Palette knife (or other dull blade)
Wood or linoleum carving tool
Black acrylic paint
Brown or gray spray paint
After deciding what the sign will say, layout the design using paper and a pencil. Make sure that the letters are large and easy to read.
Cut the foam into the approximate size of your paper template using a blade. Please do this work in a well-ventilated area, since the foam will make lots of nasty dust that's easy to breathe in and hard to clean up.
Lay the paper template over the foam square and firmly press the letters into the face.
Once a rough outline of the words can be seen, dig out each letter with the carving tool, making a little trough about Â¼" to ½" (0.64 to 1.27 cm) deep, being careful not to punch all the way through the foam.
Once the words have the desired appearance, take a dry brush and remove as much loose dust from the grooves as possible.
Using a dull blade, scrape away at the edges and corners of the sign. Remember this stone has been hanging for a long time and has become worn. Knock off the clean right angles of the foam, smooth them out, wear them down. A dull file can even be used for some interesting texture. Keep in mind that the foam will flake and shred, giving way to interesting planes to work with.
Once the shape is perfect, use black acrylic paint and a dry brush to daub into the bottom of the grooves to make them more visible. Set the signs up across the room and have a look at them. Are the letters visible? Can you clearly understand the words? Cut and paint as needed to increase visibility.
When the words and the shape are right, its time to add the texture. Don't forget that some spray paint can dissolve Styrofoam, so keep a light touch on the spray can. Working outside or in a well-ventilated area, spray the stones in your background color in short bursts. Keep the can moving constantly and the application light.
Once it is coated evenly, allow the sign to dry for about an hour.
Then, go back over the sign (with a different color, if desired) to add age spots, divots, and shading.
Allow to dry overnight.
The next morning, give the back of the sign a quick coat of paint and let dry.
© Helene of Troy's tutorial was taken with permission.