RE: slightly OT: tea toning cyanotypes

Yes,
 
I have used tea a lot (pure "powdered" tea worked better than pure tannin and is MUCH cheaper) with cyanotypes. Do it of course as the last step as it can't be washed afterwards, and will affect any subsequent layers of cyanotype that you apply.
It changes the colour to anything from brownish to purple tones, depending on the strength of the solution. I use it selectively in parts of the image to get a greater range of colours from my cyanotypes.
Occasionally the tea toning causes the image to lose a little definition in detailed areas. I assume tea is archival, but haven't researched it.
 
 
Jane.