Apply a base coat of latex paint with a roller to prepare your marble paint surface. Use a 1/4-inch-nap roller pad to achieve a relatively smooth coat and use the basic background color you want for your marble. As you roll on the paint, dip the tip of a 2- or 3-inch paintbrush into each of your faux finish colors and fling spatters of the faux finish colors onto the surface. Then roll through them with your latex color. This will give you a blended-color base coat, mimicking true marble, which does not have any solid-color layers. Allow the base coat to fully dry.
Dip the tip of a stiff-bristle brush, such as a kitchen scrub brush, into one of your faux finish colors, then blot the brush on a piece of paper so there is only a little paint left on it. With the bristles aiming downward and one end of the brush pointed at your faux marble surface, place the edge of a palette knife in front of the bristles and draw it back toward you so the flat of the blade makes the bristles flick a spray of paint onto your surface. Spatter your full faux finish surface in this manner, using both faux finish colors and making sure the pattern is random--heavier in some spots and lighter in others.
Snip the tip off a long, stiff feather, using scissors to cut the spine but not the fronds, so you have a "V" shaped tip. Dip this into your faux finish color that has the highest contrast with your base coat and use the feather to draw veins on your marble surface. Hold the feather sideways so the ends of the V trace each other to form a single line, then occasionally twist the feather so the line splits into two. It may be helpful to use a photo of marble or a piece of real marble to give you an idea of how the veins look. You will be doing multiple layers, so don't put too many veins in each layer. Allow this layer to dry completely.
Pour clear acrylic glaze into three containers and add a bit of your faux finish colors to two of them, leaving the third one clear. For each faux finish color, add just a little at a time, stirring well, until you can spread your glaze on the side of the container and see a slight amount of color while the container itself is still visible through the glaze.
Sponge these glazes on, using mostly one color glaze, followed by the second color and blending them both with the clear glaze. Press or dab the sponge onto the surface, rather than wiping it on. The texture of the sponge is a part of the marble faux finish.
Continue alternating layers of spatter and veining with layers of glaze. If your veins show through too clearly, add more color to your glaze. Reduce the amount of veining with each layer. Most marble finishes take five to seven layers to look right. If your look moves too far away from your base color due to heavy veining, spatter or glazing, mix some of your base color with the clear glaze and sponge it on as you would the faux finish colors. Allow each layer to dry completely before adding the next.
Sponge another layer of clear glaze over the top once you are satisfied with the look.