"I need a heck of lot more of these ..."

Easy Duplication

Nyuk, nyuk, nothing is ever easy. But wouldn't it be nice to have a big pile of these little skulls for you terrain.

Simple

The easiest stuff to use is Hydrocal or plaster of paris. Simply soften up some plasterscene (modeling clay) and push your piece into it. Fill it up with hydrocal and let it dry.

Mold Materials

Not going to lie. This is the stuff the masters use. It works great. Costs lots. And they have a section on mold work. http://www.smooth-on.com/

Here is a vid using real old plastic from them in a plastercine mold.

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Preparation

Collect lego blocks.

Tips and Tricks

Pour plastics from high in a steady, very thin, stream. This helps elongate the airbubbles and forces most out.

Vacumn de-air

Would be nice to have one.

Problems!

Expense.