Samuel Rubin
This book presents a comprehensive guide to the many forms of invisible inks used in espionage, conjuring, and communicating secret messages. Includes recipes and a chapter on covert pens. An example recipe:
‘Chinese Red Secret Ink’. Used by agents of the Chinese Ministry of Public Security, this ink is made by mixing one part each of phenolphthalein, glycerin, alcohol, and carbon tetrachloride. When dry, it is colorless, but upon application of ammonia, it turns reddish. It disappears again when the ammonia vaporizes.