Treating the Brooklyn Bridge Drawings, Phase One

On January 17, 2020, we introduced the Municipal Archives Conservation Unit’s latest project, “Conserving Central Park and Brooklyn Bridge Plans.” Before the Archives temporarily closed in mid-March, project conservators had devised some innovative protocols for treating the oversized plans (up to 36’ in length!) in these two iconic collections.  

The project is funded by the New York State Library’s Conservation/Preservation Program. The goal is to perform the necessary treatments so that the drawings can be stabilized for improved storage, either rolled, or housed in new 7-foot long flat file drawers.

Conservator Clare Manias examines a 14-ft. Brooklyn Bridge drawing. NYC Municipal Archives.

Project conservators began with the oversize Brooklyn Bridge items. Drawings this large present a unique set of challenges. Routine treatments, transporting the drawings, photographic documentation, and use of available workspace all need to be approached differently. It became clear that we would need to think creatively to make the most efficient use of our time and workspace.

The constraints imposed by the size of the drawings means something as trivial as moving a drawing to the conservation laboratory requires three people. One person opens the doors and ensures the hallway is clear. The other two conservators load the drawings—usually 3 or 4 at a time—on a rigid foam core board which is carried by hand to the laboratory. The size of these drawings and the fact that they are currently housed in Mylar sleeves also makes them very heavy! In the laboratory they are placed on an extra-long table that can accommodate two drawings side by side. Two smaller tables that are on castors can also be pushed together to create another long table to accommodate some of the smaller drawings.

With these constraints in mind, we decided to batch our documentation photography, surface cleaning, and media testing as a “phase one” in treating the drawings. The basic “batch” process is as follows: we photograph a drawing, then while it is still in place on the table, we surface clean it, and test the solubility of the media. We also take notes on the condition of the drawing. Combining these tasks limits how often we need to transport the drawings to and from storage.

It is important to document the process of conservation treatments. Ethically, it is necessary for conservators to leave written and photographic documentation of the treatment that has been performed as a reference for future conservators. The photographic images taken during this process may be the only way for patrons to view the drawings, given their size and fragile state.

The size of these drawings required us to adopt innovative methods for the photography part of the project. Ordinarily, for small objects, a handheld camera or a camera on a copy-stand would suffice; however, these drawings are too long for that method. The majority of the drawings range between 6-to 15-feet in length and are about 2-to 3-feet wide. It is just not possible to capture the entirety of the drawing in one image, thus we shoot the recto and verso of each drawing in sections and later merge them together in Photoshop to create a panorama of the entire work. To successfully do this, we need to make sure that the images are all taken from the same angle, with the same settings, so that they will seamlessly align.

Conservator Sara Bone photographs an oversize Brooklyn Bridge drawing with the camera on the mono-stand, LED lights, and light reflection board. NYC Municipal Archives

The key piece of equipment for this type of photography is the mono-stand. The mono-stand allows the camera to be positioned about 9 feet above the floor, and the height can be adjusted, as needed.  It is also on wheels, so it can easily be moved along each section as we take pictures. Blotters covering the table surface provide a clean, consistent background for the image and help to maintain contrast against the items we are photographing. The height of the camera on the mono-stand is adjusted based on the width of the drawing. A drawing with a smaller width means the camera can be closer to the object to have it fill out the frame.  It is generally best to have the camera slightly zoomed in because when it is fully zoomed out it has a tendency to give a “fish-eye” effect, which makes stitching together the panorama more difficult.

With the camera positioned high up on the mono-stand, we need a stepladder to reach the shutter button! While there are some systems that sync the camera to a computer to remotely release the shutter, this is not possible with our setup.

Another vital piece of equipment are LED lights with softboxes that provide consistent diffuse light to ensure that the images are as accurate as possible. The overhead lights are turned off during photography because they have a warmer temperature light and do not provide even lighting. We rely primarily on the LED lights, although there is natural light that comes through the windows as well. A color bar is inserted into each of the photos so that in post-processing we can adjust the white balance and make sure the color information conveyed is accurate.

Because the drawings are placed on a table and the lights can only be positioned on one side of the table, the top edge of the drawings appear more in shadow. To aid in the way light reaches all areas of the image, we created our own light reflection board. A sheet of blotter was mounted to a rigid board and propped up on stands. When placed on the other side of the drawing on the table, this allows the light to bounce off the white blotter and reflect back onto the drawing. We move the light apparatus along with the mono-stand as we take the photographs at regular intervals, capturing every section of the drawings. Two people position the lights and reflection board while a third person is up on the stepladder taking the picture. Usually all three pairs of hands are needed to carefully flip the drawing over so the other side can be photographed.

In Photoshop, the images are adjusted for white balance and then cropped close to the borders of the drawing. The “Automate: Photomerge” function is used to automatically align the images into a panorama. Manual adjustments can then be made as needed.

Brooklyn Bridge drawing 4121-G, section. NYC Municipal Archives.

Following photography, with the drawing still out on the table, we begin the surface cleaning of both sides, using a soot sponge. The sponge lifts up the surface dirt without being too abrasive on the paper. Many drawings are so dirty that we see a dramatic difference as we clean! After surface cleaning the media is tested to see if it is water-soluble. Testing media is an important step because we need to check whether the ink is stable. We would like to wash as many of the drawings as possible to remove acids and other harmful byproducts in the paper. To test the inks and other media, we drop a small bead of water on an obscure section of the media to see whether the ink will bleed or if any lifts off when pressed with blotter.

Finally, we take notes on the condition of the drawing which completes phase one of treatment. Each drawing is then wrapped in acid-free buffered tissue and moved to temporary storage to await phase two, which will include more targeted treatments such as washing, mending, and lining. Using our batch treatment protocol we will photograph, surface clean, and media test the 78 Brooklyn Bridge drawings in an organized and efficient way.

We are looking forward to resuming the oversize drawings conservation project when the Archives re-opens. Look for updates in future blogs.

Conserving Central Park and Brooklyn Bridge Plans

The New York State Library recently awarded a grant to the Municipal Archives Conservation Unit to perform much needed treatments on large-scale drawings and plans for Central Park and the Brooklyn Bridge.

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Brooklyn Approach, East River Bridge, 1892. Wilhelm Hildenbrand, Brooklyn Bridge Collection, NYC Municipal Archives.

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Lindsey Hobbs pasting out a sheet of Japanese tissue with wheat paste for lining a Brooklyn Bridge drawing.

These two icons of New York are among the most important public works achievements in the city’s history. Beyond the technological and design innovations, the bridge and park have become symbols of the city itself. The more than 200 drawings that are the subject of the grant exhibit the remarkable level of detail and artistry that went into the planning and construction of each structure.

The project focuses on the largest items in each collection, some of which are 34 feet long! Conservation staff are undertaking a variety of activities to assess and stabilize these delicate materials.  These include mending and lining fragile drawings, stabilizing media, washing to remove harmful degradation products, reducing stains from mold and other sources on some of the most important drawings, as well as creating new housings for long-term storage.

The grant funding also supported the purchase of a Zeiss stereo microscope with a digital camera, and portable UV lights. This equipment allows conservation staff to analyze drawing media and supports, assess mold and other types of damage, and take high quality images of fine details, all of which will inform the treatment methods chosen. Additionally, the lab was able to purchase a large mono-stand for photographing oversized collections, both for documentation of the treatments performed as well as to provide another source of research access to these large, unwieldy objects.

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Clare Manias and Sara Bone surface cleaning a Brooklyn Bridge drawing.

The Brooklyn Bridge and Central Park plans comprise some of the most treasured collections at the Archives. Dating from 1850 to 1934, the Central Park plans provide complete documentation during the critical stage of the park’s design and construction from 1850 to 1880. The collection includes renderings of everything from landmark structures like the Boathouse, Belvedere Castle, and Sheepfold to a three-level circulation pattern for people, horses, and vehicles.  The oversized drawings included in the grant project detail the design of the Metropolitan Museum of Art and the Museum of Natural History, gates and entrances to the park, paths and walkways, drainage systems, and other elaborate details.

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Conservators Clare Manias and Sara Bone prepare to photograph a Brooklyn Bridge drawing.

The Brooklyn Bridge collection documents the original construction and subsequent alterations of the 1,596-foot steel suspension bridge connecting Manhattan to Brooklyn. At the time of its completion in 1883, the bridge was the longest in the world and was an important technological achievement. The total 8,706 drawings in the Bridge collection span from 1867 to 1938.  They were produced by architects and engineers who developed techniques for bridge construction that were unknown or considered unproven among their profession at that time. Many of the drawings in the collection are the work of the most celebrated American engineers and architects of the nineteenth century, such as John and Washington Roebling, George McNulty, and Wilhelm Hildebrand. The largest of these drawings is over 34 feet in length.

The drawings and plans in both the Central Park and Brooklyn Bridge collections have similar characteristics. They represent a variety of media (watercolor, graphite, inks, crayon, and photo-reproductive processes) and supports (tracing paper, watercolor paper, cloth-lined paper, and tracing cloth).  Unfortunately, improper storage and handling over the decades prior to acquisition by the Archives has led to physical damage to varying degrees in the form of acidic and deteriorated supports, flaking media, iron gall ink damage, and tears and fractures.

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Clare Manias and Sara Bone photographing a Brooklyn Bridge drawings in sections.

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Assistant Architect Wilhelm Hildenbrand included some delightful details in his 1877 plans for the Brooklyn Bridge. Conservation staff spotted these two almost microscopic figures enjoying themselves on the bridge. A gentleman in a top hat appears to be serenading a lady holding a parasol.

One of the greatest challenges of treating these materials is simply moving them back and forth from and within the lab. Conservators Sara Bone, Clare Manias, and I have developed a workflow for carefully shifting and transporting the drawings using light, but sturdy, foam board to support their weight. We have also refined methods for photographing, cleaning, and performing various treatments on a much larger scale than we are generally accustomed to. Planning each move in advance, and of course teamwork, are key to safely maneuvering these massive and very delicate drawings.

The ultimate goal, as with most of the work we do in Conservation, is to make the oversized drawings safer to handle, more accessible to researchers and well-preserved for the future. As the project moves forward in the coming months, we will continue to learn a great deal about the collections and further refine our treatment methods. Given the many thousands of oversized maps and drawings in the Archives’ collections, these skills will no doubt be put to use again once this project is completed. Although challenging, the work will ensure the viability of these iconic materials for many generations to come.

Iron Gall Ink

Archivists and conservators at the Municipal Archives face many challenges in their work to preserve and provide access to the City’s historical records. This week’s blog discusses the effects of the iron gall ink used to create some of the earliest documents in the Archives collection.

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Example of "burn through" in an untreated page with iron gall ink.

Iron gall ink was the ink of choice in the Western world for well over a millennium. Its indelibility and rich dark tone were desirable traits for artists, scribes, letter-writers, bookkeepers, i.e. virtually anyone documenting something on paper. While other types of inks were also available, such as carbon black and lamp-black ink, iron gall made up a significant proportion of the inks used up to the early 19th century, tapering off rapidly after that time. Iron gall ink, however, also has the unfortunate trait of damaging the paper it is written on. Over time and depending on certain conditions, the ink can fade to a light brown, create a haloing effect around letters, or “sink” through the paper. The ink in extreme cases will corrode the paper support, leaving areas of losses resembling burn marks in the paper. The effects can be seen in drawings by Leonardo Da Vinci, early drafts of the U.S. Constitution, and manuscripts of Victor Hugo, to name a few. The ink poses a formidable challenge for institutions with pre-19th-century manuscripts in their collections, including the Municipal Archives.

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Oak galls.

The effects of iron gall ink have long been known to conservators but are still not fully understood. The ink is composed of four main ingredients: tannins, which come from oak galls—a growth triggered by parasitic insects that attack oak trees; iron sulfate in the form of bluish-green salt crystals; a binder, usually gum arabic from the acacia tree, added to improve the flow of the ink; and lastly, water or wine. The ink achieves its rich bluish tone after the solution is exposed to air while writing.

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Iron sulfate

Research has shown that the two main ingredients in the ink, iron salts and tannic acid, each pose separate risks to paper, risks that are exacerbated by certain environmental conditions. The concentrations of the ingredients, the preparation method, the presence of other contaminates in the ink such as copper or zinc, the amount of ink that is absorbed into the paper, and even the type of writing instrument used, all influence and further complicate the degradation process. As a result documents that are produced at roughly the same time may exhibit a wide range of condition levels.

This variability is easily seen in the pages of manuscripts in which one page appears stable, while the adjacent page may show signs of severe degradation. In these cases it’s possible that the writer used a new batch of ink on the adjacent page or a new writing instrument, or even perhaps a new writer with a much heavier hand stepped in on the following page. It’s often impossible to say. These numerous factors, of course, complicate the role of the conservator, who must determine the best approach to treating and preserving collections.

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Book of 17th-century land conveyance records showing the variability in condition of different pages. NYC Municipal Archives Collections.

In some of the Archives’ original Dutch and English records, which document the founding of New York City by Dutch colonialists in the mid-17th century and the subsequent English takeover, the wide-ranging effects of iron gall ink are on full display. Some of the Dutch records were treated by Archives conservators in the late 1980s by a process called leaf casting. The treatment involves filling in losses on a damaged sheet via a water bath with new paper pulp. The water is slowly pumped out, allowing the pulp to fill in any missing gaps in the original document and create a more stable structure. The treatment also washes away water soluble iron II ions and acidic elements in the paper that contribute to its deterioration.

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Dutch records that were treated by leaf casting in the 1980s. NYC Municipal Archives Collections.

The documents that underwent this treatment more than 30 years ago are in markedly better condition today than those that have undergone no treatment. While leaf casting does not address the full range of issues that iron gall ink brings—a near impossible task for conservators racing against time and often less than ideal storage conditions—it has certainly proven to have been a worthwhile approach that likely prevented significant future losses.

The treatments available for collections with iron gall ink continue to evolve, as more research is conducted. And, additional options have been developed since these collections were treated years ago, such as a calcium phytate/calcium bicarbonate treatment. Municipal Archives conservators will continue to monitor the remedies for these important materials.