Prepare your stencil. Either download one from the Internet and print it, or draw one by hand. Use your Exacto blade and cutting mat to carefully cut out the diamond pattern. You can also purchase small diamond stencils at hobby shops.
Place your picture flat on newspapers that are laid on a flat surface. Position your stencil on top of the picture.
Dip your brush in the selected paint. Lightly brush the paint across the cutout diamond, beginning on the outside of the diamond and brushing towards the center. (Starting in the center and moving outwards will cause the paint to clump up under the stencil.)
Peel up the stencil once the paint is applied to your satisfaction. Roll it off by lifting one side first. Be careful not to smear the paint.
Let the paint dry until hardened. This may take 15 to 20 minutes.
Clean your brush with the water; then dry it with the paper towel. Lay your paint brush flat or hang it to dry with the tip down so the bristles won't get ruined.