This is a good technique for subtle shading.
Sponge 2 or 3 chalk colors over white glossy paper and mist with rubbing
alcohol, letting colors run a bit.
Then swipe a metallic inkpad over that and mist again with alcohol, letting colors run.
Seal with fixative and stamp over it.
I used images by Paper Inspirations, CTMH & Penny Black.
*Remember that it might not look very promising before