Combine 1/2 c cornstarch; 1 c baking soda; 3/4 c water in pot. Stir over medium-low heat until like smooth, mashed potatoes. Spoon into bowl; cover with damp cloth until cool. When cool, knead well, adding cornstarch if sticky. Preheat oven to 175 F. Line baking sheet with parchment. Roll out clay to 1/4" thick on surface lightly dusted with cornstarch; cut out shapes. Place on prepared baking sheet. Use straw to poke a hole for hanging. Bake about an hour, turning over halfway through.