The following is a typical example of our process for creating a stone. We used beaded styrofoam for this particular stone which typically can be purchased at a home improvement center.
We took a pattern from a pumpkin carving kit and printed it on card stock. The areas were cut out as if we were carving a pumpkin, making a stencil of the image. Since aerosol spray paint eats away at styrofoam, we are going to use it to our advantage. We taped the stencil to the styrofoam and a heavy coat of flat black spray paint was applied. Please be careful to only spray on the stencil. You want the spray paint to only dissolve the cutouts of the stencil.
This is the stone once the pattern has been removed. Since the paint was applied heavily, there were some drippings on the stone, but no problem, it added to the aging process.
A close up of the picture. You can adjust the depth of the cutout by how much spray paint you apply.
The stone is carved! We used a variety of tools that we found at the Hot Wire Foam Factory. The engraving tool was used for the cracks and some of the lettering. We used the sculpting tool for the larger letters by bending the wire to the width of the lettering. It was very simple to cut out a large letter with one pass. We also bent a wire to a round shape for rounding off the stones edges.
The first step in the painting process is to paint all the indents (cracks and lettering) using a small paint brush and flat black latex paint. This adds depth to your indents.
We then "seal" the stone with a latex point that is close to the final color. Once sealed, we will be able to use aerosol paint without harming the styrofoam.
While the stone is still wet, we use a commercial granite spray paint to apply to the stone. It seems to adhere better when the undercoat is still wet and we use less spray paint. There are also a variety of methods to simulate granite, but we haven't experimented with any of those... yet. Spraying at an angle prevents a lot of buildup in the indents. You want some of the black to still show.
The first step in the aging process is taking a flat black spray paint and spraying about two feet above the stone. The older the look you want for the stone, the more you should apply. You also want to avoid windy days. Be careful not to get too close to the stone or you'll get black splotches. We also spray a little green at the bottom of the stone to simulate moss, or mold.
Finally, we take a flat cream or white and dry brush on highlights. Dry brushing is a technique where you dip a paint brush into the paint, wipe off as much as you can on a paper towel and then paint with the brush. The end result is a light application of the paint. We highlight the cracks to simulate a long period of water run off. We also highlight the bottom edges of the letters causing them to stand out more. Be creative, but also remember a little goes a long way. We created one stone which looked like a flock of birds attacked it! Good Luck with your stones!