How to color plaster cast rocks

[MetroRedLine]

Before I paint or stain  plaster-cast rocks, I paint them with artist's gesso. Gesso is a medium of white paint and plaster material used by artists to "prime" a canvas before painting on it. The advantage of using gesso for model railroad scenery is to have a consistent surface material that can take paints/stains. And the added benefit is, if you mess up painting/staining your plaster mold rocks, just paint on another layer of gesso and start over again!

[robert3985]

When I started doing plaster rockwork decades ago on my Ntrak modules, I didn't want stark white showing up if I chipped any of my plaster cliffs.  So, I decided to tint the plaster, but like the OP I found that I was using too much "tint" to make it make good sense financially....and I didn't want a "tint", I wanted it colored to look like sandstone.

I decided to use powdered tempera paint...mixing it into the plaster before adding water.  Although I still had to use more than I thought I would, I found that if I used black tempera in addition to the brown, I was getting a color that was pretty close to what I wanted, and it didn't affect the setting time or hardness of the plaster as far as I could tell.

For my final finish I applied a dark base color, then dry-brushed lighter colors on my carved rocks for both the lighting effect and the texture...which worked pretty well for me. 

I didn't want my rocks to fade over time, so I used Liquitex artist's acrylics to paint them, then various washes, then a flat coating of Matte Medium before applying static grass or other ground coverings.

Photo (1) - Here's Wilhemina Pass on one of those old Ntrak modules, with rockwork done like I've described...


Photo (2) - This is the cut that defines the border between Devil's Slide and Wihemina Pass...different color rocks, same technique...


Cheerio!
Bob Gilmore

[Bob]

I would like to thank everyone for responding to this question - there is alot of good information and ideas that I will try!
Bob

[chuck geiger]

This is plaster or joint compound-covered foam. Done with several shades of Wally World craft paint, airbrushed with the same tones, and dry brushed white or linen crafty.