There are lots of magazine articles and books about how to make rock castings. This article just presents one idea I tried, and it worked for my particular situation.There are lots of magazine articles and books about how to make rock castings. This article just presents one idea I tried, and it worked for my particular situation. I needed to create some thin rock castings for a particular section of one of my N-scale layouts where the track was a bit too close to the edge of a cliff. The commercial rubber molds I had purchased in the past work well, but most of them are rather deep. To use them to make thin rock castings means pouring in a thin layer of plaster. Removing the castings from the mold can break them quite easily because they are so fragile. I am sure I have read this somewhere before, and so it may not be a new idea, but what I came up with was to take a piece of aluminum foil, crumple it up, and use that as the mold.
Don't crumple it up too tight.
I then unwrapped the ball of foil. This takes a bit of patience as the foil can tear very easily.
After mixing up the plaster (in this case "Plaster of Paris"), I poured it over the foil and let it dry overnight.
When the plaster was dry, the next step was to remove the casting from the foil. Because of the deep ridges in the foil, some of the foil was hard to remove. Some of the pieces were still a bit too thick for my layout, so I tried another approach. I crumbled up another piece of aluminum foil, and then spread it out on the workbench. I smoothed it out a lot more.
As an experiment I also added a bit of acrylic Burnt Umber to the plaster as I was mixing it. It colored the whole batch nicely, however, I did notice that the plaster started to set really fast. I quickly poured it on my new mold and spread it out.
Within about 30 minutes I could remove the plaster casting from the foil. This time the foil came off easily and it didn't tear, so I could use it again.
Here is another close-up view of the rock castings covering the entire cliff. I also used the famous alcohol-and-india-ink mixture to stain the castings. This really helps to define the rock edges. I then used some white acrylic paint and used the "dry-brushing" technique to highlight some of the edges. Some additional color stains were used to highlight some other rocks. When I took this photo I was in the process of filling the gaps between the rocks with ground foam, as well as spreading grasses on top of the cliff.
This photo shows some of the first batch castings installed on the rock cliff that was really close to the track.