There are four types of specialty papers which appeared during this period: 1) "hydrographic" papers, which contain the dried components of iron-gall ink, can be written on with water (intended to be a convenience for travelers), and a cleaner means of writing than using liquid ink;1 2) papers treated with a colorless solution such as ferrous sulfate, which reacts with another colorless solution to form colored letters ("two-solution" papers), and was presented as a clean and convenient means of writing but often perceived as a chemical novelty; 3) papers treated to enhance the color or permanence of writing or copying inks; and 4) "safety" papers containing chemicals which react with bleach, acids, or alkali used to fraudulently alter writing on documents. In use by the mid-sixteenth century, hydrographic papers were essentially writing papers with powdered ink rubbed into the surface.2 Two-solution papers were introduced in the eighteenth century. William Lewis described an early iron/gall two-solution paper in his Commercium technicum in 1763, but stated that it was made "with a view rather to amusement than to the answering of any useful purpose."3 By 1812, manufacturers had figured out how to impregnate the paper with a solution of one ingredient, dry it, and then apply the other as a powder. The sale in Europe of papers made by this method attracted considerable attention.4 Alas, according to paper historian Joel Munsell, "it soon proved to be unworthy of notice."5 Hydrographic paper worked, but it had serious drawbacks which could account for its lack of lasting success. These include not only chemical defects in the unrefined ink, but also accidental marks made by wet hands, sneezing, or drops of sweat. Though the hydrographic and two-solution chemical papers relied most often on ferrous sulfate and gallnuts to produce their effects, later versions of both types incorporated potassium ferrocyanide for writing blue letters. In 1825, a recipe for a two-part chemical paper gave the following instructions: "Wash paper with a solution of sulphate of iron…; when written upon this paper, solution of prussiate of potass produce (sic) blue letters, and tincture of galls black ones; but upon common paper, they make colourless marks."6 Eight years later, a new commercial hydrographic paper was described by the French chemist Jean Baptiste Alphonse Chevallier: "M. Chevallier has examined a paper lately introduced, which may be written on with a pen dipt in water.…\[He\] states that similar papers may be produced by using other solutions and powders; -- thus blue is probably prepared by powdering the paper soaked in sulphate of iron with ferrocyanide of potash."7 Lewis also addressed the fading of iron-gall ink in his experiments on the "preparation of the paper for durable writing." He suggested that papermakers should imitate dyers, who boiled their cloth with nutgalls before adding ferrous sulfate;8 this produced paper of a brownish color. The same sort of color would have resulted from following John Murray's 1829 recipe for lasting writing: staining the paper with ferric chloride and writing on it with tincture of galls.9 The chemical treatment of letterpress copying papers, which was done off and on throughout the history of their use, was intended to produce a darker and more durable ink copy. The letterpress copying process worked by transfer of part of the ink from a newly written document to the back of a dampened piece of copying paper. As the copy contained only a portion of the original ink, the enhancement helped to produce legible and lasting text. James Watt's original patent for the process specified treatment with a solution containing nutgalls and calcium carbonate to oxidize and darken the ink on the copies.10 In 1787, Charles Blagden recommended using potassium ferrocyanide to restore the legibility of faded writing.11 When the Monthly Review discussed his article in 1788, the reviewer suggested a variation— that the paper be washed with the "Prussian acid." Then, "by writing with common ink on the materials so prepared, a ground of Prussian blue is formed under every stroke, and remains strong after the black has been destroyed by the weather, or discharged by acids."12 Safety papers may have had their origin in these efforts to enhance the quality of iron-gall ink writings by chemically treating writing papers. By 1789, potassium ferrocyanide had been described as an invisible ink, to be revealed by ferrous sulfate, or by chlorine,13 which perhaps suggested its use against the bleaching out of signatures and other writing on important documents. The first commercial safety paper was patented in 1817 by Gabriel Tigere. It was made by adding potassium ferrocyanide to the pulp during the last stage of papermaking, or by immersing newly made sheets of paper in a solution of it before sizing.14 This patent paper was actually used by London banks, as reported by Robert Barclay in 1860,15 but was far from perfect protection. Though safety papers have since added other features, such as microprinting and fluorescent fibers, reactive chemicals still remain part of the arsenal against forgery and fraud, and a reminder of the search for a better way of writing. ___________ notes 1. See Robert Boyle's recommendation to a court lady on this subject in his 1663 Usefulness of Experimental Philosophy. In The Works of the Honourable Robert Boyle, new ed., vol. 3 (London: Printed for W. Johnson, 1772), 417. 2. In 1562, Giovanni Baptista della Porta published a recipe for writing with water, in his Magiae nautralis (Cologne: Johanne Birckmannum and Wernerum Richvuinum, 1562), 161b; see also the powdered ink recipes in Jerome Cardan's Mediolanensis philosophi ac medici celeberrimi opervm tome 3 (Leiden: Ioannis Antonii Hvevetan, and Marci Antonii Ravavd, 1563), 256. A much more recently published recipe for hydrographic paper may be found in Fortunes in Formulas for Home, Farm and Workshop (New York and Boston: Books, Inc., 1939), 504. 3. William Lewis, Commercium philosophico-technicum (London: Printed by H. Baldwin for the Author, 1763), 395. 4. Untitled short article, Philosophical Magazine, 40 (1812): 316–317. 5. Joel Munsell, Chronology of the origin and progress of paper-making 4th ed. (Albany: J. Munsell, 1870), 59. 6. "Sympathetic inks," in The Glasgow Mechanics' Magazine 2 (1825): 217–218. A recipe for just the nutgall/ferrous sulfate method appeared in William Nicholson's entry on ink, in The British Encyclopedia vol. 3 (London: For Longman, Hurst, Rees, and Orme, 1809), Qq4. 7. "Hydrographic Paper," Philosophical Magazine, ser. 3, no. 3 (1833): 466–467. Translated from French, originally published in Journal de chimie medicale, de pharmacie et de toxicology 9 (1833): 384. 8. Lewis, 392. 9. John Murray, Practical Remarks on Modern Paper (Edinburgh: William Blackwood, 1829), 105. 10. "Specification of the Patent Granted to Mr. James Watt of Birmingham, for his New Method of Copying Letters and other Writings," The Repertory of Arts and Manufactures 1 (1794): 15–20. 11. Charles Blagden, "Some Observations on Ancient Inks, with the Proposal of a New Method of Recovering the Legibility of Decayed Writings," Philosophical Transactions of the Royal Society of London 77, no. 1 (1787): 454. 12. "Philosophical Transactions, Part II for 1787," Monthly Review, or Literary Journal 78 (1788): 189–190. 13. Lewis Brugnatelli, "Continuation of an Extract of a Letter…on some New Sympathetick Inks," The Italian Mercury 2 (1789): 66–67. 14. Reported in The Repertory of Arts, Manufactures, and Agriculture ser. 2, no. 32 (1817–18): 195–196. 15. Robert Barclay, "On the Prevention of Forgery…" Journal of the Royal Society of Arts 8 (1860): 313. Test of Gabriel Tigere's patent specification for safety paper. Whatman filter paper was soaked in a weak solution of potassium ferrocyanide, dried, then sized with gelatin. The writing is in the same iron-gall ink as in the control test. Control test for efficacy of ink erasers on unprepared handmade paper. The acids and other chemicals chosen for the test (those most often cited in the literature of the period) were used on freshly prepared iron-gall ink

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