Question

which is the substance used as invisible ink

Answer 1

Baking Soda Invisible Ink. Dip a cotton swab into a mixture of 1/4 cup (60 ml) of baking soda and 1/4 cup (60 ml) of water. Use the swab to write a message on a white piece of paper. Dip a paintbrush into some grape juice concentrate or any dark juice.