Re: Help!--chiascuro in watercolor?
Your photo is very dramatic and the lighting is what makes it so.
As you see in Uschi's painting above, It is possible to do dark in watercolor. The background of my pink iris painting (see in my signature) is also very dark and was done in several layers because I started with a lighter background that didn't work. I just kept adding deeper and deeper tones one on top of the other letting them dry completely in between and being careful not to scrumble with the brush as I put on a new layer.
I don't know if you are into air brushing but I just read Arleta Pech's book Painting Fresh Florals in Watercolor where she did one exercise using an air brush to paint a very dark background before finishing lace and flowers in the center area.
Hope you have success with your chiarascuro painting. Look forward to seeing it.