Password management is challenging, even for famous magicians. Teller, of Penn & Teller, tries to conjure a viable system
When the client wrote on the first sheet, the pressure left an invisible copy in wax (today, we use soap) on the second sheet. The medium took back the pad, left the room to “get a glass of water” (or, in my case, to fetch the frosty frappés) and secretly dusted the wax impression with powdered lead (I use something less lethal). The dusty particles stuck to the residue and revealed the writing.