One of my fave mediums to use on a card is light modeling paste because
1. It dries super fast!
2. It can be manipulated to hold peaks for cool textures.
3. It sits nicely on watercolour paper without causing significant warp.
On this card, I applied a thin layer of light modeling paste with The Crafter's Workshop stencil. Then I added some colorants before applying gesso [black and white] to really define the textures.
Playing along with CAS(E) this sketch!