Catarina and I are working on rehousing a large series of College of Engineering class composites from the mid-1950s through the early 2000s. It is a fantastic visual timeline of 20th century photographic processes. It also perfectly charts cultural shifts through the decades (so many haircuts and mustaches!) There was even a gentleman that I sang in Chorus with during my years as a student here! But even beyond all of that, there were some unexpected tiny bits of Cincinnati history. The University handles its own photography now, but that wasn’t always the case. The early class composites were done by local businesses. The bulk of them were done by three now-defunct studios: Pogue, Shillito’s, and Rob Paris Photography. If you are a Cincinnati native, you may have heard of them. If you are of a certain age, you may even have had your portraits done by one or all of them. (I personally had portraits taken at Shillito’s as a child.) What a fun little piece of history. Of all the things that I enjoy about working with the photographs in our collections, I think the unexpected finds may be my favorite!
Hyacinth Tucker —- (UCL) Conservation Technician and Bindery Coordinator
As conservation professionals at the Preservation Lab, we get to see and work with our fair share of historic, rare, and just plain interesting artifacts. I recently had the pleasure of becoming familiar with an item that is all 3 of these, and just so happens to be one of The Cincinnati & Hamilton County Public Library’s (CHPL) most prized possessions: the Fontayne and Porter 1848 Cincinnati Panorama Daguerreotype.
Cincinnati Daguerreotype Panorama by C. Fontayne and W. Porter, 1848
For those who are unfamiliar, a daguerreotype is the very first photographic process, utilizing iodine-sensitized silver plates and mercury vapors, often offering stunning detail and resolution. Currently on display in the downtown Main Library’s Cincinnati Room, the Cincinnati Panorama is no exception, and is considered one of the most detailed and vivid examples of daguerreotype photography currently in existence.
Daguerreotype photography is not without its challenges, however. Most significant of these (at least which concerns us in the conservation field) is that daguerreotypes are extremely delicate. They scratch easily and can degrade with simple exposure to oxygen, atmospheric pollutants, and moisture. These attributes bring up a difficult question: how does one display an item like this, while also ensuring its preservation for generations to come?
Enter Ralph Wiegandt. Wiegandt is a Photograph Research Conservator who designed and installed the 1848 Cincinnati Panorama’s enclosure and display case in 2008. He routinely has performed on-site follow-up consultations in 2012, ’14, ’16, and most recently this past June with Genealogy and Local History and Preservation Lab staff. My fellow lab mate, Hyacinth, and I had the good fortune to also meet with Wiegandt on this recent visit to attend a presentation on his uniquely designed enclosure. Although the primary purpose of the visit was to discuss the enclosure, Ralph shared no shortage of information about daguerreotype plates, the photographers (Fontayne and Porter), the conditions surrounding the panorama, and much more.
Ralph Wiegandt, photo by Hyacinth Tucker
It was clear from speaking with Wiegandt that this project was one he was deeply passionate about, referring to it as “a seminal object in my career.” He spoke with excitement about the unique attributes the Cincinnati Panorama showcases, chief among them: the stunning detail and clarity. According to Wiegandt, this image is so detailed that it can be magnified up to 30x before experiencing any resolution loss. This allowed for intense digital imaging to be performed during the initial conservation of the daguerreotype in 2008. In this process, digital photos were taken from different degrees of closeness to the original image and then stitched together, creating one large interactive digital display, viewable here.
Wiegandt informed us that the 1848 Cincinnati Panorama was not the first attempt at such a picture. Just several months prior, W.S. Porter had taken another daguerreotype panorama of the Fairmount Water Works in Philadelphia.
Fairmount Water Works Daguerreotype Panorama by W.S. Porter, 1848
The detail of this image, however, is not as impressive as the Cincinnati Panorama. What can be gleaned from this fact, according to Wiegandt, is that the Philadelphia capture was a successful learning experience for Porter, and that his skills and techniques were able to improve dramatically by the time he attempted the Cincinnati Panorama with C. Fontayne.
At the time of the Cincinnati Panorama, daguerreotype photography had only existed for 9 years. Equally as remarkable as the detail these images were able to capture is the inception of this technology. Wiegandt explained how Louis-Jacques-Mande Daguerre experimented with plates of silver sensitized with iodine fumes. The idea was that the sensitized silver would be reduced as it was exposed to light (i.e., the shutters on a camera opening and allowing light from the image field to hit the plates), thus creating latent images in the silver. Although this proved to be successful, a viewable image was not detectable until a chance happening, which Wiegandt describes as “a miracle.” Legend has it that one of Daguerre’s exposed plates was stored in a cabinet, sharing this space with one other singular item: a broken instrument that utilizes mercury (such as a thermometer, barometer, etc.). Upon examining this plate, Daguerre realized the latent image was now detectable, correctly deducing that the mercury fumes had developed the film. The fumes had caused the light-exposed areas on the silver plate to form small bumps, roughly 1 micron in size, creating an instant high-resolution image. The microscopic size of these bumps means that, according to Wiegandt, daguerreotype images are an early example of what we would today call nanotechnology. (Ralph also notes the actual circumstances of its discovery are unclear since any notes from Daguerre’s studio would have been lost during a fire shortly afterwards.)
Much like the Fontayne and Porter Cincinnati Daguerreotype, the current display case is quite unique as well. As mentioned before, daguerreotypes are incredibly delicate. To successfully prevent further degradation and preserve this object for generations to come, its exposure to oxygen and other reactive gases must be severely limited. The solution that Wiegandt produced was a specialized inert gas case, similar in concept to how the Declaration of Independence is housed. The goal of this case is “to maintain a slightly elevated pressure of a non-reactive gas such that it will not put excessive strain on the seals yet will be above the potentially highest barometric pressure” (Wiegandt, 2006), thus preventing any atmospheric air from coming in contact with the sensitive daguerreotype plates.
Wiegandt’s sealed encasement design sketch provided in treatment documentation
Wiegandt chose argon to pressurize the case with as it has a better diffusion rate and is more inert than other gases such as nitrogen, all while being cost effective.
Wiegandt informed us on his most recent visit that the case is doing its job: the panorama has experienced no detectable degradation since its installation. However, this was likely his final visit to the Cincinnati Library, as he is retiring from the field. I should add that a further and perhaps more important purpose for this visit was to advise and inform CHPL (and Preservation Lab) staff to be successful in monitoring and caring for the object in his absence. Fortunately, Wiegandt was able to leave us with a wealth of information and resources that will aid in the continued preservation of this amazing artifact. With an updated preservation plan, knowledgeable staff in both the Genealogy & Local History and Preservation Lab departments, and a commitment to preserving cultural property, we can be confident the Cincinnati daguerreotype panorama will be enjoyed by library visitors for many generations to come.
This past March, at one of our Special collections meetings, the Lab received a photographic project from UC’s Classics Library. This was a large German collection comprised of 16 series, each series with approximately 300 photographs, a total of about 4800 photographs!! These are silver gelatin photographs that depict ancient sculptures. The photographs are important since in some cases they show sculptures that may have been destroyed during the WWII.
All the photographs were curled, some showed silver mirroring, and minor tears along the edges, or creases. Most of the conservation treatment focuses on humidification and flattening of each photograph. With such a large number of photographs, the project was divided between Chris (Senior Conservation Technician), Hyacinth (Conservation Technician), and myself (Assistant Conservator).
We each took a series of photographs to work on. Ahead of starting the project, we conducted some tests, along with Ashleigh (Conservator), to understand how long we should humidify the photographs, we create the pressing stacks that would be used for the flattening, and some guidelines that we could all refer to throughout the projects.
We concluded that we would obtain the best results by only humidifying the photographs for a maximum of 20-30 mins and then pressing them. First, we pressed the photographs between pressing stacks of thin Hollytex, blotter, Rising Museum Photomount mat board and binders board for two days. Then we pressed them in a book press or under weights between Photomount mat board until the compression enclosure is created. Before humidification, each photograph was surface cleaned with a hydrophilic sponges.
During Treatment – Small batch of Photographs being humidified in a cold humidity chamber.
During Treatment – Photographs being prepared for flattening by being pressed in a pressing stack.
After being humidified, small cracks on the emulsion and small tears were repaired.
Chris is usually faster with any treatment, so his batch has been fully treated, and now he is in the process of making an enclosure, a cloth clamshell compression enclosure to ensure the photographs don’t start to curl again.
During Treatment – Chris working on the cloth clamshell compression enclosure.
I am still working on my batch. I currently have one-fifth of the photographs being pressed and the rest are awaiting humidification and flattening. This is a long project that requires constant monitoring and time for pressing, but it is so satisfying to see the photographs slowly relaxing and flattening. It will probably take us a few years or more to fully complete the entire 16 series, but once the project is complete each series will be safely housed and repair.
Before Treatment – Photographs as they were received in the Preservation Lab. Overall, curled with small tears along the edges.After treatment – Photographs have been humidified and flattened, each received minor stabilization treatment After treatment – Photographs flattened.
John Robinson’s circus was a famous, traveling, family-owned circus’ that toured the United States for 69 years beginning in 1842. The family business stopped touring around 1910 and was officially sold in 1916. It was managed by four generations, all named John Robinson.
As a local tidbit to note, the circus was stationed during the winters near Cincinnati, OH, where the family owners kept Tillie, the beloved elephant. Tillie was said to roam the neighborhood of Terrace Park and was well known in the community and beyond. Many stories were written of heroic accounts and even her ability to “talk”. She was memorialized when she passed in 1932 and a marker can be found at Circus Place in Terrace Park today.
Elephants being forced to perform in John Robinson’s 10 Big Shows. Image from the Cincinnati and Hamilton County Public Library
Cincinnati and Hamilton County Photographic Album
A rare photographic album owned by the Cincinnati and Hamilton County Public Library (CHPL) dates to the late 19th to early 20th century and contains albumen portraits of John Robinson’s circus performers. The images have been fully digitized after receiving treatment to improve legibility at the Preservation Lab. The CHPL Digital Library catalog describes the object as follows:
“Album of 266 photographs of varying sizes. Most are portraits of Robinson family members and of the circus staff and performers. Included are group portraits of the work crew, musicians, clowns, acrobats, novelty acts, and family acts, and circus animals. Many of the individual portraits are of side-show performers such as tattooed men, albinos, women with floor-length hair, dwarfs, etc. Some of these are studio shots that may have been sold or used as advertising. A small number have captions, and the few with dates are from 1901-1909.”
Inside of upper cover after treatment
Toned Images
While the content of the images is spellbinding, the album is also unique as many of the photographs appear to be once toned overall with pink, yellow, or orange colors.
An online reference from the American Institute for Conservation (AIC) Preprints in 1980 refers to historic albumen photographs that were dyed and are extremely light sensitive. In the article, James Reilly states, “A great deal of the paper sold during the 1880’s and 1890’s was “doubly albumenized”, i.e., floated twice to obtain maximum gloss. Another common practice was the addition of aniline dyes to the albumen solution. Tinted paper was mainly used for portraits, and the most popular tint appeared to be pink, but various shades of purple, blue and even green were also used. Because the dyes had such poor lightfastness–especially in such dilute solution–most of the dyed paper is difficult to recognize today.” It’s fun to imagine that these tinted papers might have been used to capture and celebrate the lives of circus performers in John Robinson’s 10 big shows.
Many of the colors in the photograph album have faded irregularly, with the pink being the most prominent color remaining. This colored photograph phenomenon does not appear to be widely documented elsewhere as the fugitive dyes were not light-fast. They may have also been susceptible to dark fading and chemical instability. Because these photos were preserved within pages in an album, it’s possible they’ve been protected from light and some of the more chemically stable images have not yet completely faded, allowing us a glimpse of this rare format.
While treatment cannot be performed to recolor the images, some photographs did receive conservation treatment to improve visual legibility. There were nearly 30 images that appeared to have a dark discoloration. These photographs were identified to be missing fragments of paper backings. As a result, the dark album pages behind the photographs were obscuring the visibility of the photographic emulsion layer. Some of the more badly damaged images were carefully lifted, relined and reattached. Others received general surface cleaning. A few examples of improved readability are below.
Ashleigh Ferguson Schieszer (CHPL) – Special Collections Conservator
The Preservation Lab has enjoyed our involvement in the Vesalius lecture series and exhibits including preparing the loan agreements, leading and assisting with photographic documentation, and providing spectral and computational imaging to the Vesalius researchers and lecturers.
Some of this work made a guest appearance on the FoxNews 19 segment, starring Dr. Stephen Joffe, on the three rare books that had been on view in December in the Winkler Center.
To celebrate nationalPreservation Week (April 25 – May1, 2021), staff at the Preservation Lab are sharing the following answers to the question below as they reflect upon the wealth of library resources located in the Cincinnati community:
What is your favorite treatment or project that you have worked on in the Lab?
Jessica Ebert:
Learning a new photographic imaging technique, RTI
In April of 2017 I had the amazing opportunity of attending a 4-day workshop at Yale University to learn Reflectance Transformation Imaging (RTI) from the experts at Cultural Heritage Imaging. It was one of the most exciting experiences of my career, and when I came back to the Lab to show the staff what I had learned, Aller Bucher Und Schrifften volume from Martin Luther was one of the first items we captured with RTI. I remember that moment when Catarina and I completed the capture and processed the images – we were just in awe of everything we could see with RTI that we couldn’t under normal illumination. Since then, we’ve made changes to our equipment and our workflow, so now the results are even better than they were back then…but this will always be my favorite.
The left side of the image shows the front cover under normal illumination, or what you see with your naked eye, whereas the right side is a RTI generated image using the specular enhancement mode.
This generated snapshot illustrates the Static Multi Light mode. Below the center panel that features a portrait of Martin Luther you can see “1571”, and above the panel you can see “ID”, both of which are virtually impossible to see in the normal illumination image.
Of all the projects I have worked on at the Preservation Lab, this item is by far one of my ultimate favorite treatments I was able to perform. This book was brought to the Preservation Lab in poor condition. The book had no binding, the text block was split in multiple areas, the sewing was broken, and several pages of the text block where either torn or had extensive loss. In addition, most of the text block showed signs of water damage. Since this book was in such poor condition and the curator of the collection wanted the book to be handled by scholars and the public, it was necessary to do a full conservation treatment.
I was thrilled when I got assigned to this book treatment. I love to work on any book, but the more complicated or involved treatments the better and this was definitely the case. In this treatment, I was able to repair the text block, reduce some of the tideline staining, fill losses and resew the entire text block, while also creating a new binding (called a split board binding) that is strong and flexible to allow such a heavy book to be read.
Before Treatment – Initial condition of the book when it was received by the Preservation Lab. The text block was split, the sewing was broken, and several pages were torn or had paper loss.
After Treatment – Conservation treatment complete. After the text block was repaired and resewn, the book received a new split board binding that allowed the heavy book to be read while mitigating further damage.
After Treatment – The new split board binding provided the book a more flexible opening.
This treatment took a long time to complete, and to this day it is still one of the projects that I have enjoyed the most. Click here to see the complete treatment report and all the photographic documentation. To learn more about conservation split board bindings, check out the Preservation Lab blog post by Kasie and Jessica.
Kasie Janssen:
Iron gall ink treatment of the CHPL Jones Account Book
Washing and rebinding treatments are always a favorite when they come across my bench, as they allow a highly damaged item to become usable and accessible once again. An account book of Jones and Rammelsberg offered one such treatment as it came to the lab with a myriad of issues: a damaged book block without a binding, corroding iron gall ink, previous mold damage, and a shocking amount of pest evidence. The treatment is incredibly memorable because to tackle the issues of aging iron gall ink I was able wash the pages of the book block using a calcium phytate bath to stabilize the manuscript. Once the washing was complete, I was able to resew and rebind the book block, making it whole, functional, and protected once again. It is rare and special to have done such an involved treatment, but in this case the in-depth steps allowed previous damage to be treated and helped remedy the inherent vice of aging materials.
The book block before treatment was highly damaged, so much so, that it was difficult for library patrons and staff to access and use the item without a cover.
Handling the book, you’d never know the hours of labor that went into the treatment (including learning!), but its functional form makes it ready for use once again.
Creating the Italian ledger binding for our teaching model collection
The lab creates a lot of models. Many of these models are made in preparation for treatments. However, some models are created with instruction or engagement in mind. These models, such as the Italian stationery binding (laminated archival bind) I created, help illustrate the history of the book as its form and manufacturing process change over time. Check out the model at the blog entry where you can see a video of the binding being handled. Follow the instructions on the blog make you very own, and in the future, come see it for yourself when our in-person open houses resume in the future.
View of the cover fully opened that shows the overband lacing pattern, the front fore edge flap, and the buckle clasp.
Ashleigh Ferguson Schieszer:
Treatment of a Haggadahowned by Hebrew Union College
I particularly enjoy the problem solving nature of special collection treatments and thus, my “favorite” treatment is usually the one I’m working on. Currently, I’m treating a Haggadah owned by Hebrew Union College that dates to 1526 or 1527. While I’ve treated other haggadahs from HUC, including this one, this project involved iron gall ink treatment AND rebinding a textblock with two different sized leaves, or pages, into its original historic leather cover. Because the binding had been previously treated and reformatted with materials that did not age well, collaboration with the librarians at HUC required exploration into whether we wanted to re-create the past reformatting option with longer lasting materials, or perhaps, explore a new option altogether. Before we committed to a solution, I created a model to test out a new option since unanticipated questions or outcomes often arise during experimental pursuits. For that reason, it’s better to problem solve on a model, rather than on an actual special collection material. In the end, the librarians and I were happy with the results of the new option, and I’m currently at the stage where I’m ready to start rebinding the pages of the actual object.
The top image shows the book open to smaller sized printed leaves before treatment. Leaves are previously reformatted with yellowed tape along the edges, attached to larger paper frames. Paper frames are cockled and distorted. The middle image shows a detail of untrimmed, full-size manuscript leaves. The bottom image shows the fore edge of the binding before treatment.
These images show the model that explores a solution to encapsulate the smaller pages into polyester sleeves that could be sewn into the binding next to the larger pages. This required staff to weld polyester sleeves with paper hinges that could be sewn through like a gathering.
The image shows the binding ready for resewing with its new encapsulated leaves, or pages, next to the created model.
Not only was this piece based on a favorite subject of mine (I love Shakespeare!), this was a historic photograph treatment I was able to handle with just a little guidance. I was able to properly identify the photographic elements on the first try, performed a surface cleaning on the piece, and created my very first cloth-covered clamshell and cradle to house it. It was such a wealth of learning experiences within one project, which is the best part of my work!
Before cleaning; albumen card (note the finger prints in the upper right corner). The image depicts the photographer as a soldier.
Cloth-covered clamshell exterior.
Cloth-covered clamshell interior, with piece opened to surface cleaned soldier image in integrated cradle.
Chris Voynovich:
Constructing a custom cloth-covered enclosure to house the Public Library’s William S. Porter Collection of photographs
One of my favorite aspects of the job here, in the lab, is designing and creating custom enclosures. This collection of rare daguerreotypes, ambrotypes, and tintypes is an example of adapting a standard cloth covered clamshell to accommodate a collection. I created two trays with pull tabs that are removable for easy access and display. Each photograph has its own tuxedo box and is set in polyethylene foam (Volara) for protection. The tuxedo box enclosures are identical in size to reduce confusion while repacking. Check out this blog created by Jessica that shows a gif of the enclosure opening and closing, and this blog post showing a similar enclosure I created for a dairy collection.
View of the opened cloth-covered clamshell with the two removeable trays in place. The trays contain the collection of cased photographs in tuxedo boxes with labels for easy identification.
This image shows the bottom tray partially pulled out, displaying the two larger cased photographs.
Today at 3pm (EST) join Jessica and Catarina on the Preservation Lab’s Instagram (@thepreservationlab) for a quick, informal Instagram Live.
Then tomorrow, make sure to tune into the Public Library’s Instagram (@cincylibrary) at 12pm (EST) for an in-depth Instagram Live event where Catarina and Jessica will be sharing treatments they are currently working on; giving you a behind-the-scenes look and answering all your questions “Live in the Lab”.
Previously, we talked just a little bit about halides, and how they fit into the formation of silver gelatin-based images. Today, we’re going to take a closer look at part of the “how.”
Let’s begin with a brief overview of the darkroom process. As a reminder, the mechanics of creating a black and white print generally include the following steps:
A paper is pre-coated with a halide salt and silver nitrate that are mixed in a binder such as gelatin.
An image is first generated by projecting a source of illumination (like the sun or a lamp) through film onto a coated piece of paper.
Next, the paper or film is developed in a bath of chemicals. This is the part of the process the image seems to “magically” appear!
The image developing chemical reaction is stopped in a “stop bath.”
The paper or film is moved to a second bath to “fix” the image in a fixative bath.
The photograph is rinsed and hung to dry – ready to safely see the light of day.
Now, let’s delve a little deeper into the chemical reaction described in step two, beginning with a bit of a thought experiment. If I say to you, “semiconductor,” what springs to mind? Something involving electronics, perhaps? Maybe chips, lots of little circuits and tiny wires? Maybe, if you’re more photography-minded, a digital camera? All excellent things to think of! With this in mind, what if I told you that our silver gelatin emulsion is also a semiconductor, one that converts light into latent images instead of electricity?
Well, that is what we’re going to explore today, the basics of the mechanism by which light gets our emulsion ready to record latent images. The light shines on an atom (in this case, our silver halide ion), energy is transferred to an electron, and the electron moves to an excited state and is ready to make chemical magic.
If you refer back to your basic chemistry, atoms are composed of three parts: protons, neutrons, and electrons. Protons are positively charged and reside in the nucleus (center) of an atom with chargeless neutrons. Negatively charged electrons orbit the nucleus in bands. When all things are equal, an atom has the same number of protons as electrons, leaving the atom neutral. There aren’t a lot of atoms that are naturally like this, however; an atom will often have too many or too few electrons in orbit. This is a good thing, as it not only makes them stable, it makes them available for bonding with other atoms and creating chemical reactions.
Now let’s apply some of that to our silver halide. The electrons near the nucleus of our ion are in the “ground” state. They’re unexcited. The nucleus has them firmly gripped in its gravitational pull and they’re uninterested in going anywhere. This area of grounded electrons is known as the valence band. In order for them to be available for any sort of exchange, they’ll need to get farther away from that nucleus, and out into an outer band of the ion, conveniently known as the conductance band.
How does this all relate to the parking lots I mentioned in the title? I’m glad you asked. The parking lot analogy is a fantastic illustration of the process by which light interacts with matter. Let’s think of it this way: the nucleus of the silver halide ion is your typical Big Box Store. Directly outside of the store is the valence band parking lot, full of electron cars, all off, all waiting in the ground state. Beyond the parking lot is a strip of grass, which we’ll get to shortly, and beyond that is the conductance band (i.e, the road), where the cars are all in motion, on their way to any number of places.
The parking lot analogy, illustrated, from AIC’s Photographic Chemistry for Preservation, unit 2, “The Latent Image.”
In order for the cars to get out of the valence band, they’re going to need some energy. For our electrons, the needed energy is light. Once they get light to get the engines going, they can pull out of the parking lot and onto the road and drive off to chemical reactions.
Now let’s detour briefly to that grassy strip that I mentioned earlier. It’s known as the forbidden gap. Ideally, this area is empty. However, due to defects such as insufficient energy, an electron may not be able to completely cross to the conductance band, and may be temporarily stuck in this gap. Even here they can be useful as stepping stones for other electrons that need to cross over. Stuck electrons will either receive more energy to get them to the outer bands, or they’ll lose energy and be pulled back to the valence band.
I’ll note here that this structure is characteristic of all semiconductors, including digital camera sensors. In silver halide grains, this excitement of electrons will always happen when it comes into contact with light, as silver halide has a light sensitivity of 100%. No matter what, when a grain of silver halide is exposed to light, it will always liberate an electron. You also needn’t think of it as just one electron at a time being excited in this fashion. The grain can have so much energy that its valence band is completely empty, and vice versa.
What happens after this? Well, that’s an exploration for next time.
Hyacinth Tucker (UCL) — Bindery and Conservation Technician
About two years ago, I set upon a mission to gain expertise in the area of identification and treatment of photographic materials. Under the guidance of our conservator, Ashleigh, I developed an education plan that was split between the theory of learning the ins and outs of photograph identification, and the hands-on work of treating pieces that came into the Lab. Of course, these two things go hand in hand. If you can’t identify a piece, you can’t treat it correctly, right?
Fast forward to last year. With the start of the pandemic and the transition to working from home, my education plan changed radically. If I’m not in the Lab, I can’t spend much time on treatment, so I had to get a little creative and work on other ways to learn more.
I am about halfway through the series; a triumph for me, as I have never been one for the study of chemistry. I will say that while it is still very technical, I’ve had a lot of good pegs to hang the information on, owing both to my earlier studies in photograph conservation and my personal history with film photography. It’s been a tremendous thing, viewing things that I learned as a photography student from a different angle. So far, it’s been a great journey.
In this series, I will share with you some of the most fascinating things that I’ve learned so far. My aim will be to keep the technical as simple as possible, for those of you who are like me, still coming to terms with the deeper science. The small bites help it all make sense, I promise. Hopefully, you’ll find it all as interesting as I have.
Before we can understand anything else, we need to talk about halides. What are those and why are they used in photography? Good questions! Halide salts are derived from halogens, which occupy group 7A (column 17) of the Periodic Table of Elements (see below.) Halide salts are used in photographic emulsions that are spread over a substrate (such as paper or film) before the substrate is exposed to light. The silver halides react to the light to form an image when developed.
I should note here that silver gelatin prints, albumen, and collodion photographs all utilize silver halides in their chemical composition. However, silver gelatin is unique among the three in that it is the only one that uses a true emulsion; in albumen and collodion coatings, the halides rest on the surface.
Photograph – silver gelatin process
Photograph – albumin process
Photograph – collodion process
In forming the silver gelatin emulsion, halide salts are combined with silver nitrate and water to form silver halides, the compound at the core of silver gelatin photography. Silver nitrate is pretty much universally used regardless of halide salt, as it is water soluble (it dissolves) but not too much so. The freed silver will look for a bond partner, and the halides in halide salt fits the bill. As a result, silver nitrate, when combined with a halide salt in water, will result in silver halide and a left over salt.
This reaction, which seems like a lot, I know, is referred to for our purposes as “The Emulsification Equation.” To refresh our memories a bit, an emulsification is a liquid (here, gelatin) that contains fine particles of another liquid (the silver halide) without fully combining. Think mayonnaise, or butter. (This isn’t perfectly analogous, as silver halides are crystalline solids and not liquid fats, but the basic idea is the same.)
Chemically speaking, that reaction looks like this:
Equation for emulsification
As a quick reminder, Ag = silver, N = Nitrogen, O = Oxygen, K = Potassium, and Cl = Chlorine.
Now, if you’ll look at the image of the halogen column of the table below, you’ll see a number of options for salts to combine with silver nitrate. Older emulsions involved bromine or iodine; more modern emulsions tend toward chlorine. Crystals formed from silver chloride salts are much more uniform in structure, which makes its use outcomes much more predictable.
Salts that will combine with silver nitrate
I’m sure you’ve noticed that we’ve got a couple of halogens unaccounted for, namely fluorine and astatine. Neither of these are used for this kind of work, and for good reason. Fluorine, for its part, is very water soluble. Very water soluble. To put it in perspective, sodium chloride (regular table salt) is about 35% water soluble. I’m sure that in the course of cooking, we’ve all dissolved salt in water, and you can recall how relatively simple that is to do, though not without some small effort. Well, fluorine salts are about 172% water soluble! You could use it for your emulsion, but moments after developing an image in a water-based solution, you’d see it dissolve before your eyes.
I’ll note here very briefly that chlorine, bromine, and iodine are also more soluble than table salt, but not nearly as much as fluorine, making them perfect partners for our silver ions.
Meanwhile, astatine is…well, it’s radioactive. I think you can see the problem with this one.
And there you have it, a short and hopefully painless explanation of the humble halide in silver-based photography. In the coming months, we’ll be looking at other fascinating aspects of halides and our Emulsification Equation.
Hyacinth Tucker (UCL) —- Bindery and Conservation Technician
At the end of last year the lab purchased a modified UV-Vis-IR Nikon through MaxMax so that we can start to play around with infrared photography. Infrared photography (IR) is commonly used in fine art conservation as an examination tool. Reflected IR can be helpful when trying to identify pigments, inks, coatings, etc. and transmitted IR can helpful for viewing watermarks, underdrawings, and linings. We’ve only just started dabbling with IR photography, but I wanted to share some photos from my most recent session with reflected IR.
This is a full leather photo album from the Public Library of Cincinnati & Hamilton County’s collection. This early 1900s photo album contains hand-colored silver gelatin photographs taken by A. Nielen. The photographs appear to depict his travels through the US and Canada, and various landmarks and neighborhoods of Cincinnati are represented.
Before treatment
After treatment
This seemed like a good object for reflected IR because of the hand-coloring on the photographs and the white ink inscription below each photograph. I began by taking a representative visible light image (first image below) using our modified UV-Vis-IR camera, incandescent lighting, and the X-Nite CC1 filter on our 50mm lens. Then, being careful not to move the position of the camera or the object, I switched to the X-Nite 830 filter (830nm) and converted that image to grayscale in Photoshop (second image below). Then I took my visible light image and my reflected IR image into Photoshop to create the false-color image (third image below). The digital false-color image is a combined representation of the visible and infrared images, and it’s actually quite simple to make. You basically copy and paste the various channels for the VIS and IR image as follows, green to blue, red to green, and IR to red. The false-color image allows you to better differentiate and characterize the various materials (pigments, inks, etc.) and potentially even identify them if you have sufficient known samples to use as references.
Normal illumination
Near infrared with wavelength at roughly 830nm
False color
Like I said, we’ve only just started using IR and we’ve got a long way to go, but I’m looking forward to experimenting and learning more about it as time goes on.