Found on a web forum I occasionally read.
The poster gives a tutorial, including photos of his ongoing process, on
how to use silicone molding compounds and plaster of Paris to create molds
to cast items out of resins, in this particular case the joystick to a
Tron video game. While I hope that its application to doing things like
creating pyramids should be obvious :-) it's a darn cool tutorial if you
like to make stuff with your hands. And, generally, a darn cool web site
if, besides that, you also like arcade video games.
It was also featured on the MAKE blog:
(If anyone's out there thinking "Well, duh! It should be obvious!" it
wasn't obvious to me.)