You'll start with your favorite watercolor paper cut to the size of your card front, watercolor brushes (I used a small flat brush and a small round brush), dye reinkers, a bowl of water, a back board, and masking tape.
Start by attaching your watercolor paper to your backing board with masking tape. Tape around all four edges, creating an even border with your masking tape. This will leave a uniform white space all around the outside of your paper, which creates a tidy edge.
Choose your background colors and squeeze a few drops of each reinker color into a palette or paper plate. Using a clean brush, wet the whole surface of your paper, then begin dabbing color onto one area of the paper. The more water you add to your reinker, the more dilute the color. Add other shades and allow them to spread and bleed together. If you want them to bleed more, spray the paper lightly with water. You can remove any pooling with a paper towel. Allow the paper to dry completely and remove the tape. For the card above, I used three shades of blue and left quite a lot of the paper white.
This technique works well with bright colors as well! For this little card, I used three shades of pink and then stamped over my colored area when the paper was dry. I used a water pen to color over the ink on my heart to make it look painted on.
I experimented a lot using this technique for water as well, and came up with these cool backgrounds! Adding a sprinkle of salt when your paper is wet creates a really neat mottled effect. I also tried sprinkling water on the paper after it was dry to create some light blotches. What a messy and fun crafty afternoon!