Making rock castings for your model railroad

 The
 Superior Products and Woodland Scenics molds are typical commercial products. Scene Tints are water-based paints that can be used before casting.

It's fairly easy to make your own rock molds. The hardest part may be locating a rock, or rocks, with enough surface detail to be interesting at a scale size; coal also works very well.

Once found, clean the rock surface of dirt and paint on a layer of liquid latex, let dry, and repeat. After you've made several layers, it's a good idea to place a layer of gauze over the mold and attach it with another layer of latex. One or two more latex layers will result in a mold that will withstand many castings.

For those who don't care to make their own, many excellent rock molds are sold in hobby shops.

Rocks come in many varieties and the mold you choose, whether commercial or home-made, should represent an appropriate type for your area or scene. I wanted clearly stratified rock to represent lannon stone, a common building stone quarried in nearby Lannon, Wis.

You can use the same mold several times by turning the casting upside down, breaking it in pieces, or just putting it next to different castings. For a quarry, even greater repetition is okay because the mechanical process of removing the stone creates a more regular surface than found in nature.

 These two molds were applied to the slope while the plaster was still wet. The molds weren't removed until the plaster had thoroughly set.

Though Hydrocal is often recommended, U. S. Gypsum no. 1 casting plaster of paris is perfectly satisfactory and costs much less. If you're doing a large layout, it's worth your time to find a source for large quantities of plaster, typically 50- or 100-pound bags. Check the Yellow Pages under plaster.

Always mix plaster by adding plaster to the water. The ratio should be about two parts plaster to one part water by volume. This produces a pancake-batter consistency. Water-based paints or dry pigments can be added to the water to give a base color to the casting.

Spray the mold with water mixed with a drop of detergent. This will help the plaster fill the mold and act as a release agent after it has set.

Pour the plaster into the molds, poking it into crevices with a finger or stick, and let it begin to set. Molds with a lot of relief may require support to hold them level. Wadded newspaper or almost any scrap material will usually suffice.

If you want to place the mold on the scene while still wet, you need to time it so the plaster is no longer runny but has not yet begun to crystallize. Before placing the mold, lightly wet your base plaster so that it doesn't suck the water from the casting.