9 parts cornstarch
4 parts water
See the Science Chapter for more instructions, hints, tips, and ideas.
This is fun and amazing stuff! After it is made, it will change back and forth between acting like a liquid and a solid. It's named after the Deep Space 9 character who could change shapes and forms.
Fluids like water are Newtonian fluids - we are familiar with how they act. The changeling is an example of a non-Newtonian fluid which means that it behaves strangely. When you move it fast like hitting it, rolling it into a ball, or squishing your fingers quickly through it, it behaves like a solid. If you hold it still or move your fingers slowly, it behaves like a liquid. Quicksand is another example of a non-Newtonian fluid.
When you grab some (which is not an easy feat in itself), place it in the palm of your hand and roll it into a ball. It will act like a ball of clay and the outside of the ball will be dry. When you stop rolling it, it will immediately start turning into a puddle. You will notice that it is shiny and liquidy.
I made it using 1/2 teaspoon as my units (so 2 teaspoons of water and 4 1/2 teaspoons of corn starch). That made enough to play with and fill a film canister about half way. The easiest way to get it into the film canister is to let it puddle in your hand and then scrape it into the bottle.
Of course, I made a neckerchief slide out of it!
It does tend to grow mold after a couple days, so play with it quickly and throw it away when it goes bad.