2014 Invisible Ink Chemistry

A reprint from American Scientist the magazine of Sigma Xi, The Scientific Research Society This reprint is provided for personal and noncommercial use. For any other use, please send a request to Permissions, American Scientist, P.O. Box 13975, Research Triangle Park, NC, 27709, U.S.A., or by electronic mail to [email protected]. ©Sigma Xi, The Scientific Research Society and other rightsholders The Hidden Past of Invisible Ink Often synonymous with international espionage, secret writing also had a long- forgotten heyday in stage magic and science demonstrations. Kristie Macrakis or many people, the words in- It was a heady time, an era when valleys. Until the 16th century, Schnee- visible ink readily conjure up popular science became intoxicating— berg was known as a a silver-mining images of childhood fun with low-tech entertainment in a low-key town, but after workers depleted the lemon juice and a candle, or spy world. But other historical and cultural known veins of that metal they turned Fmessages during wartime. And there is circumstances carried the inks to 20th- their attention to cobalt, which was in a good reason for this association, be- century America, and ultimately into high demand for coloring glass and cause secret writing has long been part modern popular culture. other goods. Miners removed hun- of the worlds of both magical entertain- dreds of thousands of kilograms of ment and international intrigue. But it Invisible Landscapes cobalt from the mountain. Streets such also has an overlooked long, colorful, I’ve been fascinated by the history of as Silver Road and Cobalt Road still and little-known history. invisible ink for a number of years, and snake through the Schneeberg land- The tale begins with the discovery of a have even worked with my colleague scape and define its past. Although sil- magical appearing and disappearing ink, Jason Lye, a color chemistry expert, to ver brought riches to the town, cobalt and crests with a convergence of trends re-create some traditional ink formulas. produced many more exotic marvels— during the end of the Enlightenment in That is why I was excited when, a few including invisible ink. the 18th century. During that era of in- years ago, I had the opportunity to visit The 16th century was the heyday of tellectual ferment, a rise of stage magic Schneeberg, Germany (below), one of “books of secrets,” compilations of tech- coincided with a revival of so-called the birthplaces of these magical sub- nical and medicinal recipes and magic © 2014 Museum of Fine Arts, Boston © 2014 Museum of Fine natural magic—an occult tradition that stances, and a rich source of inspiration formulas. These books occasionally in- sought power from natural sources, such for modern chemistry. cluded directions for creating invisible as herbology and astrology—alongside I have fond memories of hiking up ink, written as a basic kitchen recipe an increased demand for public scien- and down the trails surrounding that using simple and readily available in- tific demonstrations. It was against the mountaintop village, where shop win- gredients. For example, a recipe would backdrop of this witches’ brew of cir- dows are filled with hand-carved nut- suggest dipping an alum-written let- cumstances that invisible ink flourished. crackers, smoking men, candelabras, ter in water, where the writing would angels, and pyramids. Villagers there turn from white to black; or it might ad- still use the miners’ greeting Glück vise rubbing powder on fig-tree milk Kristie Macrakis is a professor of history, technol- auf!—Godspeed—and the hammer to make it visible. Other directions ad- ogy, and society at the Georgia Institute of Technol- and pick symbol still decorates knick- vised the experimenter to paint, sponge, ogy. She received her Ph.D. in the history of science knacks, buildings, walls, and fences. or spray a liquid on the secret letter, or from Harvard University, and also specializes in the It is easy to imagine the music of wave it in the air, sprinkle powder on it, history of espionage. She is the author or editor of Bach wafting through the cobblestone hold it over fire, or dip it into water, de- five books, including Seduced by Secrets: Inside streets of this Baroque village. pending on what kind of ink was used the Stasi’s Spy-Tech World (Cambridge Universi- ty Press, 2008). Her latest book is Prisoners, Lov- Located in the Saxon Ore mountain to write the invisible message. ers, and Spies: The Story of Invisible Ink from range, the Schneeberg Mountains once Cobalt allowed invisible ink to be- Herodotus to al-Qaeda (Yale University Press, contained rich sources of silver, bis- come much more advanced. In 1705 a 2014), from which this article is adapted. Internet: muth, and cobalt hidden beneath the mysterious female German alchemist http://www.kristiemacrakis.com bucolic exterior of verdant hills and seems to have been the first person to 198 American Scientist, Volume 102 © 2014 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact [email protected]. Although invisible ink came into its modern usage largely would heat the card to show the hidden image, now turned via Europe, other cultures have also delighted in its magical brown (a method called aburidashi in Japanese). This print is properties. Woodcut prints like this one from the Edo pe- likely inspired by the legend of Jiraiya, a samurai who could riod (1603–1867) in Japan were sold at festivals; the purchaser magically morph into a giant toad. identify bismuth-cobalt as a valuable color changed from rosy red to grassy rable by eyes that sparkled with liveli- substance from which to make invisible green to sky blue when heat was ap- ness. It is easy to imagine a twinkle in his ink. This alchemist was also the anony- plied. When the cobalt was prepared eyes when he started playing with this mous author of three books, including and turned into a solution with which unusual new substance. one with the alluring title On the Key to to write, it was clear, but it produced a In the summer of 1736, the anony- the Cabinet of the Secret Treasure Room of fabulous blue-green color when heated. mous German artist mentioned by Hel- Nature, which included a discussion of The writing disappeared when cooled. lot showed some members of the Royal the changing bismuth-cobalt colors. The Jean Hellot (1685–1766), the French Academy of Sciences in Paris the magi- author’s name was listed only by the ini- scientist who did more than anyone else cal cobalt phenomenon. The artist had tials DJW. Historical research has shown to investigate, promote, and advance the climbed the hills of Saxony in search of that she might have been Dorothea Juli- subject of invisible ink during the 18th the source rock. He dubbed it Minera ana Walchin (or some other form of the century, referred to another person—an Marchassitae, based on a general term name, such as Wallich or Wallichin), but artist, name also unknown—when al- for ore including bismuth, cobalt, iron, little else is known about her. locating credit for the discovery of the and other minerals. The curious prop- This obscure woman alchemist magical qualities of cobalt. Hellot lived erties of this material enchanted Hellot, seems to have discovered a cobalt most of his professional life as an indus- who experimented assiduously during mineral that appeared red in a solu- trial chemist during the early period his leisure time. By the next summer he tion and was supposed to be the “first of the French Enlightenment. He was had written a paper on the subject for matter” from which all other elements a pioneer in the technical chemistry of the Academy’s journal. formed—the Holy Grail for the al- dyeing, mining, and assaying. Contem- Soon after Hellot’s pathbreaking pa- chemists. The cobalt mineral also dis- porary accounts refer to him as a short per was published, German scientists played remarkable visual qualities: Its and rather chubby man, made memo- objected that a Frenchman got credit www.americanscientist.org © 2014 Sigma Xi, The Scientific Research Society. Reproduction 2014 May–June 199 with permission only. Contact [email protected]. Johannes Balthasar Friderici’s treatise on cryptography, published in Germany in 1684, in- cludes instructions for the prepa- ration and use of invisible ink. The frontispiece features Mars, the god of messaging, flying through scenes of codes and invisible writing. from his scientific friends in different countries. Hellot became so enchanted with cobalt’s varied color possibilities that he started thinking about painting landscapes with the inks or dyes. He dreamed of creating a winter landscape that would transform instantly into a springtime scene when it was heated. The idea caught on, and continued to captivate three common developer types as de- the public for the next two centuries. for “discovering” this substance as a scribed by della Porta. Hellot also added By around 1746, sympathetic ink was new phenomenon. They claimed that two new categories of his own. In the fashionable in Paris, and changeable a Professor Teichmeyer in Jena had, first new type, air developed some dyes, landscape fire screens became all the in fact, first demonstrated the same and in the second one, some inks simply rage. A barren winter landscape with cobalt ink to his students six years appeared and disappeared spontane- tree trunks and branches was painted earlier. Of course, there was also that ously. The common denominator of all on a fire screen with ordinary India mysterious German lady who had de- the old secret-writing pairings was that ink.

Load more