Invisible Ink; Not just for Joke Shops?

In the spirit of Halloween I decided to share a recipe which might be fun for adults and kids to play with at home.  It’s from The Good Wife’s Guide or Le Menagier de Paris, written in late 14th century France.  The author is unknown, although we are supposed to believe it was written by an older Parisian merchant to his fifteen year old bride.  The book has many useful snippets of information, such as how to set tables, hire servants, behave in church, etc.  plus recipes which include sausages, sauces, rosewater, and invisible ink.  That is the recipe I’ll share today.

#323 To write a letter on paper that stays invisible to everyone unless the paper is heated, moisten and dissolve some ammonium salt in water, write with it, and let dry.  It will last about eight days.”–Le Menagier de Paris (Good Wife’s Guide)

This recipe might sound familiar to those of us who did a similar trick in junior high science class.  The principal is the same, although we used lemon juice & water back then.  For those of you who wish to try this recipe at home, you can use baking powder, which has ammonium salt as an active ingredient.  In Canada, you can purchase a bottle of Buckley’s cough syrup (which uses ammonium salt as an active ingredient and play around with it.

I mixed about a teaspoon of baking powder in some water and painted my image onto a sheet of paper, waited for it to dry, and got this result;


Source;The Good Wife’s Guide (Le Menagier de Paris).  Greco, Gina L. & Christine M. Rose, trans.  Cornell University Press; Ithaca, New York, 2009.  ISBN 978-0-4738-9


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