Okay kiddies, listen closely.This is the only hard and true fact of making foam tombstones that I know of: aerosol paint will melt bare foam. Always base paint the tombstone first with a latex paint. Make sure it's totally covered, even a pinhole in the basecoat will let in the propellant and your foam will disintegrate. From experience I can tell you this usually occurs in the worst spot--the epitaph. I have lost entire phrases. Go over all engraving carefully and touch up any bare spots. Base painting your stone in a similar shade to the granite spray will save money as you can use less to cover the stone, however contrasting colours can make for interesting effects. As always, do not be afraid to experiment

A quick side tip:
Hammer a nail into the drip trough of your paint can. Excess paint will drain back into the can and the lid won't stick so badly.

There are so many ways to finish your tombstone, I will only cover the few I use myself. There are probably a hundred more ways I do not even know about. Please don't take my word for anything, experiment! Your finished tombstone should reflect your style and the style of your haunt. There is no one perfect way. You may wish to combine several of the following techniques.

If you like the look of marble, Krylon has a wonderful effect paint called Webbing Spray. It is basically a paint that sprays  like fine Silly String. Try base painting your stone in gloss black. Stand a few feet away from the dry stone and let the strings of paint float over it. Use a light touch. You can find Webbing Spray at most craft stores.

Bob Poniatowski sent me a tip for an inexpensive way to finish base painted tombstones. Carefully pry the plug from a can of black or grey spraypaint. The larger opening allows more of the paint to spray through, creating a nice speckled effect. Use this technique directly on your base painted stone, or combine it with other techniques.

Another nifty tip posted to the list by Jawbone: set up your carved and base painted stone outside. Spray the tombstone with your garden hose making sure to completely wet it. Spraypaint a small section of the wet tombstone with black or grey spray paint and hose it off immediately. Do not use a hard spray, just shower it, letting the paint run down in rivulets. The spraypaint will stick to some areas more readily than others and run down, creating a dark and creepy aged effect. Experiment, you'll see what I mean. It's only scary the first time. Try combining this method with the wet warping technique.

If you have a little extra cash to spare, Plasti-Kote makes a product called Fleck Stone, a faux granite finish effect spray. This spraypaint comes out in different subtly coloured "specks". It comes in different colours, mostly greys, beige, brown, some blue or green. It is a little on the expensive side, $7 - $10 a can, but if you plan to keep your stones for a long time, I find it is well worth the extra money invested.
After your basepaint is completely dry, simply spray on a light coat of Granite Spray. If you need a heavier cover use a second coat after the first is dry, as opposed to spraying heavily once. Once the granite spray is dry, seal it with a clear topcoat. Plasti-Kote makes an exterior clear top coat designed specifically for the granite spray. It's fairly inexpensive, tough and one can will seal quite a few tombstones.

I love using the garden hose painting technique over this.
Most old tombstones do not have recessed areas of designs and epitaphs painted of course, but it is at this time we have to balance the idea of realism with the theatrical. You want your designs to be seen, your epitaphs to be readable, even under the most subdued night lighting. My favorite way to do this is to fill in these areas with a watered down black or grey acrylic paint, just dark enough to look like natural dirt inside lettering and recessed areas. An eyedropper, a small brush and some paper towels (for the occasional "oops") is really all you need. After dry, another quick coat of a sealer is a good idea.

Look at the difference between a water painted stone without accent and with:

Recently I began experimenting with lighter colours on my stones and by combining techniques. I base paint in flat white and cover with one of the lighter shades of granite spray--Alabaster, Soapstone and Sante Fe Sand are my latest favorites. I then accent the designs and lettering with an appropriately darker shade of acrylic paint and seal. After the topcoat sealer is completely dry I use the garden hose method, using several shades of light to medium grey spraypaint. The total effect is spectacular.

After everything is done, you can also age your stones with a light misting of a darker spraypaint. Stand a few steps away and let the paint drift over the stones lightly and build up as you wish. To draw your eye to epitaphs, try misting the darker spraypaint around the edges of the stone, leaving the epitaph area somewhat lighter. This should give somewhat of a "spotlight" appearance. To accent add on pieces, such as a skull or an urn, try spraying from below the piece to create a weathered look or from above the piece for that creepy "flashlight-under-the-chin-lets-tell-ghost stories" look. Oooh, spooky. On green granite tombstones, I like to mist with a metallic copper spraypaint.

There are no hard and fast rules when it comes to creating a beautiful faux cemetery (other than that spraypaint/bare foam thing). It's all a matter of your own personal style. Mistakes? No such thing. I tell everyone that I do not believe there is such a thing as a "ruined tombstone".A pinhole in the basepaint, spraypaint ate your epitaph? Route out the area, cut the lettering from thin foam and glue in. Kitty sharpened his claws on the stone? Use the edge of your sanding block to create long gashes or cracks in that area. Spouse backed over the foam with the car and left tire marks? I can think of half a dozen humorous epitaphs to put on that piece of foam! Tombstone completely broken in half? Paint the broken edges appropriately and lay the stone in your cemetery with a tree limb across it.

Keep in mind that these are all just suggestions. Some things I learned in theatre tech years ago, there may be new and better ways to do things. Some I made up as I went along, some I fell upon by accident, some I swiped from others. I am no genius, I have just made alot of fake tombstones. The point is, it is just foam. Anything can be fixed, reworked or made better. So use your imagination, remember to base paint thoroughly and as I always say BE SURE TO SEND PICTURES!!