In a 2015 episode of Turn, a US Revolutionary War TV drama on AMC, George Washington’s spy Abraham Woodhull uses a special ink made with alum to write secret messages under the shells of hard-boiled eggs. The technique was also advertised on the show’s Twitter in 2014, a year before the episode aired (Figure 1).
— Turn AMC (@TurnAMC) May 15, 2014
Turn is based on a 2006 book by Alexander Rose called Washington’s Spies: The Story of America’s First Spy Ring, but there is no mention in the book of any such technique. Instead, it seems to come from a 2009 book by John A. Nagy, Invisible Ink: Spycraft of the American Revolution. That book describes an ink that is able to permeate the shell of a hard-boiled egg, leaving the message hidden inside and no trace of writing on the shell. It is not attributed to George Washington and his spies, however, but to Giambattista della Porta. Nagy writes:
“In the fifteenth century Italian scientist Giovanni Porta described how to conceal a message in a hard-boiled egg. An ink is made with an ounce of alum and a pint of vinegar. This special penetrating ink is then used to write on the hard-boiled egg shell. The solution penetrates the shell leaving no visible trace and is deposited on the surfaced of the hardened egg. When the shell is removed, the message can be read.” (John A. Nagy, Invisible Ink: Spycraft of the American Revolution, 2009: 7)
Nagy’s account of della Porta’s recipe seems in turn to have come from 1999 book by Simon Singh called The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography. Singh, however, leaves it unclear whether the egg is to be hard-boiled or raw when one writes on it:
“In the fifteenth century, the Italian scientist Giovanni Porta described how to conceal a message within a hard-boiled egg by making an ink from a mixture of one ounce of alum and a pint of vinegar, and then using it to write on the shell. The solution penetrates the porous shell, and leaves a message on the surface of the hardened egg albumen, which can be read only when the shell is removed.” (Simon Singh, The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography, 1999: 10)
Singh’s description of della Porta’s recipe only appears in the first edition of The Code Book. In later editions it is missing without comment. The reason might be found by reading della Porta himself, who in Book 16 chapter 4 of his Natural Magic mentions the technique, but neither claims to have invented it nor to have gotten it to work:
“Africanus teaches thus: ‘grind [oak] galls and alum with vinegar, until they have the viscosity of ink. With it, inscribe whatever you want on the egg and once the writing has been dried by the sun, place the egg in sharp brine, and having dried it, cook it, peel, and you will find the inscription.’ I put it in vinegar and nothing happened, unless by ‘brine’, he meant sharp lye, what’s normally called capitellum” (della Porta, Magia Naturalis 16.4: Latin 1590, English 1658)
Della Porta attributes the recipe to Africanus, probably Sextus Julius Africanus, a 2nd–3rd century CE traveler, writer and chronicler, whose recipe for an egg-permeating ink is preserved in the 10th century Greek compilation known as the Geoponica, of which della Porta’s recipe is a literal Latin translation. Unlike Singh’s or Nagy’s recipe, della Porta’s includes oak gall (an ingredient often found in inks as a pigment) and lacks precise measurements.
The measurements and techniques described by Singh seem similar to a recipe printed on page 143 of the 1973 New Earth Catalogue (Figures 2 and 3):
This recipe uses half the amount of vinegar. It also mentions that a small brush is to be used and says to boil the egg for 15 minutes. None of these details are in Singh’s or in della Porta’s version.
This recipe shares a strong family resemblance to a one published by the USDA in 1965, whose purpose was to get children to eat more eggs. We know this because the USDA’s suggestion was picked up by the New York Times and published on page 14 of the 29 May 1965 issue (Figure 4):
Sometime between 10 and 20 years earlier, either in 1946 or 1959, a similar version similarly targeted to children was published in volume 14 of Richards Topical Encyclopedia, an encyclopedia ordered by theme that was sold door to door in the US (Figure 5).
Another 10 (or 20) years before that, we find the recipe on page 58 and 132 of the February 1936 issue of American Druggist. A reader from Oregon asks for the recipe of a solution used to mark eggs. The editor replies that the “trick” is described ‘in Henley’s “Book of Recipes”.’ (Figure 6)
The editor’s recipe is not obviously the one “Oregon” was after (it includes neither sugar nor acid) but the details are familiar: 1 oz alum, 8 oz (= 1 cup = 1/2 pint) vinegar, a small, pointed brush, 15 minutes boiling. Some details are new: we’re told the brush should be camel’s hair (I will come back to this in the sequel).
The editor of American Druggist also gives a source: Henley’s “Book of Recipes”. The Norman W. Henley Publishing company was active in the United States in the early 20th century and beginning in 1907 published almost yearly editions of an extremely popular book of household recipes: Henley’s Twentieth Century Book of Recipes, Formulas and Processes: Containing Nearly Ten Thousand Selected Scientific, Chemical, Technical and Household Recipes, Formulas and Processes for Use in the Laboratory, the Office, the Workshop and in the Home By Gardner D. Hiscox.
I checked the 1907 edition of Henley’s, but found nothing. I continued looking for references to the recipe closer in time to the American Druggist issue to refine the search. I found two earlier instances: page 97 of the January 1930 issue of Popular Science, and (slightly earlier) page 110 of the September 1929 issue of Field and Stream, where it is referred to as ‘an old hex trick’ (Figures 7 and 8):
If Henley’s was the ultimate source, the recipe had to have appeared sometime before 1929. I checked the 1925 edition, but it was nowhere to be found. The next edition was published in 1929, the same years as the Field and Stream recipe. There it was on page 786 (Figures 9 and 10):
The recipe contains many of the characteristics of the one that has been passed down in American lore and attributed in one form or another to George Washington’s spies or Giambattista della Porta: 1 oz. alum, ½ pint vinegar, a small brush, 15 minutes of boiling.
Given the reach of Henley’s “Book of Recipes” in the US, this is not surprising. But Henley’s recipe also lacks a key ingredient from the recipe that della Porta attributed to Africanus: oak gall. How and when this ingredient dropped out from a recipe reliably passed down for over a thousand years is another story.
This post continues a study of how a 3rd century recipe for a magic ink, despite the fact that it probably never worked, still managed to work its way into American popular culture in the 20th and 21st centuries. An earlier part of the study is posted here.