A 1/2 gallon carton of Lightweight Hydrocal® will yield approximately 14 medium-sized rocks.
The actual number of rock castings will depend on which Rock Mold is used and how full it is filled. For example, Rock Mold Strata or Classic and a 1/2 gallon of Lightweight Hydrocal will yield 8-10 full-pour rocks.
Hydrocal® is a U.S. Gypsum registered trademark.
We typically suggest Yellow Ocher, Burnt Umber and Black for generic rock coloring, however different geographic locations have rocks of different color so choose the pigments that best represent the area you are modeling.
The Leopard Spot technique is our favorite method for coloring rocks. It is a simple technique that yields realistic results. Start with the suggested dilution ratios. If darker colors are desired, add additional pigment to washes.
-Dilute 2 different secondary colors, 1-part pigment to 16-parts water. Color suggestions: Yellow Ocher and Burnt Umber.
-Dilute a third pigment for a dominate color, 1-part pigment to 32-parts water. Color suggestion: Black.
Start with the lightest secondary rock color. Using a foam brush, dab first color randomly over 1/3 of rock. Rinse brush. Dab the next secondary color randomly over a different 1/3 of rock. Rinse brush. Leave approximately 1/3 of the rock white.
Brush and dab the dominate Black Wash over the entire rock face. The Black Wash pulls the colors together. When dry, seal rock colors with Scenic Cement (S191) and let dry. Then, brush on a less diluted Black Wash (1:16) to accentuate rock detail. Spray again with Scenic Cement to seal.
Rock Molds are made of a non-latex polymer.
Yes, the black wash can be lightened, as long as it has not been sealed already with Scenic Cement. Flood-spray the casting with hot salt water (1 tsp in 6 fluid oz of hot water). Wait one minute, and spray again if needed. Dab with paper towels to remove the liquid. The base colors will remain on the rock, but the coloring will be much lighter.
If you would like to start over completely, paint the casting with White Earth Colors Liquid Pigment. Dilute the White Pigment 1:1 with water.
When satisfied with the coloring on your casting, spray with Scenic Cement to seal the colors and let dry.