 At this stage, I like to add dirt texture to the terrain. For this, I use a plaster tempera paint mix since I can completely control the color of the dirt. This plaster dirt is based on the zip texturing technique that was popularized by Lynn Westcott in the 1960s. Real dirt is generally too dark, but I can control the color completely with my dirt powder mixes. To make the dirt powder, I mix about 8 to 10 parts plaster of Paris to color. Here's some typical formulas I use. For gray dirt, 2 parts black, 1 part brown, 24 parts plaster. For tan dirt, 1 part black, 1 part brown, 1 part yellow, and 24 parts plaster. Red dirt, 1 part black, 3 parts brown, 1 part yellow, 24 parts plaster. To protect the backdrop from getting covered with dirt powder, tape some sheets of paper to it along the horizon. I remove most of the sticky from the tape so it won't pull the paint off later when I remove the paper. I mist the area first with water, then use a tea strainer to apply the dirt powder. I apply just a light coat. Once I'm done spreading the dirt powder, I spray another mist of water to dampen it. You don't want to apply it too thick, or the plaster won't absorb the moisture completely through, and the powder will remain loose. If you need a thicker layer of dirt, then apply several thin layers to get the thickness you want. I apply this dirt powder to the entire area and make sure it sets up well with no loose spots. To apply the dirt powder on vertical surfaces, fold a piece of paper and dust a little dirt powder into the fold. Now, wet the surface with a sprayer, hold the paper up to the area and blow. Repeat as necessary to get the surface covered with the dirt powder to the degree that you want. Once I'm done with the scenery to this point, I remove the paper protecting the backdrop, pull up the masking tape, and vacuum up any loose debris. So there we have it, our basic scenery terrain. Now we're ready to move on to doing the scenery details.