Learners write their initials by applying different clear "magic ink" solutions to separate pieces of paper and then "develop" the inks with other clear solutions. One "magic ink" is a sodium hydroxide solution that is "developed" by phenolphthalein, an acid-base indicator. The writing can be made to "vanish" again using a hydrochloric acid solution. Another "magic ink" is a potassium thiocyanate solution that is "developed" by iron chloride, forming iron thiocyanate ions that appear red. Commercially available "Magic Pens" are also used to help learners understand how they work. For safety reasons, this activity works best as a demonstration for younger audiences.