Use a painting sponge or a bunched up rag and a slightly darker shade of your basecoat to create mottling or the blotchy pattern that is a hallmark of real marble. Dab and smear the surface of the countertop with the paint-covered sponge. Be creative in your strokes; try not to use the same pattern across the counter. This would make the surface too uniform and less realistic. Let this coat dry. Add the look of veins using assorted sizes of artist’s brushes to add to the realistic marble appearance. Use different paint colors as well, such as white, gray or black to get the effect you’re looking for. Move the brush with uneven, diagonal strokes making “Y” or “K” shapes, taking care to not make them too straight or too uniform (you can smudge your lines a bit, if they don’t look realistic enough). Consider strengthening your veins by reinforcing lighter-colored ones with darker colors and vice versa. Let these dry.
Use a real piece of marble or granite, or a photograph, as a guide to make a realistic appearance with mottling, veins and other characteristics of stone.
Practice mottling and veining on a piece of cardboard before attempting the technique on your countertop.
You can take a faux-marble artisan’s approach and use feathers to make your veins.
To achieve a granite look, choose three accent colors appropriate for the base color you’ve chosen. Remember you want the colors to be natural-looking, for example colors that often appear in granite, so do your research on how granite actually looks. Pour a small amount of the first color into a paint tray and then use a painting sponge to create splotches of one of these colors onto your base coat across the entire surface of the countertop. As with faux marble, dab and smear paint on with the sponge. Let the paint dry. Repeat this process for the second color. Make sure that you let each color show through. Pour the third accent color into a paint tray and add a little bit of water. This time you’ll dip a small- to medium-sized paintbrush into the paint/water glaze you made and then lightly shake the brush over the countertop to splatter the surface with tiny specks of paint. For more precise detail, you can run your fingers (wear rubber gloves) across the ends of the bristles to flick or mist the paint into tiny specks across the surface. Let the paint dry. Some granite patterns include veining, like marble. If you want this effect, just follow the same procedure as you would for marble, as described above.
Be careful when splattering paint to create a granite effect that you don’t cover up the other accent colors. Splatter sparingly and only add more when needed.
Practice splashing or flicking paint on a piece of cardboard before you start using the technique on the actual countertop so you get a feel for how to do it correctly.
Wear safety glasses when splashing or flicking paint from your brush for the faux-granite appearance.