Find the center of your wall -- that's where you'll start making marks for the diamond pattern.
Tape the grid portion of the template to the wall with painter's tape. Use a torpedo level to make certain that the template is level on the wall, and then use the template to mark a grid on the wall in pencil. This will tell you where to place the diamond-shaped stencils before you paint. Remove the grid portion of the template.
Note: Stencil adhesive will make the templates lay flat against the wall without damaging the paint. Use painter's tape to mark off your millwork and baseboards -- anywhere you don't want paint.
Tape the second portion of the template -- a diamond-shaped stencil -- to the wall, lining up the top point of the diamond with a cross mark you made using the grid template.
Note: Templates such as the diamond pattern are available at craft stores and are made by Decorator Products.
Using a roller, paint over the diamond stencil with metallic glaze in an elephant-gray/umber/brown shade. The paint has a soft sheen.
Note: If paint fumes bother you, make sure the room you're painting is well ventilated, or wear a dust mask. Use a respirator if your paint has toxic fumes, or better yet, don't use that kind of paint, because you really don't need it.
While the glaze is still wet, daub it with a chamois patterning tool -- first dipping the tool in more glaze and dabbing off the excess on a paper towel. This will create a crinkled, almost leathery look in the diamonds.
Note: If you prefer not to purchase the patterning tool, crinkle some plastic wrap or a plastic grocery bag to create one.
Finish the wall's worth of diamonds, and then use dots of acrylic copper metallic paint to connect them to one another where their points meet. Apply the paint with a circular sponging tool. The dots will also help hide any flaws in the diamond corners. Overall, you don't want the paint to look too perfect. Instead of a uniform, wallpaper look, strive for a hand-painted effect.
If you like, use a fleur de lis stamp to imprint more patterns between the diamonds. Paint the stamp with brown paint, add a little gold around the edges and then press it firmly on the wall. This treatment also works well by itself on a wall. Make sure to space the stamps about a foot apart, to keep the pattern from looking too busy, and to save work for the painter.
After all the paint dries, if you'd like a sheen finish, seal the walls with water-based polyurethane.