Mix cornstarch and Bi-Carb soda in a pot.
Add the water to the powder mixture. It will seem like the water sits on top, but after a little stirring it will combine into a runny mixture.
Place the pot on the stove over medium heat. Be sure to stir the mixture constantly. Once it thickens turn into a bowl. Cover with a damp paper towel and let cool.
Knead the cooled mixture until smooth. Roll out the dough to approximately 1cm thick on a flat surface. If you find the mixture to be a little sticky, add a little cornstarch. Cut out desired shape with cookie cutters. Use a drinking straw to make the hole at the top of each of the ornaments.
For Air Drying: Leave overnight but turn over before going to bed to ensure both sides dry evenly
For Baking: They will slightly brown a bit in the process. If you plan to paint the ornament, this is the best option. Preheat oven to 160C. Place ornaments on tray lined with baking paper and bake for approximately 30 minutes. Be sure to watch closely for the last 10-15 minutes to prevent over browning.