Special Photography for Larger Objects: Photogrammetry

By Christy Ching

Conservation Technician Christy Ching photographing the underside of an Egyptian coffin 2017-20-1.3 for photogrammetry.

One project I have really enjoyed working on as a pre-program conservation technician is documenting larger objects for a process called photogrammetry. Photogrammetry is a technology that gathers spatial and color information of an object from multiple photographs to form a geometrically corrected, highly detailed, stitched image called an orthomosaic. Essentially, photogrammetry creates a distortion-free, three-dimensional model of an object based on two-dimensional photos of every surface photographed in sections. 

Left: Four photographs of an ancient Egyptian coffin lid L-55-16B at various angles, which were used to create a 3-D model. Right: 3-D model draft of L-55-16B.

*L-55-16B (21-46-9) is a loan object from the Philadelphia Museum of Art (PMA)

This can be done for objects of any size. However, we are mostly reserving this technique for larger objects, specifically larger textiles and Egyptian coffins. This is because photographing the coffins and textiles normally with a single shot requires a greater distance between the object and the camera in order to fit the entirety of the object into the frame, and doing so reduces the image quality. Not only that, but the camera distortion that is inherent in all photographs will become more obvious. The resulting image will not be an accurate representation of the coffin or textile, which is not ideal for documentation purposes. 

The image on the left is a single-shot photograph of L-55-16B while the image on the right depicts the same coffin lid created by photogrammetry. When comparing the two images, the camera distortion in the single-shot photograph can be seen especially in the feet and head of the coffin lid.

With photogrammetry, we can take parts of the 3-D model and use them as high resolution, distortion-free, 2-D images of the object instead.

Six views of L-55-16B depicting the top, interior, and the four sides of the coffin lid generated using photogrammetry.

So far, a little less than ten coffins, a few textiles, a pithos fragment, and a giant granite relief have been documented using photogrammetry. The models and orthomosaic images are all generated by Jason Herrmann from CAAM, and we are very grateful that he is doing this for us! To learn a little bit more about the photogrammetry process, view this Digital Daily Dig here.

This project was made possible in part by the Institute of Museum and Library Services.

An Ivory Figure from Hierakonpolis: Part II

By Tessa de Alarcon

E4893 before treatment

The figure you see here E4893 is an ivory statuette from the site of Hierakonpolis. In a previous blog post I discussed the X-radiography that helped me determine that the large fill around the waist of the object could be safely removed. Based on that X-ray, I was able to mechanically remove the soft fill material and separate it from the object.

E4893 during treatment: both images show the object during fill removal.

Sometimes the full picture is not always clear from an X-ray. While I was able to remove the fill material and the nails, one thing that was not apparent on the X-ray and only became clear during treatment, is that part of the lower half of the object was embedded in the fill. This section also keys into the upper fragment. This may seem like a minor detail, but it is very important for knowing how the pieces should go back together. The loss in the waist is large and a fill is needed to stabilize the object structurally. One worry I had as I approached this treatment, was figuring out what the fill should look like and how elongated should the body be. However, once I found that in the fill there was a section of the object that keyed the bottom and the top pieces together, I knew that the placement of the two fragments could be conclusively determined.

E4893 During treatment: after the break edges were cleaned. The red arrows point to the part of the object which determines the size of the fill as it fits into the break edge of the top half of the object.

Even knowing how the pieces should go together joining the pieces was far from straight forward. The point of contact is too small for an adhesive join without fill material taking the weight of the fragments or to relay on the connection to hold the pieces in alignment during loss compensation. I had to instead figuring out how to support the fragments in the correct alignment while I created the fill. I decided that the best way forward was to create a removable fill using an epoxy putty. This is a fill that has to be adhered in place, as if it were another fragment, rather than relaying on the fill material to adhere or lock the fragments together. This means that I needed a barrier layer between the fill material and the object, and a system to hold the pieces together. The barrier layer is meant to prevent the fill material from sticking or adhering to the object and you will see in the images below that there is cling film between the epoxy and the object that I used as a barrier layer. The support system, however, took some trail and error before I found a method that worked.

E4893 during treatment on the left is the first attempt at filling the loss with the object resting flat. The image on the right shows the object during the second attempt using a foam support system inspired by the rigging at CLA.

First I tried laying it flat in a bed of glass beads to support the object, but this did not work, it was too hard to see if I had everything lined up correctly and the fragments kept shifting as I put the epoxy in place. Taking inspiration from my colleagues working on Egyptian monumental architecture at the conservation lab annex (CLA). I decided to try making a rigging system in miniature to hold the fragments in place vertically. This allowed me to see the object all the way around and check the alignment more reliably. However, my second attempt using a vertical support system with the object upside down, still led to too much shifting when I tried to put in the fill material.

E4893 during treatment images showing the final system used to support the fragments during placement of the fill material. The image on the left shows the back during fitting and on the right is a view of the front after placement of the fill material.

As a result, I adjusted the system from the second attempt and put the object right side up, carved a chin rest for the figure into the foam support and added a piece of foam to the back to hold the upper fragment more securely in place. The wooden skewers you can see in the images are used to hold the foam pieces together. My third attempt was very effective at holding the object in place in a rigid way with no shifting and gave me plenty of visibility to check the alignment.

E4893 during treatment. The image on the left shows the object with the fill dry fit into place (no adhesive had been applied yet). The middle and left images show the object after the fill was adhered in place and the gaps filled.

After I made the fill, I sanded it smooth and checked to make sure it fit right. Here you can see if dry fit in place and after everything was joined together. This should be a much more reversible treatment than what was done before should this treatment need to be redone again at some point in the future. While the object does not look all that different from the way it did before treatment, it is much more stable now with materials have better aging properties and allow for easier retreatment should that be needed.

E4893 After treatment

This project was made possible in part by the Institute of Museum and Library Services

An update on Kaipure’s funerary chapel

By Jessica Betz Abel and Julia Commander

Greeting everyone – there’s a lot to update on from our Conservation Lab Annex (CLA) but for this post, we’re going to focus on the recent progress of Kaipure’s Funerary Chapel. It has been a while since we posted about Kaipure, in fact the last time we posted was almost exactly three years ago. As a quick reminder, two of the walls (the south and east) from the chapel were most recently on display in the Lower Egyptian Galleries, but they were disassembled and deinstalled in 2015 as a precautionary measure due to nearby construction. This also allowed us to proceed with much needed treatment of the flaking limestone and paint as well as designing a new support system in anticipation the entire chapel being reassembled in the new Ancient Egypt and Nubia Galleries. The complete chapel has not been on display in over 25 years!

Here at CLA we are working on building one of the smaller walls as a proof of concept for our engineering team. The south wall is the smallest section and so that is where we decided to start. But before we could begin, we had to locate all the blocks and bring them down from the rafters. 

Julia Commander using the forklift to retrieve blocks from the south wall of Kaipure.

With all the blocks needed for the south wall, we started by erecting the bottom course of stones. Once those were in place and shored up with temporary wood and foam pegs, we laid the first stretcher course on top.

The first two courses of the Kaipure chapel south wall.

In antiquity stones would have been assembled using a mortar, however, using a mortar in an indoor gallery setting is not necessary or practical. Mortars require quite a bit of water for application and that could potentially mobilize any lingering salts in the limestone which could compromise the structural integrity of the stone. Mortar is also much less reversible than many of our other options, not to mention the mess it would create during installation. Instead, we have been investigating interfaces of various materials that would replace the need for mortar or adhesive at all. For Kaipure, we have narrowed down our options to Silicone Rubber and Sorbothane. Both materials have good viscoelastic properties, reduce point loading, distributing the weight of the stones, and providing a grippy material between each course to lock the stones together.

Comparing the working properties of Sorbothane vs. Silicone Rubber.

In addition to the interfaces, we are currently working with our project engineers to design an armature on which each wall can be assembled. The armature will provide the stability and support that many of the individual stones need. In order to not cause any further damage to the stone, we are opting to use the existing holes which were drilled into the backs and sides of the stones during a previous installation. Though we are still very much in the early stages of design we are excited by the prospect of seeing the entire chapel reunited in a few short years!

IMLS? What’s that?

by Lynn Grant, Head Conservator

If you don’t work in the Museum or Library field, you may never heard the initials, ‘IMLS’. But to many in those fields, it’s a lifeline and important source of support and information. In 2019, the latest year with information, the Institute of Museum and Library Services (IMLS) awarded $223.5 million through grantmaking, research and policy development, to advance, support, and empower America’s museums, libraries, and related organizations. The Penn Museum has received support from the IMLS on many occasions.

Coffin lid of Djed-Hapi (E3413A)

In 2015/16, the Museum moved its Egyptian Collections off-site in order to protect it from vibrations associated with the construction of a large building right beside us. This gave us the opportunity to carry out an inventory and examine the objects in storage to determine which needed conservation. But it’s a huge project; we had originally believed the collection was 42,000 artifacts; it turned out to be more like 50,000. In order to fund such a massive undertaking, we break it down into manageable chunks. In 2019, the IMLS awarded the Museum $250,000 to fund the conservation of a group of Egyptian and Nubian coffins and related funerary goods. This enabled us to have two project conservators dedicated to this group of artifacts, as well hiring two conservation technicians to photograph items for the public database. Despite the pandemic, we’ve been working away at this since October 2019 and will complete the work by the end of September. Over the next few months, the project conservators will be sharing some of their work with you. Enjoy!

A Puzzle without all the Pieces: Treating Papyri

By Jessica Byler

The condition survey of our papyri collection is complete – I counted almost 4,300 fragments of papyrus and vellum, more than we realized were there! The papyrus ranged in size from a few millimeters to 9 feet long. Now, I have moved on to treating a few of the papyri that will be on display in the new Egyptian galleries.

Many of the papyri are sandwiched between pieces of Mylar. Static from Mylar can lift off friable ink or even split the two layers of the papyrus fibers and damage the papyrus. In order to safely remove the papyrus, I use a MinION 2 Ionizing Blower to eliminate the static charge. After removing the papyrus from the Mylar, I can then remove old repairs, realign fragments and fibers that are out of place, and apply new tissue paper bridges. Using a light box can help me identify joins and keep fragments in alignment. Papyrus fibers have different thicknesses, widths, and orientations, so transmitted light from a light box reveals the unique fiber pattern.

Left: Removing papyrus (49-11-1) from a Mylar enclosure using an ionizing blower
Right: Using a light box to realign fragments

Let’s look at one papyrus I am currently treating: a Temple robbery papyrus (49-11-1), dated to the 20th Dynasty or 11th century BCE. Along with removing old materials that might harm or obscure the papyrus, a key reason I am treating this particular document is to make sure the joins are right. It is fragmentary and there have been several treatment campaigns to repair it using a variety of materials, including Scotch tape, Japanese tissue, and Document Repair Tape.

Temple robbery papyrus (49-11-1), before treatment

I removed the old repairs where possible and reassessed the location of the fragments. At some point, several of the fragments have become misaligned or detached. In several instances, the fragments were just slightly out of line and could easily be nudged back into place. However, I quickly noticed some issues with a long fragment on the far left (on the right in the photo of the back below), and a small rectangular fragment at the bottom.

Left: detail of the back of the right section before treatment
Right: Section under transmitted light from a light box, with red arrows pointing to the two fragments in the wrong spot

On the long fragment, there are ink marks either side of the join which do not meet up. If the fragment was in the correct location, you would expect the writing to extend over the break. On the smaller fragment, the color, curvature, and thickness were different than the surrounding fragments. Using transmitted light, it is clear the fibers of these fragments do not actually line up correctly. Although at first glance they might not look out of place, they clearly do not belong there.

Left: Detail of front, with red arrows pointing to ink which does not meet up
Right: Detail under transmitted light, with red arrows showing that the fibers do not line up

The long fragment has two lines of writing at the top, so the number of locations it could join was limited. The small fragment at the bottom did not have any writing on it, so it was harder to determine its orientation and position. To add to this complicated puzzle, these pieces also might not join to any of the extant fragments.

Left: Detail of back during treatment, with the two fragments, indicated with red arrows, properly aligned
Right: Detail of back during treatment, with red arrows pointing the two fragments, and blue arrows pointing to some of the new bridges; areas of white residue from the old materials is also visible

Thankfully, their proper locations were easy to find using a light box. As you can see in the detail photos above, the fibers of the papyrus were a perfect match. The tissue paper bridges I used were around the size of a grain of rice and are clearly visible but blend in nicely with the papyrus. The Temple robbery papyrus is now ready for display!

Temple robbery papyrus (49-11-1), after treatment

This project is funded by the Antiquities Endowment Fund (AEF).  The AEF is supported by an endowment established with funds from the United Stated Agency for International Development (USAID).

Conservation Confidential: Sphinx Gallery tales

Join Schwartz Project Conservator, Molly Gleeson, as she brings you up to date on what’s been happening in our Lower Egyptian Gallery for the last two years. Lots! Almost all of it pretty monumental. Molly will be available to answer questions via the Penn Museum Facebook page between 1 and 2 pm EDT on Friday, November 6.

Picture (im)perfect

Hello again from CLA (or at least from our home offices)! As we’ve mentioned before, conservators love to look at records relating to the objects we’re treating. It helps us to gain insights into the artifact’s history and gives us context for what we see on the bench in front of us. While we don’t always have exhaustive information about every single piece, it’s always interesting to do a little research when we can. One of our recent blog posts discussed how we’ve used archaeological renderings to understand traces of colors on our objects; this post will take a look at how photographic records can inform us about the current condition of the pieces.

Photograph of the Penn Museum Archives
A view of the Penn Museum Archives.
Each of these boxes is filled with a treasure trove of information.

Before the CLA team dove into the hands-on work last fall, we took a trip to the museum’s extensive archive collection to do some digging into the history of Merenptah’s palace. With the help of Alex Pezzati, Senior Archivist, we were able to read through the records of the excavation, led by Clarence Fisher from 1915-1920. Our research was also guided by the work of Dr. Kevin Cahail, whose own forays into the archives have revealed a lot of missing details about the site. He was able to provide a lot of insights into what we were seeing in the photographs.

One of the things that impressed us most about the excavation images is the sheer scale of the architecture. While we’re very familiar with our columns and doorways by now, it’s quite another thing to see them in situ. The picture below shows columns and pylons (trapezoidal gateways) from Merenptah’s Coronation Chapel. These objects were previously exhibited at half height because the ceilings in the downstairs gallery were too low, but they’re about 25 feet tall. Part of our project for the new galleries is to figure out how to display these columns at their full height so museum visitors can experience them the way the Egyptians would have. In the meantime, it’s a useful reminder to look at images like this to remind ourselves that they stood for several thousand years!

Site image of the Coronation Chapel during excavation
The Coronation Chapel mostly excavated. The columns would have had capitals, but otherwise are at their full height.

Another thing you might notice in that image is all the water on the ground. The site is in the Nile flood plain and experienced several very wet seasons. We could tell from the current condition of the stone that it had been waterlogged. Stone is often thought of as being hard and unchangeable, but this particular Egyptian limestone contains a lot of clay, so it becomes very soft when wet. Fisher’s notes talk about how fragile the stone was, and ultimately how they made the decision to bring the pieces back to Penn before they deteriorated even more. The stone was still damp when it was wrapped in linen and packed into wooden crates – which explains the fabric impressions we see in the surface of some of the pieces.

Workers preparing columns for shipping and stone with textile impressions
(Left) Workers preparing the column pieces for shipping. (Right) An example of the stone surface with impressions of the textile weave.

Images from the site are incredibly useful tools when we’re looking at damage to an object and trying to determine the cause – whether the damage occurred before excavation or due to more recent changes. They’re also helpful when we’re trying to figure out the extent of old repairs. When the pylon pieces were installed in the gallery in the 1920s, they were extensively restored with plaster and paint. We could also tell that some lost stone had been replaced with bricks and cement, but it was difficult to tell where the restoration ended and the stone began. Fortunately, there were a lot of pictures taken of the coronation chapel while it was being excavated.

Coronation Chapel pylon
(Left) The left pylon during excavation. Notice that the row of figures second from bottom is almost completely lost. (Right) The same object with plaster reconstruction. The detail was based on the other pylon, which is much more intact.

Looking at the original photographs of the left pylon, we could tell that it had already suffered significant surface loss to the bottom and middle sections. We could also see that even though it was still standing, the middle part had broken into several pieces. Using that knowledge during the deinstallation process, we were able to rig around the damaged areas and to remove the old restoration material so the pieces could be separated. When the pylons are reinstalled in the renovated galleries, they will be safely displayed on custom steel support structures. We’re working on how to replicate the decoration, but we’ll make it clear what is original and what is new.

During our time in the archives, we discovered one thing that hasn’t changed much – archaeologists love site dogs.

Site animals
Some pictures of very good dig dogs over the years… and one very cute baby fox (bottom left)!

The right tools for the (monumental) job

Greetings from the Penn Museum’s Conservation Lab Annex (CLA)! You may remember from our first post the scale (large!) and types of objects we are going to be working on over the next few years. We are mostly working on architectural elements like doorways, windows, and columns that were part of the palace complex of the Pharaoh Merenptah, who ruled Egypt from Memphis from 1213–1203 BC. To put things in perspective, the doorway we are currently working on is over 12 ft tall and many of its fragments weigh hundreds of pounds. That means we have had to add a few new tools that are not typically found in a museum’s conservation lab. Most recently we’ve started utilizing a lot of new tools including a forklift, a gantry, and large-scale sandboxes.  

  • Forklift – A few weeks ago, the whole Ancient Egypt and Nubia Galleries Team attended a certification workshop in forklift operation. The certification course taught us the basics in how to safely operate our electric forklift. Having our own forklift onsite allows us to easily move some of the large stone fragments in and out of the lab, reorganize the layout of the warehouse to create space for rigging and lifting, and organize all of the Merenptah Palace pieces into one area.   
Egyptian Section Curator Dr. Jennifer Wegner smoothly maneuvering the forklift during our training session.
  • Gantry – At CLA we have a gantry crane in the warehouse which allows us to rig and lift some of the heaviest objects and fragments. This is especially important when we are trying to dry-fit pieces together before making more permanent joins. There are lots of different ways to rig or strap a fragment for lifting, but we’ve found that using shorter straps with a choke hitch is the safest way to lift our artifacts. In the photo below you can see that’s exactly what we’ve done. Once we have the straps secured and fully supporting the object, we begin to slowly lift, making sure the straps settle and don’t slip or re-adjust, dropping the object.  
CLA team using the gantry to lift part of the lintel from Doorway 1.
  • Sandbox – Sandboxes are often used in conservation to support objects during joining. Using a sandbox, we can place an object inside at whatever angle we need to in order to support the object on top with nothing but the weight of gravity. At CLA, our objects are quite large, so we are using old shipping crates and converting them into large sandboxes to accommodate our needs. In the photos below you can see the process of moving a fragment into the sandbox and then in the second photo you can see that fragment has been placed in such a way that it can now support the weight of the second, joining fragment on top of it. The blue tape serves as a guide to help us know exactly how the two pieces fit together once we have applied the adhesive and are ready to do the final joining. 
CLA team moving part of the lintel from Doorway 1 into a sandbox.
Fragments of Doorway 1 lintel being dry-fit together in the sandbox prior to joining.
  • Dremel – Lastly, and on a much smaller scale, we’ve been using a few different power tools. The most helpful so far has been the Dremel. While the Dremel is not a completely foreign tool to many conservators, it is most often used for making mounts or sanding fills and/or cross-sections. In this case we are using the Dremel to cut and remove all restoration pins that have become heavily corroded over the years, expanded, and are causing damage to the stone.   
Corroded ferrous pins from a previous restoration being cut and removed from Doorway 1 fragments.

As with any job, having the right tools is really important, for success and safety! We look forward to continuing to share the progress we’ve made on this project from our home offices, as we continue to work from home.

Papyri Project

By Jessica Byler

This fall, I started a survey of our Egyptian papyrus collection thanks to an ARCE (American Research Center in Egypt) grant. The goals of the survey include preparing and rehousing the collection to be moved to a new storeroom, identifying unstable papyri that need to be treated, and getting some of the papyri ready for exhibit. The Penn Museum is in the process of redesigning the Ancient Egyptian and Nubian Galleries, and the curators have identified around 70 papyri they would like to include. Part of my job is treating and rehousing these papyri and making recommendations on their display.

E16423, a private letter in Arabic

What is Papyrus?

The papyri in our collection are mostly manuscripts. A sheet of papyrus is made of two cross-laminated layers of thin fiber strips made from the stems of the papyrus plant (cyperus papyrus). One layer of fibers is laid vertically, and the other is laid on top horizontally, creating a sheet with a grid pattern. Individual sheets were then overlapped and joined to create rolls. These rolls could be used as a single, long sheet or could be cut down as needed. The side with the horizontal fibers is called the recto (think “right side”), and the side with the vertical fibers is called the verso (think “reverse”). Scribes often wrote on the recto along the horizontal fibers, though some scribes wrote against the fibers or on both sides of the sheet.

A piece of modern papyrus through transmitted light
E2751, some vertical fibers are missing, revealing the horizontal fibers from the other side

Looking for a join helps identify the recto. Most joins are horizontal fibers to horizontal fibers, though some are horizontal to vertical. Look along the horizontal fibers and see if they continue across the sheet. If they do not line up or if there is a clear overlap, that’s likely a join.

E16323, horizontal to horizontal join. The red lines indicate the direction of the fibers and join.
E16411B, vertical to horizontal join. The red lines indicate the direction of the fibers and join.

Scribes used brushes or reed pens to write on the papyrus sheets. Inks were made from mixing ground up pigments into a binder. The most common ink was carbon black or soot bound with gum to make black ink. Scribes also sometimes used red ink made from red ochre, iron gall, and sepia, among other pigments. Some papyri are thickly painted with gypsum, metal oxides, and earth pigments.

E3068, a painted papyrus manuscript
83-1-1I, a manuscript with both carbon black and red ink

Penn Papyrus Survey

The Penn Museum has around 1200-1800 papyri featuring a wide range of personal, legal, administrative, literary, and religious texts in six languages: Arabic, Greek, Coptic, Hebrew, Demotic, and Hieratic. The collection spans around 4000 years, from the Old Kingdom to Islamic Egypt. These include Books of the Dead, Homer’s Iliad, and the Gospel of St. Matthew. There are also groups of small fragments which have not been reconstructed or studied. The Penn Museum’s collection of papyri has never been the subject of a concerted conservation campaign – until now.

Most of the collection is currently encapsulated in Mylar and stored flat in manila folders or sandwiched between two glass plates. I am surveying the collection at the object-level, one by one. I examine, measure, and record each piece, noting the structure of the papyrus, how it is housed, old mends or treatments, condition issues, and if it needs to be rehoused or conserved. I follow the examination and documentation with photography. Images are available on our Digital Collections webpage.  Hopefully with the new photos and documentation, this collection will be more accessible to papyrologists and scholars around the world.

Photographing papyrus using a copy stand

More Information

Eventually, the information on the Penn Museum papyri collection documented in this survey will be included in the Advanced Papyrological Information System (APIS) database, where only a small fraction of our collection is represented today. There are a number of great resources if you would like to know more about the structure and conservation of papyrus. The University of Michigan, which holds the largest collection of papyri in North America, is active in papyrological research and education. The Brooklyn Museum and NYU have both recently done similar projects and have great blogs about their collections as well.

This project is funded by the  Antiquities Endowment Fund (AEF).  The AEF is supported by an  endowment  established  with  funds  from  the  United  Stated  Agency  for  International Development (USAID).

Shades of the Past

By Julia Commander, Jessica Betz Abel, and Anna O’Neill

We’ve shared a few insights into the monumental limestone we’ve been treating at our Conservation Lab Annex (CLA). You may have noticed a consistent color scheme: tan. The surfaces of the doorways are intricately carved and decorated with faience inlay, although we mainly see a variety of neutral tones.

Doorway 1 in the lab

To get a sense of how these architectural elements would have looked when they were made in Memphis, Egypt around 1213–1203 BCE, it helps to understand the materials and their state of deterioration. Luckily, the Penn Museum Archives has extensive records from the 1920’s Memphis excavations, which provides some further clues about these objects.

Searching through archival materials, we found detailed notes about each object as it was excavated, as well as extensive watercolor illustrations. We can see brilliant colors in the drawings and notes referencing traces of paint and inlay material.

Archival illustrations of Merenptah columns
Archival illustrations of Merenptah columns

We even see that the doorways are illustrated with brilliant blue and teal colors.

Archival illustrations of Merenptah palace doorways
Archival illustrations of Merenptah palace doorways

Some of the illustrations appear to extrapolate data from small traces of material. Do these colorful illustrations line up with what we’re seeing now in the material itself?

To explore a little further, we brought the Crimescope out to CLA to investigate using multispectral imaging. This technique has been discussed on the blog before, and we were particularly interested in infrared (IR) imaging of the faience inlay. While there are different types of faience material, some types related to Egyptian blue pigment produce the same luminescent response induced by visible light.

Searching for IR luminescence pointed us to a tiny area of inlay in the upper corner lintel fragment. The tip of one stripe glowed brightly, which corresponds to a pale green color that’s visible in normal lighting.

Visible light (VIS)
Visible-induced infrared luminescence (VIL)
Detail with VIS/VIL overlay

This result suggests that we’re seeing a deteriorated state of formerly bright blue/green/teal faience. While we did not see every trace of the degraded inlay light up in infrared imaging, this small hint corroborates what we’re seeing in the archival illustrations.

We plan to continue using multispectral imaging to explore decorated surfaces when we’re back at CLA. Stay tuned!