The usual way to tone cyanotypes involves a bleach, watching the print like a hawk while it slowly disappears into magenta then yellow, pull it out of the bleach, wash it, and then cross your fingers that you did not take it too far. The print is then put into whatever a tannin-rich liquid. A goat is then sacrificed to make sure that the tonal range returns from its pale state.
(Artwork in video by https://www.instagram.com/yvonnewartiainen/)
By accident, I found a much safer way to tone prints that seem to work with some toners. I have tried this for chestnut and acorn. The process is easy. Simply soak the print in the tannin-rich liquid first, and then put it in bleach second.
The print does not fade when it goes into the bleach. Instead, it slowly changes to the desired tone, and you can pull it out when you are happy with the result.