{"id":830,"date":"2024-02-11T23:05:51","date_gmt":"2024-02-11T23:05:51","guid":{"rendered":"https:\/\/sites.rutgers.edu\/motley-emblem\/?p=830"},"modified":"2024-02-19T22:48:09","modified_gmt":"2024-02-19T22:48:09","slug":"optical-brighteners-paper","status":"publish","type":"post","link":"https:\/\/sites.rutgers.edu\/motley-emblem\/optical-brighteners-paper\/","title":{"rendered":"Optical Brighteners: Paper"},"content":{"rendered":"

When we think of paper, especially historical paper, we tend to think of white paper.\u00a0 We think of the fine white paper used for books, or for letters or manuscript notes or diaries or accounting– and lots of that paper was being made by the eighteenth century.\u00a0 But yet more paper was being used for other things, including printing of documents not designed to be saved– like newspapers– or for any purpose where a soft, cheap, flexible medium would do.\u00a0 So: for every sheet of paper used to print a novel or to write a letter, there were ten or more used for scribbling accounts, or enclosing things for shipping, or wrapping packages like sugar or fabrics or medicines, or oiling for windows, or lining pie-sheets, and so forth.<\/p>\n

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In his retirement, British painter Jonathan Richardson endlessly repeated portraits of himself, many on blue paper. Self-Portrait <\/em>(1729) Met AN 2012.45<\/figcaption><\/figure>\n

But that sense of most paper as being white is relatively recent.\u00a0 Paper in eighteenth-century Europe was overwhelmingly made from recycled linen rags.\u00a0 And, in the absence of effective chemical bleaches, to make the best paper, they needed the very cleanest ragstock.\u00a0 As you can probably imagine, that sort of linen, discarded as unfit for use, but still white, was also the rarest.\u00a0 So most of that linen went to make less desirable paper, like the kinds known as “brown” or “whitey-brown.”\u00a0 This was still useful for wrapping packages or preparing things for mailing, and so on, since it had all the strength and flexibility of paper.\u00a0 It just wasn’t as useful for writing.\u00a0 A further batch of mildly soiled paper could solve the problem in a different way– by being dyed or stained.\u00a0 Mid-range paper dyed with indigo, for instance, was commonly used to wrap products like sugar and flour; it also came into vogue as a medium for pastels.\u00a0 The artist Jonathan Richardson sketched endless self-portraits on blue paper.\u00a0 Sometimes he used discarded wrappers, and sometimes purchased new wrapping paper especially for that purpose.<\/p>\n

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Paper pulp repeatedly passes between the cutting cylinder (viewed from above) and the bedplate on which it rests. Image from Lalande, Art de faire le papier<\/em> (1761).<\/figcaption><\/figure>\n

But that bluing– that also suggested another strategy, which came to characterize paper from Holland.\u00a0 Papermakers in Holland faced a problem of elevation, since that country is almost entirely at sea-level.\u00a0 The problem of power they overcame by developing a cylindrical machine that could be driven by wind.\u00a0 That machine is called a Hollander, and the cellulose of the paper in the Motley Emblem passed through one.\u00a0 But without lots of clean, relatively pure water, Dutch paper tended to be slightly yellow when compared with the creamy-white paper from the mountainous region of France.<\/p>\n

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Sterne’s page, at high magnification.\u00a0 Small flecks of nearly-black pigment may suggest that Sterne’s page was treated with indigo.\u00a0 Photograph by author at the Getty Villa conservation lab.<\/figcaption><\/figure>\n

Dutch papermakers therefore sometimes treated the rag-pulp for high-grade writing papers with a nearly-transparent tincture of indigo.\u00a0 That pale blue additive filled out the yellowish spectrum, returning something closer to white.\u00a0 In time, what began as a workaround to approach the cream-color of French paper wound up being desirable in its own right, akin even to a trademark.\u00a0 Dutch paper, soft and thick, was sought for its blueish cast.<\/p>\n

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Synthetic brighteners, like 2,5-Bis(5-tert<\/i>-butyl-benzoxazol-2-yl)thiophene,<\/span> are now nearly ubiquitous in paper and white cloth. [click for source.]<\/figcaption><\/figure>Nowadays, a new sort of optical brightener is commonly used.\u00a0 This sort of brightener is found in nearly all white fabrics, paper, and even in detergents\u2014which leave behind chemicals that whiten our whites.\u00a0 Unlike the Dutch method, however, our modern brighteners work with light that is not in the visible range.\u00a0 When we say that a chemical reagent reflects light, we are really describing a two-stage process.\u00a0 It absorbs photons in one wavelength, and then emits photons in another one\u2014always returning something less energetic than what it absorbed.\u00a0 So, chemical brighteners absorb light in the ultraviolet range, which we cannot see, and return lots of bluish white light in a range that we can.\u00a0 This is why modern paper, or brightened cloth, can seem to glow; it is returning, in the visible range, all the light we cannot see.<\/p>\n

This has some interesting side effects– one of which has started to create a problem for this historical reconstruction.\u00a0 Last summer, I worked with a Philly-based papermaker to prepare a few trial batches of linen-rag paper.\u00a0 We began with what we thought was raw linen cloth, painstakingly cutting it in to small squares, then boiling it with an alkali, <\/span>running it through a Hollander<\/a>, and making a series of trial sheets, just as the Dutch papermakers had done in preparing the paper that would wind up in Sterne’s book.\u00a0 I knew nothing, then, about optical brighteners, or that they would cling even to microscopic fibers through the whole process of cooking, macerating, and sheet formation.<\/span><\/p>\n

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Pigment mockup, fluorescing under ultraviolet light. Photo by author at Getty villa.<\/figcaption><\/figure>\n
\"\"<\/a>
Pigment mockup, under natural light. Photo by author at Getty Villa.<\/figcaption><\/figure>\n

But they did– and this makes that batch of paper useless for this project.\u00a0 Take, for instance, tests recently ran using the sort of ultraviolet instrument forensic detectives employ.\u00a0 We were hoping to find, or to rule out, the presence of a handful of organic pigments which are known to fluoresce in the visible range when illuminated with ultraviolet light.\u00a0 Those pigments appear not to be present.\u00a0 What is obvious, however, are those optical brighteners\u2014have made the mock-up nearly useless.<\/p>\n

Brighteners, in other words, now present an adulterant on the order of the adulterants which Dutch papermakers worked so hard to exclude.\u00a0 They are now nearly ubiquitous, embedded in raw cloth and included in nearly all detergents.\u00a0 And because the goal of this project is to make sheets accurate enough to fool the usual techniques for pigment-identification, our next steps, therefore, involve finding a cellulose source untreated with brighteners.\u00a0 Like the Dutch, we must acquire linen rags which are clean of adulterants which the eye can see, like good old-fashioned dirt.\u00a0 But, unlike them, we must also find ones which are free of invisible adulterants, including the chemicals we use to create the illusion of cleanliness.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

When we think of paper, especially historical paper, we tend to think of white paper.\u00a0 We think of the fine white paper used for books, or for letters or manuscript … Read More<\/a><\/p>\n","protected":false},"author":136,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-830","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"acf":[],"yoast_head":"\nOptical Brighteners: Paper - The Motley Emblem<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/sites.rutgers.edu\/motley-emblem\/optical-brighteners-paper\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Optical Brighteners: Paper - The Motley Emblem\" \/>\n<meta property=\"og:description\" content=\"When we think of paper, especially historical paper, we tend to think of white paper.\u00a0 We think of the fine white paper used for books, or for letters or manuscript … Read More\" \/>\n<meta property=\"og:url\" content=\"https:\/\/sites.rutgers.edu\/motley-emblem\/optical-brighteners-paper\/\" \/>\n<meta property=\"og:site_name\" content=\"The Motley Emblem\" \/>\n<meta property=\"article:published_time\" content=\"2024-02-11T23:05:51+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2024-02-19T22:48:09+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/sites.rutgers.edu\/motley-emblem\/wp-content\/uploads\/sites\/786\/2024\/02\/Richardson-Self-Portrait-scaled.jpg\" \/>\n<meta name=\"author\" content=\"Sean Silver\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Sean Silver\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"5 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/sites.rutgers.edu\/motley-emblem\/optical-brighteners-paper\/\",\"url\":\"https:\/\/sites.rutgers.edu\/motley-emblem\/optical-brighteners-paper\/\",\"name\":\"Optical Brighteners: Paper - The Motley Emblem\",\"isPartOf\":{\"@id\":\"https:\/\/sites.rutgers.edu\/motley-emblem\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\/\/sites.rutgers.edu\/motley-emblem\/optical-brighteners-paper\/#primaryimage\"},\"image\":{\"@id\":\"https:\/\/sites.rutgers.edu\/motley-emblem\/optical-brighteners-paper\/#primaryimage\"},\"thumbnailUrl\":\"http:\/\/sites.rutgers.edu\/motley-emblem\/wp-content\/uploads\/sites\/786\/2024\/02\/Richardson-Self-Portrait-scaled.jpg\",\"datePublished\":\"2024-02-11T23:05:51+00:00\",\"dateModified\":\"2024-02-19T22:48:09+00:00\",\"author\":{\"@id\":\"https:\/\/sites.rutgers.edu\/motley-emblem\/#\/schema\/person\/21ed676e09a499d50cd77d10cd4c576c\"},\"breadcrumb\":{\"@id\":\"https:\/\/sites.rutgers.edu\/motley-emblem\/optical-brighteners-paper\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/sites.rutgers.edu\/motley-emblem\/optical-brighteners-paper\/\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/sites.rutgers.edu\/motley-emblem\/optical-brighteners-paper\/#primaryimage\",\"url\":\"https:\/\/sites.rutgers.edu\/motley-emblem\/wp-content\/uploads\/sites\/786\/2024\/02\/Richardson-Self-Portrait-scaled.jpg\",\"contentUrl\":\"https:\/\/sites.rutgers.edu\/motley-emblem\/wp-content\/uploads\/sites\/786\/2024\/02\/Richardson-Self-Portrait-scaled.jpg\",\"width\":1561,\"height\":2560,\"caption\":\"After retiring as a portraitist, Jonathan Richardson, endlessly repeated portraits of himself, many on blue paper. 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