Measure out the Brush-On 40 rubber 1A:1B by volume. Place part B of the Brush-On 40 in a mixing container first, and then combine with part A. Mix the material thoroughly. Put a small amount of the mixed material into a small cup and add So-Strong brown tint. Mix the pigment into the material. Then, add a small amount of mineral spirits to thin out the Brush-On 40 rubber and mix in thoroughly. Apply this mixture as a wash over the entire piece, taking care to coat all surfaces. Use a heat gun to accelerate the curing of the Brush-On 40.