Combine baking soda and cornstarch in a saucepan and mix well.

Add cold water and stir until the mixture is smooth.

Bring the mixture to a boil and cook for 1 minute, until it reaches the consistency of mashed potatoes.

Spoon the mixture onto a plate and cover with a damp cloth to cool.

Knead the cooled dough.

Roll the dough out on wax paper.

Cut out designs using cookie cutters or shape them by hand.

Poke a small hole in the top of each ornament with a straw.

Let the ornaments dry until hard, about 1-2 days.

Paint the ornaments with tempera or watercolors.

Let the paint dry.

Coat the ornaments with clear shellac.