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Low-Oxygen Encasements for Long-Term Displays

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The following is a guest post by Andrew Davis, a chemist in the Preservation Research and Testing Division (PRTD). Andrew works to understand polymeric materials in the Library’s collection, such as paper, adhesives, and audiovisual materials and also researches the effects of light and the environment on collections objects.

The Library has been expanding its visitor hours over the past few months, providing the widest reopening of its doors to the public in over two years and allowing more in-person exploration of its exhibits and reading rooms.

When it comes to seeing items on exhibit, we recently wrote about some of the testing that happens to evaluate how best to balance exhibition lighting and preservation of collection objects. Testing for light sensitivity is part of the work, however the amount of time an object spends on display, and hence its exposure to light, is also a major consideration. Some collection items are so iconic that it is assumed they will ALWAYS have light on them, as permanent displays. For example, the Library has two striking maps with this concern: the 1507 Waldseemüller world map and Abel Buell’s A New and Correct Map of the United States of North America. Other institutions think about this too. The National Archives has the Charters of Freedom. And the Smithsonian’s National Museum of African American History and Culture (NMAAHC) has the 13th Amendment and Emancipation Proclamation.

I highlight these specific objects for a reason: they all are currently being displayed in “anoxic”, or low-oxygen, display cases. You can see the 1507 Waldseemüller world map in its anoxic display here.

Wooden display cabinet showing a large map behind a window.
1507 Waldseemüller map on display in the Jefferson Building. Credit: Andrew David, PRTD.

I also mention these items and institutions because scientists in PRTD regularly collaborate with our counterparts at the National Archives and the Smithsonian to build knowledge and serve as technical leaders on anoxic display science. We have an ongoing working group of these DC-area institutions for exchanging knowledge, and we have been working on a series of white papers about encasements, the first can be read here. It also doesn’t hurt to have friendly faces nearby to ask for a reminder on how to flush a gas manifold, or for borrowing a helium leak detector when ours is on the fritz.

Which goes to say: If you are visiting or working around the Washington, DC National Mall, you could take a walk around for a self-guided exploration of anoxic display enclosures.

Why do we use anoxic displays? To answer this question, it is useful to start with a different question: why do materials discolor in the first place? Many fading or color-change concerns are the result of photo-oxidative chemistry, where light and oxygen combine to cause visible changes in a material. Most of us enjoy the light and oxygen all around us! They are so integral to daily life that it’s easy to forget that light and oxygen are two of the most potent chemical reactants available.

The easiest way to prevent photo-oxidation is to remove one of those reactants: light or oxygen.  There’s a third reactant too. The object on display. But we’d like to keep that one.

A large metal case with attached computers and sensors set up inside an exhibition gallery.
Back of the Waldseemüller encasement with its accompanying sensors and detectors, without the surrounding gallery cabinet. Credit: PRTD.
A group of people stand and point behind a large display case holding a map.
The installation team inspects the back of the Waldseemüller map encasement. Credit: Fenella France, PRTD.

When thinking about exhibiting collection items, we can’t very well remove the lights if we want to see anything. We might dim them or put sensitive objects on display for short periods of time, but we can’t remove lights entirely. So if iconic items are planned to be on illuminated display for a long time, we’re left with one option. Remove the oxygen. To do this, the object is enclosed in a sealed display case, the air inside the case is flushed and replaced with inert and humidified Argon gas, and this atmosphere is hermetically sealed to provide an oxygen-free, air-tight, environment. At the Library, anoxic encasements represent much collaborative work between the conservators and scientists in the Preservation Directorate, as well as the experts at the National Institute for Standards and Technology. Removing oxygen is easier said than done. The sealed display encasements are a work of impressive science and engineering. There is plenty to distract the installation team away from the unique world map in the window.

Most days, however, all of this engineering is tucked away behind the gallery display cabinets, where the inside looks more like this.

A researcher stands in a dark cabinet next to a metal encasement with visible tubes and wires.
Working inside the gallery cabinet around the Waldseemüller encasement. Credit: Andrew Davis, PRTD.

The above images all show the anoxic case currently displaying the 1507 Waldseemüller world map. This map was produced by Martin Waldseemüller, highlighting the recent explorations of Amerigo Vespucci and being noteworthy for its first ever presentation of the separate continents of the western hemisphere and with a new label on them: “America”. The encasement for this map was developed and tested over the course of a few years and installed in the Library’s Jefferson Building in 2007. To date, this encasement at the Library remains the largest anoxic display encasement in the world. You might better appreciate its size and ambition with this picture from when it was installed, showing the encasement being hoisted through a window of the Jefferson Building.

A crane hoists a large wooden box, with workers guiding it through a second floor window between large columns.
The Waldseemüller encasement being hoisted on a crane through a second floor window of the Jefferson Building for its installation. Credit: Dianne van der Reyden, PRTD.

The second low-oxygen encasement currently in use at the Library is exhibiting the Abel Buell’s A New and Correct Map of the United States of North America, the first map of the United States made and published in America by an American. This encasement was installed in 2013 and incorporates some changes from the Waldseemüller map case. One notable difference is that this case’s atmosphere is hypoxic rather anoxic, meaning it is not truly oxygen-free. Rather it has a small concentration of oxygen, approximately 5% oxygen, which is still much less than 21% oxygen in air. This map case holds its desired atmosphere just as well as the Waldseemüller map case, but a small amount of oxygen was intentionally included in its sealed atmosphere. The reason for this was the presence of the pigment Prussian blue, prominently visible on the map’s flag. Prussian blue is one of a few curious pigments with an unusual response to light and oxygen. Unlike most materials where removal of oxygen inhibits discoloration, Prussian blue benefits from the presence of oxygen. The exact mechanism is fairly complex and still a topic of scientific research, but it has been observed that oxygen actually helps Prussian blue revert close to its original color after light exposure. The small amount of oxygen was included in the Abel Buell map case to help keep the map’s flag blue, while still being low enough to preserve the color of other materials on the map

Zoomed region of a map with an illustration of a historic American flag, angelic figures, and text reading “A New and Correct Map of the United States of North America”.
Flag from Abel Buell’s A New and Correct Map of the United States of North America,

Each of these map encasements has its own gas manifold running across their back, where the sealed atmosphere can diffuse to reach a variety of sensors for reading oxygen content, as well as other properties inside the case such as temperature, relative humidity, and pressure relative to outside conditions. This last point is important. Barometric pressure changes all the time, but the gas is only sealed inside the case at one moment in time. As the atmospheric pressure changes with weather, the sealed gas inside the case exerts a relative positive or negative pressure difference. If the pressure changes dramatically, it may be enough to break the display window and cause damage. Fortunately, that has never happened, as the encasements (and our contingency plans in emergencies) were designed with typical DC-area conditions in mind. But we monitor them just in case.

In the years between the two map cases at the Library, the science of encasements did not change much but measurement instrumentation in these sensor manifolds did. The sensors on the Abel Buell encasement, being 6 years newer, integrated much more easily into online access tools than the original equipment on the Waldseemüller encasement. This allows us to easily get live browser-based tracking of the conditions in the case at any moment or previous time period. The Waldseemüller encasement has slowly been upgraded to similar functionality over the past years.

A series of data plots for oxygen, barometric pressure, differential pressure, dew point, relative humidity, and temperature over time.
Screenshot of February 2020 data from the Abel Buell map encasement sensors for various oxygen, pressure, and temperature measurements. Credit: Andrew Davis, PRTD.

These live data readouts are useful in ensuring stability of the encasement. For example, particularly stormy conditions are frequently accompanied by rapid changes in barometric pressure that might wreak havoc on the case integrity and seal. The plots above include a particularly nasty day of storms in February 2020, leading to one of the greatest differential pressure spikes seen between the case and its surrounding environment since its installation. Yet the oxygen reading (top left) remained steady, indicating that a good seal was maintained throughout the storms. This live accessibility provides us preservation peace-of-mind, and easy access to historical data allows us to trace trends and see if conditions (or more likely: sensor calibrations) are drifting. In the years since their installation, these cases continually maintained their desired atmospheres and seals.

Back of a metal encasement with tubing and wires, with a domed ceiling and mural in the background.
Back of the Waldseemüller map encasement in the Jefferson Building’s Pavilion of Art and Science. Credit: PRTD.

I do like to pause at the above picture at the back of the Waldseemüller map case. With the gallery display cabinet usually in place around the encasement, you rarely get to see the combination of the highly engineered encasement for a 16th century map against the backdrop of the Jefferson Building’s domed ceiling in the very appropriately named Pavilion of Art and Science. It is a lovely demonstration of STEAM (Science, Technology, Engineering, Arts, and Math) at the Library.

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Comments (4)

  1. Thank you so much for this very interesting and informative blog! Seeing the backs of the cases is really amazing!

  2. Very informative. Useful for Library docents who introduce the maps to the public. You might share this information with the Visitor Engagement Office. Thanks.

  3. This blog, which ignores a whole herd of elephants in the room, provides a much needed forum to make them visible.

    It has been known since 2014 that iron gall ink is another pigment like Prussian blue for which oxygen “inhibits discoloration” (i.e. light-fading) by reoxidising the photoreduced form of the very similar coordination complexes (Ford 2014). Oxygen is their friend, protecting them from the potential harms of illumination (Townsend et al. 2015). Nevertheless, the LOC, Smithsonian, and NARA (among other US institutions) persist in displaying historic documents containing iron gall ink in NIST anoxic cases containing as little as 0.003% oxygen, including the Charters of Freedom, the Magna Carta and the LOC’s Waldseemüller map referred to in the blog, which contains an inscription written with the ink (Wanser 2003). They cannot have it both ways, the research tells us that what harms one, harms the other and the same precautions must logically be taken for both pigments until and unless research indicates otherwise.

    For decades the same institutions including NIST confidently predicted that anoxia would – as NARA claimed of the current Charters display enclosures – “protect them from photo oxidation, a fancy chemical way of describing light fading” (PBS 2005). This was wrong on both counts, they don’t offer that protection and photooxidation is not synonymous with fading. Furthermore, their theory dictated the cases would be effective only if oxygen levels orders of magnitude lower than the 5% in the Buell map case were maintained indefinitely, conditions which account for most of the exorbitant cost of the NIST cases. The blog is correct to say it isn’t easy or cheap to do so. Since Ford’s paper was published, the Washington cultural institutions have quietly ceased promoting the benefits of anoxia for iron gall ink, however NIST still advertise that “by sealing iron gall ink documents in an anoxic, or nearly oxygen-free environment, the ink’s deterioration can be stabilized” (NIST 2018). They know this is untrue, because a year earlier they said the opposite; stating that 5% oxygen was required for the New York State Education Department’s 1862 draft of Lincoln’s Preliminary Emancipation Proclamation because “the color of the iron gall ink on the document can change very gradually in the absence of oxygen” (NIST 2017).

    The blog fails to mention there is no empirical evidence to support the improbable claim that the same oxygen-rich environment which protects the inks by ensuring their reoxidation, would somehow provide useful protection against the oxidation of the parchments and paper they are written on. Furthermore, it is rewriting history to say the documents’ custodians assumed they would “ALWAYS have light on them”; on the contrary most documents in these cases are frequently or permanently displayed only because of them. For example, on receipt of a NIST case for their copy of the Bill of Rights in 2013, the New York Public Library announced, “a part of the reason why we haven’t displayed it continuously is because the other copies are so faded that you can hardly see any of the words … it was not meant to be out all of the time, but this special encasement will allow it to be” (Pang 2013). In the early 20th Century, the Charters were likewise never displayed because it “would endanger the Declaration of Independence which is badly faded” (NYT 1920), however they have now been on permanent display in their NIST (formerly NBS) anoxic display cases since 1951. The US Government was right to be cautious about the Declaration; NARA has 20-year-old data, never released, which unequivocally demonstrates that the Declaration of Independence is in a state of “severe degradation” because of past display practices and , as a consequence, is highly vulnerable to further degradation (Young 2005). The US government’s current reckless attitude is not universally shared, for example referring to an anoxic display case built for Scotland’s own declaration of independence from England, the Declaration of Arbroath, the Keeper of the Records flatly stated, “regular exhibition of this fragile document will never be possible, but this important project may allow its very occasional display in the future” (BBC 2005).

    The blog incorrectly states that the photoreductive fading of Prussian blue and iron gall ink are unusual. The fact is, photoreduction of dyes has long been recognised as reasonably common, particularly on proteinaceous fibers like wool or silk (e.g. Giles and McKay 1963). More relevantly, the widespread photoreduction of other compounds and complexes containing Fe(II) – which is what Prussian blue and iron gall ink have in common – is an important and well studied natural phenomenon in which the bioavailability of iron as Fe(III) is enhanced by light.

    To add to the institutions’ anxieties, several of the documents displayed in anoxia are on loan from philanthropists like David Rubenstein, some of whom shelled out a fortune for NIST cases to protect them from the consequences of display. In 2013 Ed Wachenheim III donated US$600,000 for NYPL’s Bill of Rights (above) proclaiming “I started thinking…if in the course of the next several years a handful of the millions of people who will see the Bill of Rights can have the idea to advance democracy, to advance human rights in some way, then this very expensive box will turn out to be one of the best investments the New York Public Library has ever made” (Pang 2013). Who wants to tell these gentlemen, whose largess institutions like the Smithsonian rely on, that anoxia cannot protect iron gall ink from light-fading, and that – even assuming an atmosphere of 5% oxygen is someday proven to provide marginal protection to paper and parchment – it could just as well be maintained inside a Tupperware cake box? At best these boondoggles are a waste of money, at worst positively harmful.

    (source links removed).

    BBC (British Broadcasting Corporation). 2005. “Public to See Arbroath Document”. April 1.

    Ford, Bruce. 2014. “The Accelerated Light Fading of Iron Gall Inks in Air, Hypoxia and Near-Anoxia.” In ICOM Committee for Conservation preprints. 16th Triennial Meeting, Lisbon. Paris: ICOM. 15-19.

    Giles, Charles H., and Robert B. McKay. 1963. “The Lightfastness of Dyes: a Review.” Textile Research Journal 33 (7): 528-577.

    NYT (New York Times). 1920. “50,000,000 to View the Constitution …. Opened at Rare Intervals.” January 18

    Pang, Amelia. 2013. “Original Bill of Rights Made Public to Give Hope to the World.” Accessed 19th August, 2016. Epoch Times.

    Townsend, Joyce H., Jacob Thomas, Stephen Hackney, and Andrew Lerwill. 2008. “The Benefits and Risks of Anoxic Display for Colorants.” Studies in Conservation 53 (sup1): 76-81.

    PBS (Public Broadcasting Service) 2005. “Saving The National Treasures.” Accessed October 3, 2021.

    Wanser, Heather. 2003. “Treatment and Preparation of Waldseemüller’s Map.” Library of Congress Information Bulletin 62 (9).

    Young, Gregory. 2005. “Preservation Assessment Charters of Freedom of the United States of America.” Unpublished Canadian Conservation Institute Report No. Proteus 79696, Ottawa, Canada.

    • Thank you for the thoughtful comments. This is clearly a complex topic that involves parties with many varied interests and backgrounds (as you note), and we would enjoy the possibility of a future venue that could better suit discussion of these issues.

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