Particle jamming is amazing. Take a balloon, fill it with some granular media like uncooked rice or beans and suck the air out with a vacuum. The balloon stiffens and holds its shape. The stiffness of the bladder is easy to manipulate and quickly changes from a completely floppy state to something as hard as a rock. The higher the vacuum, the stiffer the jamming bladder becomes. Of course, the granular media that you put inside the bladder also affects its performance. Fill a balloon with jelly and it’ll remain relatively malleable even with a high pressure vacuum. On the other hand, if it’s filled with glass marbles, you’ll won’t be able to shift its shape whatsoever once a high vacuum is pulled. That’s the magic of particle jamming.
With that little piece of magic, we developed a process to create custom molds for thin shell casting using various granular media. We worked with two primary variables. The granular media and the shape of the bladder. The thin shell casts take on the form of the shaped bladder as well as the granular media, crystallizing the intricate texture created by the relatively coarse grain. Choice of granular media affects the stiffness of the bladder, the stiffness of the cast, and the texture of the cast. Glass marbles casts have a stiff structure with a hexagonal pattern of craters while rice creates a fragile structure with an irregular speckled texture.