Question about mixing henna with other herbs

[cmnt831]

So, I know henna is permanent, but it seems that other herbs, dyes, etc. like cassia, buxus and indigo and paprika either aren't permanent or can be temperamental as far as staying power. If I was to choose to mix henna with something like cassia, for example, would the cassia eventually fade and leave the redder tones of henna behind, thus necessitating another full application (rather than a roots only application) of the original mix of henna and cassia to bring it back closer to the original tones? Or am I off base on this? Would the henna just keep getting darker as more layers are applied despite adding cassia? Or could you do a mix with more cassia than henna with each successive application and keep the henna tones in check that way? (Ex. 50/50 Cas/Hen 1st app.; 70/30 C/H 2nd app.; 90/10 C/H 3rd app.)

I'm hoping to do my own testing on hairballs at home, of course, but wondered if anyone here has any experience with it already.

I've been trying to search for this answer myself, but haven't been having any luck. Maybe I just think too much or am getting bogged down in details.... :lol: Thanks! :flower:

ETA: I think I've got the answers I need now. :)