cyan and Yellow channels of a CMYK image, but that doesn’t really work all that well.
So this image is not the best example of what is possible, but if I posted only success stories it would look like I know what I’m doing, and we can’t have that. 🙂
The process is pretty simple – the yellow layer goes first, it’s a normal cyanotype just bleached with household soda. Then washing and letting it dry and then another layer of cyanotype solution, and that forms the blue channel. A red channel is also possible, but I have to acquire the needed stuff for toning it red first (madder root works well apparently). I tried black tea but that just made a deep brown, which isn’t all that useful for this.
There’s a more detailed explanation of the process over here but I only followed 10% of the instructions and it sort of worked anyway.