A 16th century alchemist at work in the ante-room of his laboratory, fixing a portion of his apparatus. On the table is his luting box and knife. His laboratory is visible through the window with various-sized stills.
Understanding the Language of Alchemy - Medievalists.net
Giovanni Battista della Porta in "De furtivis literarum notis" suggested, amongst other ways of 'secret' communication, pointing at different parts of the body to indicate letters. (For cryptography geeks, his book also includes Alberti's Cipher Disk!)