One way to add interest to your project is to experiment with different stains. Add a light-colored stain to your colored plaster to create a little depth, or use dark colors to create a dramatic texture. Just be sure not to go overboard or you may change the integrity of the plaster. Try adding one part stain to ten parts plaster, and plaster a small area of your wall to see if you like the look.
To add sheen and protection to your wall, use your trowel to apply a layer of wax as a topcoat. To keep the look from getting too waxy or slick, burnish it by rubbing the wax with the sides of the trowel. It may take a little practice before you get the technique down, so be sure to practice with your Venetian plaster and wax on throw-away boards before you start marking up your walls.
Another idea for changing the look of your Venetian plaster project is to combine a few colors of plaster. First, choose the colors for your project. Then, apply a thin layer of your base color before adding another layer with the next color. Keep adding layers until you have achieved your desired look. Adding different shades of the same color is a good way to add the appearance of additional depth to your wall. If you have a more bold look in mind, combine very different colors, such as tans, whites and purples. The contrasting colors will seem to burst through the layers, adding interest to your project.