1. In September 1656, a female spy based in England wrote to her brother, who was living under exile in Antwerp. She feared their letters were being intercepted, broken into and sealed up again with counterfeit seals before being sent on their way. She urged caution: only ‘let mee know your minde—By the olde way [,] the hartichockes [,] as soone as you cane’. Her directive to communicate by artichokes seems peculiar, but it is possibly hinting at a recipe of invisible ink, concocted ‘by the olde way’, a phrase that refers either to folk wisdom, or even some measure of witchcraft. To test whether it was possible to turn artichoke juice into a useable invisible ink we chose globe artichokes, because those are native to the old world and allow for a second harvest in the autumn, when our cunning spy wrote her letter.

    The juice of a mashed-up, raw artichoke can instantaneously be used as invisible clear ink: the secret writing is revealed when the paper was exposed to the heat of the open flame of a candle.

    Produced by MIT Video Productions (MVP). Directed by Jana Dambrogio, Thomas F. Peterson (1957) Conservator, MIT Libraries and Dr Nadine Akkerman, lecturer in English at Leiden University.

    Funded by the Netherlands Organization for Scientific Research (NWO), VENI-project “Female Spies”, and the Massachusetts Institute of Technology (MIT) Libraries.

    Special thanks to MITemp Elizabeth Mauer; she researched and demonstrated this technique in the video. Many thanks also to MIT Libraries Conservation Associate Ayako Letizia, MIT senior Jacky Martin, and MITemp Leslie To, Curation and Preservation Services, MIT Libraries; Bob Edwards MIT Environmental Health and Safety Representative; and Pete Langman.

    Cite as: Jana Dambrogio, Nadine Akkerman, Elizabeth Mauer, et al. ‘Invisible Ink: Artichoke Juice, Invisible Ink --a Witchcraft Potion? (1656)’, Letterlocking Instructional Videos. Filmed: May 2015. Duration: 2:56. Posted: November 2015. Video URL: [Use URL below]. Date accessed: [Date].

    Copyright 2016. Jana Dambrogio, Nadine Akkerman and Massachusetts Institute of Technology (M.I.T). All rights reserved. The following copyrighted material is made available under the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) License creativecommons.org/licenses/by-nc/4.0/. Contact the M.I.T. Technology Licensing Office for any other licensing inquiries.

    Interested in spies and their secrets? See also Nadine Akkerman, Invisible Agents: Women and Espionage in Seventeenth-Century Britain (Oxford: Oxford University Press, 2018) global.oup.com/academic/product/invisible-agents-9780198823018?cc=us&lang=en&;

    NB: Please create and reveal invisible inks responsibly. Be mindful of open flames or hot tools in the workspace.

    @letterlocking
    letterlocking.org
    libraries.mit.edu/preserve
    brienne.org
    Follow our collaborators on Twitter @misswalsingham @NWOHumanities @MITLIbraries @LeidenHum

    The URL for this video: vimeo.com/letterlocking/artichoke

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  2. By her correspondent’s panic reaction at having lost her letter with the formula for “invisable [sic] ink”, one can safely assume that one female spy had recommended a more sophisticated potion, not plain lemon juice, for secret messages. Indeed, spies did not have to rely on a steady stream of juicy lemons to write invisible messages, as Giambattista della Porta’s “Magiae Naturalis” provided another recipe, one that worked on textiles as well as paper. His instructions headed "That dipping a Linen rag in water, the letters may appear" reads as follows in translation: ‘Dissolve Alom in water, and with it make letters upon white Linen, sheets, napkins, and the like. For when they are dry, they will presently vanish. When you will have the visible, soak them in water, and the Linen will seem to be darkened. But only where the Alom has written, it will not. For the letters will grow so clear, the you may read them’ (Book 16, Chapter 1).

    Alum-ink is heat but also water activated, depending on the material that you are writing on.

    First, 0.03g of alum in 20 mL of water creates an ink useable to write on paper: the secret writing reveals itself when the paper is exposed to the heat of the open flame of a candle or when the paper is placed in water. The latter reveal has the advantage of the writing disappearing again once the paper dries up.

    Second, the same solution is also most suitable to write on fabric, as Porta indicates, in particular on linen but also cotton. NB the ink needs to soak into the fabric enough so that the wetness of the ink is visible on the verso side. If the written words are sitting on top of the fabric only, it will not work. The secret message reveals itself when placed in water, but disappears again once the textile dries up.

    A stronger solution— 1.0g of alum in 20 mL—allows for a more dramatic fabric reveal, but it will leave the textile harder in the areas where the ink solution is applied, possibly drawing attention to the surreptitious, illicit concealing.

    What did we learn in general for invisible inks that need to be revealed with heat?

    Two tips: one, have a cut edge and not a torn edge for the paper source. The torn edges leave paper microfibers free and available to catch fire when held over a flame. Two, write your note towards the center of the paper and not near the edges because edges are more vulnerable to catch on fire when the paper is held directly over the open flame.

    We also experimented with John Cotgrave's recipe. Turning the pages of Cotgrave’s “Wits Interpreter” (1655), spies would not only discover one of Cardinal Richelieu’s cipher keys, but also a alum-based formula for invisible ink: ‘dissolve a little Allum in water, and with your pen dipt in the water write your letter on paper, which being dryed, there appears nothing, but being dipt in water, the words may be plainly read.’ We brush applied onto handmade paper a solution of 0.5 grams of alum dissolved in 20mL of water and allowed our message to dry. We cut the message in three and immersed each slip of paper into three temperatures of water--hot, tepid, and cold--to see if the temperature affected the reveal. Indeed all three temperatures worked. The messages were invisible after we allowed all three papers to dry. Search for #SecretWritingTechniques and see the results of this experiment.

    Produced by MIT Video Productions (MVP). Directed by Jana Dambrogio, Thomas F. Peterson (1957) Conservator, MIT Libraries and Dr Nadine Akkerman, lecturer in English at Leiden University.

    Funded by the Netherlands Organization for Scientific Research (NWO), VENI-project “Female Spies”, and the Massachusetts Institute of Technology (MIT) Libraries.

    Thanks to Elizabeth Mauer who researched and demonstrated this technique; Ayako Letizia, Wunsch Conservation Lab Conservation Associate; Jacky Martin, Leslie To; Bob Edwards; and Pete Langman.

    Cite as: Jana Dambrogio, Nadine Akkerman, et al. ‘Spies and secrets: Alum Invisible Ink’, Letterlocking Instructional Videos. Filmed: May 2015. Duration: 7:18. Posted: November 2015. Video URL: [Use URL below]. Date accessed: [Date].

    Copyright 2016. Jana Dambrogio, Nadine Akkerman and Massachusetts Institute of Technology (M.I.T). All rights reserved. The following copyrighted material is made available under the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) License creativecommons.org/licenses/by-nc/4.0/. Contact the M.I.T. Technology Licensing Office for any other licensing inquiries.

    @letterlocking
    letterlocking.org
    Follow our collaborators on Twitter @misswalsingham @NWOHumanities @MITLibraries @LeidenHum

    See also Nadine Akkerman, Invisible Agents: Women and Espionage in Seventeenth-Century Britain (Oxford: Oxford University Press, 2018) global.oup.com/academic/product/invisible-agents-9780198823018?cc=us&lang=en&;

    The URL for this video: vimeo.com/letterlocking/alum

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  3. In December 1657 the circle of James Butler (1610-88), Marquess of Ormond, used a recipe they had received from Lord Ogleby, which after testing they found most effective to delude the Cromwellian regime: ‘ye secret that L. Ogleby gaue (namely the powder of gall in water, to be washd ouer wth ye powder of calcined copperas) is not discouered, but may be safely used.’

    Produced by MIT Video Productions (MVP). Directed by Jana Dambrogio, Thomas F. Peterson (1957) Conservator, MIT Libraries and Dr Nadine Akkerman, lecturer in English at Leiden University.

    Funded by the Netherlands Organization for Scientific Research (NWO), VENI-project “Female Spies”, and the Massachusetts Institute of Technology (MIT) Libraries.

    Special thanks to MITemp Elizabeth Mauer; who helped to research this technique. Many thanks also to MIT Libraries Conservation Associate Ayako Letizia, MIT senior Jacky Martin, and MITemp Leslie To, Wunsch Conservation Lab, MIT Libraries; Bob Edwards MIT Environmental Health and Safety Representative; Sara Fujiko Powell, and Pete Langman.

    Cite as: Jana Dambrogio, Nadine Akkerman, et al. ‘Gall Invisible Ink (reveal: Copper II Sulfate or Iron II Sulfate) (1657)’, Letterlocking Instructional Videos. Filmed: May 2015. Duration: 4:01. Posted November 2016. Video URL: [Use URL below]. Date accessed: [Date].

    Copyright 2016. Jana Dambrogio, Nadine Akkerman and Massachusetts Institute of Technology (M.I.T). All rights reserved. The following copyrighted material is made available under the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) License creativecommons.org/licenses/by-nc/4.0/. Contact the M.I.T. Technology Licensing Office for any other licensing inquiries.

    NB: Please create and reveal invisible inks responsibly. Be mindful of open flames or hot tools in the workspace.

    Interested in spies and their secrets? See also Nadine Akkerman, Invisible Agents: Women and Espionage in Seventeenth-Century Britain (Oxford: Oxford University Press, 2018) global.oup.com/academic/product/invisible-agents-9780198823018?cc=us&lang=en&;

    @letterlocking
    letterlocking.org
    libraries.mit.edu/preserve
    brienne.org
    Follow our collaborators on Twitter @misswalsingham @NWOHumanities @MITLIbraries @LeidenHum

    The URL for this video: vimeo.com/letterlocking/gall2

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  4. 2.0g gum arabic crystals
    10.0g of oak galls
    2.5g iron sulfate

    1. Dissolve the gum arabic in water making a light, sticky solution, set aside.
    2. Crush two galls (they look like nuts) with a hammer. Place them in a litre beaker and cover with 75 ml of water overnight to create a nice brown colored solution. Filter out the solids.
    3. Dissolve two teaspoons of iron sulfate in 45ml of water, set aside. The blue green crystals will turn to a muddy brown color as they dissolve into solution, set aside.
    4. Mix the gall and sulfate solutions, it should produce a lovely dark blue black.
    5. Add your gum arabic solution to the ink to give it some thickness.

    Shape your quill and write!

    Produced by MIT Video Productions (MVP). Directed by Jana Dambrogio, Thomas F. Peterson (1957) Conservator, MIT Libraries, Dr Nadine Akkerman, lecturer in English at Leiden University, and Joe McMasters, Senior Producer of MIT Video Productions.

    Funded by the Netherlands Organization for Scientific Research (NWO), VENI-project “Female Spies”, and the Massachusetts Institute of Technology (MIT) Libraries.

    Many thanks to MIT Libraries Conservation Associate Ayako Letizia for preparing and demonstrating how to make and write with the iron gall ink; to Phoebe Dent Weil, Birgit Reissland, and Rich Spelker for their expertise and assistance in providing historic ink recipes.

    Cite as: Jana Dambrogio, Nadine Akkerman, et al. ‘Iron Gall Ink: A Quick and Easy Method’, Historic Ink Technology Instructional Videos. Filmed: Sep 2014. Duration: 4:45. Posted: Dec 2014. Video URL: [Use URL below]. Date accessed: [Date].

    Copyright 2016. Jana Dambrogio, Nadine Akkerman and Massachusetts Institute of Technology (M.I.T). All rights reserved. The following copyrighted material is made available under the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) License creativecommons.org/licenses/by-nc/4.0/. Contact the M.I.T. Technology Licensing Office for any other licensing inquiries.

    Interested in spies and their secrets? See also Nadine Akkerman, Invisible Agents: Women and Espionage in Seventeenth-Century Britain (Oxford: Oxford University Press, 2018) global.oup.com/academic/product/invisible-agents-9780198823018?cc=us&lang=en&;

    NB: Letterlock responsibly. Be mindful of open flames or hot tools.

    @letterlocking
    letterlocking.org
    libraries.mit.edu/preserve
    brienne.org
    Follow our collaborators on Twitter @misswalsingham @NWOHumanities @MITLIbraries @LeidenHum

    The URL for this video is: vimeo.com/letterlocking/irongallink

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