Fill the balloon with water . This image illustrates why you don't completely fill the balloon you should always leave some room in the neck of the balloon, then as the form dries the pressure has somewhere to go and your clay wont split.
Baking soda neutralizes the ph in the soil and is a natural weed killer. Sprinkle baking soda around all of the edges of garden areas to keep the grass and weeds from growing into flower beds. Just lightly cover the soil twice a year – spring and fall.