This technique has been one that has been around for years. Again it is a simple one with supplies that are readily available.
Substrate - I used a shipping tag
Acrylic Paint or Gesso - I used white for high contrast. You can use cheap acrylic paint for this as long as it is opaque.
Stamps - Any stamp will work. I used some architectual foam stamps I have had for years.
Watercolor Medium - I used watercolor crayons
Paper towel or cloth
Heat gun or Patience
1. Stamp the acrylic paint on to the substrate. Wash your stamps immediately. Let dry or use a heat tool to dry before moving on to the next step.
3. Paint watercolor over the substrate. I smeared the watercolor crayons and then activated with water.