After putting in the crack try hitting it with a heat gun. It will open the crack and give it a more natural edge.

 

You have to wiggle the knife back and forth, and pop out little bits of foam as you go. Terra and SK Austin have videos on YouTube showing the process. A heat gun or acetone can help with the final eroded look.

 

Thank you.

 

Just a Swiss Army knife. Twist the blade as you go. Have some sections that are done with the blade turned flat so it's not actually cutting. Just hack and slash, go in different directions, have it branch off into two sections, have different areas be different widths, different depths, on and on. Experiment on a scrap piece of foam and see what happens. Have fun!

 

I do mine with a woodburning tool with an exacto tip. Gotta get a little wiggly with it. No straight lines. I'll come back with a regular exacto blade and pick at some areas to widen/damage them more too.

 

Nice work!

 

If you're using pink or blue foam, you can use Acetone on a fine paint brush. If you're using white foam, it will eat straight through it.

 

The Swiss Army Knife method describe above is what I use. Learned that from someone here on this forum or another one very similar.

 

The cracks in the stone from Nightfisher are as good as it gets. Going to try and duplicate those on my next one. Very nice work.

 

Small wire brush on the white foam