Equipment choices for Visible Induced Infrared Luminescence

by Tessa de Alarcon

Since we have posted often about visible induced infrared luminescence (VIL) and the equipment we use at the Penn Museum, we on occasion get emails from other conservators and museum professionals asking about what equipment to buy and the costs associated with this photographic technique. This technique is often used for imaging Egyptian blue, but it can also be used for Han blue and Han purple. Much of the same equipment is also used for infrared reflectance.

E1827A-E multimodal data set including a visible image (left) and infrared reflectance image (center) and a visible induced infrared luminescence image (right).

Making specific equipment recommendations though are tough because there are a lot of options and a lot depends on your budget. Basically though, what you need are the right lights, a camera (and lens), and a long pass filter for the camera to capture in the infrared. I thought I’d do some testing to show how some these different elements impact the results in the hopes that it might help others figure out budgets, and to show that it’s also possible to build this equipment up piece meal, starting with equipment you might already have or is very low cost. Some elements though are pricey and things can add up.

All of the VIL images in this blog post also have a Spectralon standard in them (99% infrared reflectance standard). This is not low cost, and not required for the technique. It is often required for publication, and is useful for trouble shooting or developing new techniques. I’m mentioning this because it is useful to evaluate the data presented here, but it isn’t something that is strictly required. We did not have one for a long time, but were able to do this type of imaging. We waited as it was a big investment for us (approx. $500). These standards also range in price depending on the size and calibration.

An infrared (IR) filter is a requirement for this technique. I only tested one IR filter (though we have two). They range in cost depending on where you get it and the quality of the filer and the size of the filter. Ours is a B+W and is an 830nm IR long pass filter and is 62mm ($130). There are cheaper ones available as well as more expensive ones too. We got ours to fit our macro lens, and have adaptor rings (all our rings are generic brand low cost ones that were each under $10) to fit it onto other lenses that we have.

The right lights are a critical factor for this technique, but not necessarily one that has be high cost. You need a bright light with no infrared radiation, red lights are commonly used and LED bulbs are preferred as they produce no infrared radiation. I tested out three different lights for visible induced infrared luminesce. These include at the high end of the budget a Mega 64 Profile Plus RGB + UV Par light at maximum intensity with the red LEDs on only. This is a roughly $200 light. The other lights I tested are both low cost options. I tested one FEIT electric one red LED light bulb I put in one of our extra reflectors and photo light stands. I bought this bulb for $6 from my local hardware store, and a two daylight LED bulbs (UL certified) that I got from our facilities department to replace burnt out bulbs on our copy stand. I used both bulbs in the regular copy stand set up for imaging. I don’t know what the bulbs I got from facilities cost, but there are no brand name stamps on them so I’m guessing they weren’t expensive, that UL logo on it just means that it is a UL certified bulb.

The Mega 64 profile plus (left), a daylight LED bulb (center), and a red LED bulb (right)

I tried both our full spectrum modified camera, and our regular digital SLR (unmodified). Neither of these is an inexpensive camera, but should show generally the difference between using what ever digital camera you already have, and getting a similar cost one as a modified camera. Neither is new, we use our cameras until they can’t be repaired. The unmodified camera is a Nikon DSLR D5100 and the modified camera is a Nikon DSLR D5200. We bought our modified camera new, and sent it to Life Pixel to remove the internal filter, but they now sell used cameras that they will modify for you (there are options). Ours was modified to be a full spectrum camera. At the time of writing this post, the most economical option I saw on life pixel for a used camera with this modification package cost a total of $449. So even used not cheap. But lets get to the testing and start looking at results.

Lets get to the results from the modified camera. I have a visible reference image in the set, and the VIL images using each of the different lights. All the lights worked, but the brighter MEGA par 64 gave the best results, especially at exciting traces of Egyptian blue. Though the daylight no-name brand LED bulbs were not bad. These have a range of camera settings, and the benefit of the modified camera is that I could see the results in live view, focus the image and adjust the settings with minimal bracketing. The spectralon should not be visible, and if it is usually means that the image capture settings are not quiet right.

Modified Camera results: visible reference image (top left), VIL image with the MEGA 64 LED lights (top right), VIL image with the no-name daylight LED bulbs (bottom left), and VIL image with the RED LED bulb (bottom right).

Next up, the unmodified camera. The images are arranged in order of the lights used the same way as for the modified camera for easy comparison. So I did get results with all of the lights. The down side is that the live view shows nothing so the focus can’t be corrected. These images are all slightly out of focus because the focus in IR is different from the focus when capturing in the visible range and I focused the image before putting on the IR filter. All of them had to be taken at the longest possible exposure of 30 seconds. This made data collection easy since I had no choice in settings. And for the low costs bulbs it looked like they were just black with no data until I got them in adobe camera raw and converted them to grey scale by adjusting the saturation to -100. Then I could see something, but I did also adjust the exposure for the images you see here. You can see the spectralon and the background in all of the images and interpretation might be harder with these than the images taken with the modified camera. I will say I think this could be used for detecting Egyptian blue, but it’s important to note that the unmodified camera only got the thick areas of Egyptian blue, and didn’t have the sensitivity to pick up the traces visible in the images taken by the modified camera.

Unmodified Camera results: visible reference image (top left), VIL image with the MEGA 64 LED lights (top right), VIL image with the no-name daylight LED bulbs (bottom left), and VIL image with the RED LED bulb (bottom right).

For fun, I also tried putting the IR filter over my cell phone and using the MEGA par lights took a photo. This is just to show that even a small sensor like what is in a cell phone camera can work. It is out of focus though and like with the unmodified Nikon DSLR you aren’t getting traces of Egyptian blue. But it did show something, and I could see the results in the live view. This is also an avenue that I know others are working on: producing low cost modified cell phone cameras with built in filter wheels. Sean Billups has presented at AIC on this topic.

Cellphone VIL image: unprocessed and shown as shot with an 830nm IR long pass filter over a an unmodified cellphone camera

To wrap things up, I think it is possible to build this equipment up overtime. You can start with the camera you already have for documentation, and then get better lights and a camera as you can afford them. The IR filter can also be used for IR reflectance, this is also possible with any digital camera with a long exposure and using any light that produces infrared radiation. There is much less difference in data quality between a modified full spectrum camera and an unmodified camera for this method, though again there is no live view and sharp focus is hard to do with an unmodified camera. We use incandescent photo floods (real bright and toasty) but any light that gets warm probably produces infrared radiation and could be used. Daylight for example works real well too (and is free).

Infrared reflectance images (left) and infrared reflectance false color images (right). The modified full spectrum camera was used for the images on the top and the unmodified camera was used for the images on the bottom.

Party Time or New Photo Light?

By Tessa de Alarcon

The conservation department recently acquired a new light for multi-modal imaging – an ADJ MEGA PAR Profile Plus (one for use at the conservation lab annex and one for the museum main lab). The MEGA PAR is a tunable LED light source, with 64 different color channels. While not designed for analytical imaging, it provides a bright and large spot size that we can use for visible induced infrared luminescence (VIL) imaging of Egyptian blue. It will also be something we can use to test out other imaging methods in the future. Taking VIL images is not new to the lab, but the light source we had been using stopped working and we needed to replace it. We are grateful to Bryan Harris for making the purchase of the new equipment possible.

The spectralon and the new MEGA PAR Profile Plus light (right) and the new equipment in use (left)

Along with the new light, we also acquired a new reference standard, a 99% reflectance spectralon. This standard is critical for developing methods and standard procedures for imaging in the lab. In this post I am going to show an example of how this standard can be used and how I developed a protocol for VIL imaging with the MEGA PAR light.

Set up for round one testing: Egyptian green (left pigment sample) Egyptian blue (right pigment sample) and a V4 QP grey scale card.

Since the MEGA PAR light is new, one of the first things I did when it arrived (after unpacking it and reading the instructions of course) was run a variety of tests on known reference materials to see what settings might work for creating visible induced infrared luminescence images of Egyptian blue. As part of that process, I set up a grey scale card (QP card V4) and two reference pigment samples, Egyptian blue and Egyptian green (both from Kremer pigments). I chose these so I would have a known pigment that should luminesce, the Egyptian blue, and one that should not, the Egyptian green. Using the department modified full spectrum camera, I took a visible reference image of the known pigments and the QP card using our regular fluorescent photo lights and a visible bandpass filter over the camera lens so that I could have a normal color image.

Screen shot of thumbnail images of the round 1 testing

Then I captured a series of images using the same set up but replacing the visible band pass filter with an 830nm long pass infrared filter so that I could capture images in the infra-red, with the fluorescent light turned off and the MEG PAR turned on. Each of the images I captured were with the same settings on the camera and with the MEGA PAR light in the same position, just going through each of the 64 color channel options.

Screen shot of Adobe Camera RAW showing the process for evaluating the response of Egyptian blue to each setting

I converted the images to grey scale adobe camera RAW by sliding the saturation level from 0 to -100, so that the red, green, and blue values (RGB) would each be the same. I then used the dropper tool to take a reading over where the Egyptian blue standard is in each image and recorded the number. The higher the number, the brighter the luminescence.

Set up for round 2 testing with the Egyptian blue pigment sample (top left), the Egyptian green pigment sample (below the Egyptian blue), the 99% reflectance spectralon standard (right), and a V4 QP grey scale card (bottom).

After doing that I had a reduced set of options that produced good luminescence in the Egyptian blue for a second round of testing. For round two I did the same thing with the more promising group, but also included in my images the 99% reflectance spectralon standard so that I could check and verify that the light is not producing infra-red radiation. If there is any infra-red, than the 99% reflectance standard should be visible. None of the second round of options showed any infra-red. While any of them can be used for VIL, CL08 gave the strongest response.

Screen shot of round 2 testing evaluation

After developing a working set-up, I did a test in the photo studio using an object that I knew had Egyptian blue, and the standards. I captured a visible image with the modified camera with the visible band pass filter and the fluorescent photo lights, and a VIL image with the 830nm long pass filter and the CL08 setting on the MEGA PAR. The false color image was created by splitting the color channels on the visible image in photoshop, discarding the blue data, and putting the VIL data in the red channel, the red visible data in the green channel, and the green visible data in the blue channel. As you can see the spectralon is not visible in the VIL image meaning there is no IR radiation being produced by the MEGA PAR light.

Images of E12974 with a visible image (left), a visible induced infrared luminescence image in the center showing Egyptian blue in white (center), and a false color image showing Egyptian blue in red (right).

After all this work, I had an opportunity to see how the new light would perform in less than ideal settings. I have been working on a study of one of the coffins in the collection, 2017-20-1.3, to examine the coatings and pigments. VIL is the perfect method of identifying blue areas on the coffin but the coffin is too big to fit in the department photo studio. The set of images below were taken in the Artifact Lab (our public lab in a gallery space) where there is IR from the windows (daylight) as well as from the gallery lights. I hoped that a short exposure with the new very bright MEGA PAR would reduce the effects of IR in the image. As you can see in these photos below, the 99% reflectance spectralon is slightly visible but not as clearly as the Egyptian blue on the coffin. These results are much better than what we used to get in the Artifact Lab using our old light, so I am very happy with these results.

Detail from the coffin 2017-20-1.3 with a visible reference image (left) a VIL image with Egyptian blue in bright white (center) and a false color image created by combining channels from the visible reference image with data from the VIL image resulting in the Egyptian blue showing up as red (right).

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!

Considering Cleaning

Julia Commander is a third-year graduate student in the Winterthur/University of Delaware Program in Art Conservation. She is currently completing a curriculum internship at the Penn Museum.

It’s time to check back in with the Ptah-Sokar-Osiris figure. In my last post, I mentioned a few of the condition concerns including a significant darkening over the front surface. The uneven surface poses interesting challenges for cleaning, and there are multiple approaches and methods to consider.

Before cleaning proceeds, it is important to understand both the nature of the surface discoloration and the properties of the paint layers. Egyptian objects are not always straightforward, and Ptah-Sokar-Osiris figures have a broad range of condition issues and treatment histories. Check out the British Museum’s online collection for a fascinating look at comparable figures. Discolored or yellowed varnishes have been observed on Egyptian painted surfaces, such as the shabti box described in a previous post. One way to assess surface discolorations is ultraviolet (UV) light illumination, a non-destructive lighting technique. In the UV portion of the energy spectrum, aged coating materials including varnishes and adhesives often fluoresce brightly. Areas that absorb more UV light appear darker in comparison. For this figure, areas of fluorescence do not appear to correspond to the pattern of discoloration, which is most noticeable on the platform under the feet.

L-55-29. In normal light (left), you can see the darkened surface of the front of the figure. In ultraviolet (UV) illumination (right), specific areas fluoresce. The pattern of UV fluorescence does not correspond to the discolored areas or suggest an overall coating.

Additionally, the surface darkening extends over large areas of damage and paint loss, suggesting that it occurred later in the object’s history. In an attempt to understand the darkened surfaces, I will take cross-section samples, which involve tiny (less than 1 mm) flakes of the paint layers. By looking at the edge of a paint flake under magnification, I can observe the stratigraphy from surface down to ground level. One way to visualize this technique is to think about slicing a cake to see the layers inside. To make handling tiny paint flakes easier, they can be mounted in resin for observation under magnification. Through normal light and UV light microscopy, the presence of discrete coating or soiling layers may be observed.

To characterize the behavior of the paint layers, solubility tests were conducted under magnification with small amounts of solvent on cotton swabs. For this painted figure, surfaces appeared to be water sensitive but relatively stable in other solvents. This finding is consistent with typical Egyptian paint binders such as gums or animal glues, which are both water sensitive. Once I know what affects the original surface, I will be able to think about designing a strategy to reduce darkening while avoiding disruption of the paint layers.

Dry surface cleaning is one of the first methods to test for a water sensitive surface. Cosmetic sponges and soot sponges lifted significant dirt and grime, although the appearance of the figure’s surface was not visibly improved. Water-based solutions and small amounts of solvent were tested in discrete locations to assess their efficacy. Water-based, or aqueous, cleaning solutions can be adjusted with buffers and chelators to more effectively lift dirt and break up staining. Chelators, such as citrate and EDTA (ethylenediaminetetraacetic acid) are complex ions that attach to metal ions, a key component of most types of dirt. A citrate solution at pH 8 was found to be very effective for lifting dirt and staining, but I wanted to minimize surface interaction with water. One method to manipulate these interactions is to work through silicone materials. Silicone gels, such as Velvesil Plus, can from stable emulsions that hold aqueous solutions. Silicone solvents, such as cyclomethicone D4, can saturate surfaces and act as a barrier layer to protect from water.

Testing dry surface cleaning with a cosmetic sponge on the figure’s base.

Testing aqueous cleaning solutions to reduce discoloration with a small cotton swab.

Could this be used as an overall cleaning solution? A larger test area suggested that the combination of materials, when applied carefully with brushes and worked over the surface, lifts dirt without visibly disturbing paint layers. However, the cleaning effect is slightly uneven, which raises concerns about whether this technique will significantly improve visibility and legibility of surfaces. Since this object is a long-term loan from the Philadelphia Museum of Art, continuing discussion with the PMA senior objects conservator, as well as Penn Museum curators, will help clarify these decisions.

In addition to aqueous cleaning methods, I researched the feasibility of laser cleaning. Conservators have successfully employed laser cleaning in many scenarios where discrete layers of soiling need to be removed from surfaces. For Egyptian artifacts, some of the primary challenges include fine control over complex surfaces and slight yellowing after cleaning. While the literature suggests that laser cleaning is unlikely to be the right solution in this scenario, we decided to experiment with a mock-up test panel to gain a sense of the technique’s future applications in the lab. This involved gathering typical Egyptian pigments, including the famous Egyptian blue and green, and mixing appropriate binders to mimic historic surfaces. The panel consists of an animal glue ground with gum arabic paint, coated with an additional layer of mastic varnish for half of the test areas. Mastic, a plant-based resin, is comparable to traditional Egyptian resins such as pistacia. After adding a little bit of “dirt,” a sticky mix of starch powder and pigments, I am ready to start exploring the efficacy of our laser cleaning system for painted surfaces.

Creating a mock-up panel to test laser cleaning on painted surfaces. Materials include Egyptian pigments mixed with gum arabic binder, an animal glue ground, and mastic varnish.

Selected resources:

Korenberg, C., M. Smirniou, K. Birkholzer. 2008. Investigating the use of the Nd:YAG laser to clean ancient Egyptian polychrome artifacts. Lasers in the Conservation of Artworks: 221-226. London: Taylor and Francis Group.

Larochette, Y. 2012. Wolber’s world: A review of a textile wet-cleaning workshop held in Oaxaca, Mexico. Western Association for Art Conservation (WAAC) Newsletter 34(1): 24-26.

Roundhill, L. S. 2004. Conservation treatment considerations for an Egyptian polychrome wood coffin. Objects Specialty Group Postprints 11: 89-102.

Ptah-Sokar-Osiris and Treating Painted Surfaces

Julia Commander is a third-year graduate student in the Winterthur/University of Delaware Program in Art Conservation. She is currently completing a curriculum internship at the Penn Museum.

As a conservation intern working in the Artifact Lab, I was able to go shopping through shelves of Egyptian objects and scope out interesting treatment projects. A painted wood statue, depicting the composite god Ptah-Sokar-Osiris, immediately caught my eye. The figure has intricate painted designs decorating the mummiform figure and its base, as well as gilded details in the face and headdress.

Ptah Sokar Osiris Statue, L-55-29A-C

L-55-29C, detail of paint and gilding

High-status burials in 19th dynasty Egypt often included this type of mummiform statue. Comparable examples of the popular object type exist in collections worldwide, such as the British Museum and the Metropolitan Museum of Art. Common characteristics include carved wood, a preparatory gesso layer, polychrome design, and in some cases, a coating of varnish. Ptah-Sokar-Osiris statues also frequently feature small compartments carved into the wood figure or base. These cavities could contain small papyrus scrolls or textile wrappings. While examining the object with this in mind, I noticed a faint rectangular shape on the reverse of the figure’s head.

X-radiography, a non-destructive imaging technique that helps clarify construction details, was perfectly suited for the question of the compartment. Without disturbing the delicate painted surface, we were able to observe that a rectangular cavity is in fact cut into the head of the figure. Although the cavity appears to be empty, this interesting construction detail is consistent with similar Ptah-Sokar-Osiris figures.

L-55-29A detail (left) and X-radiograph (right). Image captured from 55 kV, 2 mA, and 6 second exposure.

The statue has several condition issues, such as actively flaking paint and significant darkening over the front surface. Additionally, the figure is unable to stand upright in the base, and the components do not fit together securely. Upcoming treatment aims to address these issues, and I will be searching for the right approach to cleaning and consolidation. The complex surface made of wood, gesso, and paint will require detailed testing to find appropriate solutions.

To further investigate painted surfaces and possible coatings, I used multispectral imaging (MSI), which incorporates multiple light sources to reveal details that cannot be seen in visible light. Interesting findings included the presence of Egyptian blue in the figure’s wig and broad collar, as well as the headdress. This pigment shows up in visible-induced infrared luminescence and is easily distinguishable from surrounding pigments.

Detail of multispectral imaging, highlighting Egyptian blue pigment. Normal light (top), visible-induced infrared luminescence (center) with Egyptian blue shown in white, and false color image (bottom) with Egyptian blue shown in red.

Learning more about the object’s structure and surface will help inform treatment decisions about this complex figure. Check back to see what else we learn and how treatment will proceed!

A Complete View and a Complete Treatment: Conservation of the Roman Period Mummy Mask

Update – this post contains outdated language. We no longer use the term “mummy” and instead use “mummified human individuals” to refer to Ancient Egyptian people whose bodies were preserved for the afterlife. To read more about this decision, follow this link.   

After using humidification and four extra hands, the mask is now unfolded! This complete view of the object provides us a wonderful opportunity to look at the materials used in construction and allowed treatment to finally move forward.

Before jumping into treatment, I had the opportunity to perform Multispectral Imaging (MSI) on the mask, allowing us to analyze some of the pigments non-destructively and with great results.

E2462. From left to right: Visible light, Ultraviolet illumination, Visible induced IR luminescence

E2462.
From left to right: Visible light, Ultraviolet illumination, Visible induced IR luminescence

Under ultraviolet illumination, a bright pink fluorescence was visible (middle), indicating the use of a madder lake pigment in the cheeks and to accentuate the face and hands. I also used visible induced IR luminescence to pinpoint the use of Egyptian Blue pigment in the crown, jewelry, and green leaves (right, Egyptian Blue highlighted in pink). This is a material commonly found in Roman period Egyptian artifacts.

In addition to finding out some of the materials used, I also completed full documentation of the object. Although some of the surface is still intact, the paint layer is in poor condition with areas of flaking and powdering. There is also a large loss to the textile along with some smaller tears and holes.

E2462 During treatment detail of flaking paint

E2462 During treatment detail of flaking paint

As my first order of business, the paint needed to be stabilized. This paint, like many other Egyptian painted surfaces, is sensitive to water and adhesives can cause staining and darkening. This meant a lot of testing was required to find the perfect adhesive for the job.

Using both testing panels and small, discrete areas of the surface, I tested adhesives until I found funori, a seaweed-based polysaccharide. This material preserved the matte and light tones of both the paint and ground layers.

Amaris Sturm, summer intern, consolidating surface of E2462

Amaris Sturm, summer intern, consolidating surface of E2462

As treatments usually go, you sometimes get unexpected bumps along the way. As I was consolidating I discovered that the flesh tones in the face and hands were significantly more sensitive to the water-based adhesive. I quickly had to rethink my approach, ultimately using a methyl cellulose in 50:50 ethanol: water for the hands, face, and larger flakes in the yellow framing the face.

Once consolidation was complete, I moved on to the next hurdle: the molded mud plaster mask. A large gap is present between the fragmented mud plaster crown and the textile below. To support the plaster and its mends, I made a removable fill of carved Volara foam and Japanese tissue, all toned with Golden acrylic paints to make the supports more discrete.

Removable fills to support the heavy mud plaster crown in E2462

Removable fills to support the heavy mud plaster crown in E2462

Fragmented, actively shifting, and detached mud plaster was mended with a 40% AYAT in acetone applied by brush and syringe. Unstable and weightbearing cracks and gaps were filled with a 25% AYAT in acetone that was bulked with microballoons and toned with dry pigments. Fill material was applied with syringed, shaped with a brush and wooden skewer, and  smoothed with a little bit of acetone. A thin toning layer of acrylic paint was applied to fills to make them a warmer tone, but still distinguishable from original material.

Filling compromised gaps on E2462

Filling compromised gaps on E2462

And with that, the treatment is complete! The mask is now stable and will be returned to storage safe and sound.

E2462 Before treatment (left) and After treatment (left)

E2462 Before treatment (left) and after treatment (right)

  • Amaris Sturm is a second-year graduate student in the Winterthur/ University of Delaware Program in Art Conservation. She recently completed her summer internship in the Penn Museum’s conservation labs.

Examination and treatment of a cartonnage pectoral

Update – this post contains outdated language. We no longer use the term “mummy” and instead use “mummified human individuals” to refer to Ancient Egyptian people whose bodies were preserved for the afterlife. To read more about this decision, follow this link.   

We have had this object in the collection since 1890:

E352, overall before treatment

E352, overall before treatment

This painted cartonnage pectoral (E352) was made as a covering for the chest of a mummy, and dates to the Ptolemaic Period (ca. 200 BCE). We don’t have the mummy or any other items from the person’s burial, so we don’t know anything about who this belongs to other than that they were buried with this beautiful piece (and likely an equally nice mask, and leg and foot coverings).

This artifact was previously on display in our Secrets and Science gallery and is now in the lab for conservation treatment. It was displayed vertically for over three decades, but since it has come into the lab, we have removed it from the old mount to allow for a full examination, documentation, and treatment.

Multispectral imaging allowed us to identify the Egyptian blue paint used for all of the blue decoration:

An overall image of the pectoral in visible light (left) and a visible-induced IR luminescence image, where the Egyptian blue pigment appears white

An overall image of the pectoral in visible light (left) and a visible-induced IR luminescence image, where the Egyptian blue pigment appears white (right), and everything else is black

We have written about the unique luminescence of Egyptian blue before on this blog, and in the image on the right, above, we can clearly see where it was used to decorate this pectoral.

Conservation treatment so far has included consolidation of the flaking paint with methyl cellulose, carried out under the binocular microscope.

A detail of the pectoral, 7.5X magnification

A detail of the pectoral as viewed through the microscope, 7.5X magnification

I have also been filling small losses with a mixture of Klucel G and glass microballoons, and backing weak areas with Japanese tissue paper.

Here is a link to a mini-slideshow that shows a small section of the cartonnage under 7.5X magnification (the same section seen in the image above). The slidehow shows how I filled a tiny hole with the Klucel mixture, which then allowed me to readhere a tiny fragment of red paint. The change is subtle – see if you can spot where I reattached the paint flake!

Exploring the painted surface of three coffin fragments

Last week, I wrote about x-raying the fragments of a painted wooden coffin, as part of the conservation treatment. The radiographs helped us see what is under the painted surface. We then turned to the painted surface itself. Through cleaning, we revealed how beautiful and well-preserved the decoration is. I described the cleaning process (and linked to a short video showing the process!) in a previous post.

E12617beforeaftercleaning

E12617A-C coffin fragments before (left) and after (right) cleaning

While it was impossible to see the full range of colors on the boards before cleaning, after cleaning we could see that there were several different colors used to decorate the surface, including two different yellows, red, green, black, and paint that appears black but where it is abraded/damaged looks blue. After much experience working on ancient Egyptian painted wooden artifacts, I knew enough to suspect that some of the paint that appears black is actually Egyptian blue.

It appears that there is a lot of black paint here, but not all of this paint was originally black. The yellow arrows point to black paint while the red arrows point to areas that I believe were originally blue.

It appears that there is a lot of black paint here, but not all of this paint was originally black. The yellow arrows point to black paint while the red arrows point to areas that were originally blue.

If you’ve been reading our blog, you are probably very familiar with one of our favorite photography techniques for Egyptian material, visible-induced infrared luminescence imaging. I have written about it previously, where I explain the process and the equipment we use (follow this link to the post).

Sure enough, it worked beautifully to confirm, and to allow us to see the Egyptian blue on this object:

E12617normaIRfalsecolor

Image of the coffin boards in normal light (left), Visible-induced infrared luminescence image (center), False color image (right). Click on the image to see a full-screen version.

All of the darkened/altered Egyptian blue shows up as bright white in the center image above, and the red areas in the false color image on the right help to further visualize where the blue is in relation to the rest of the painted design. Gotta love this technique!

So that’s great for determining the presence and location of Egyptian blue. But what about some of the other colors? I was particularly curious about the two different yellows and the green. In the case of the yellows, are they two different pigments? And as for the green, which pigment(s) were used to produce this color? Without (for the moment – more about that later) knowing the exact time period of this object, I knew there could be at least a couple different options, including Egyptian green (or green frit), and green earth.

To gather more information about these pigments, I carried out portable x-ray fluorescence analysis (pXRF) in select areas on the boards. I collected data from the following areas, marked with colored X’s in the image below:

pXRF analysis locations, with elements detected listed in order of peak height, from large to small

pXRF analysis locations, with elements detected listed in order of relative peak height, from large to small

As you can see, I labeled the image with the findings from the pXRF analysis. It looks like the two different yellows are indeed two different pigments: the darker, more orange-yellow paint contains primarily calcium and iron, suggesting that this is an ochre, while the brighter yellow paint contains calcium, arsenic, and iron. The relatively large amount of arsenic suggests that this yellow was produced using orpiment (arsenic sulfide).

The green paint also contains arsenic, as well as calcium, copper, and iron. So it appears that the green was produced by mixing an arsenic-containing material (orpiment?) with a copper-containing pigment. Due to the lack of any visible-induced IR luminescence in the green areas, I don’t think that these areas could contain any Egyptian blue, so perhaps the green was made by mixing orpiment with Egyptian green. And as you can see, the blue paint does not contain any arsenic, but does contain calcium, copper, and iron, which we expect to find in areas painted with Egyptian blue. Further analysis will be necessary to determine exactly which pigments were used in the yellow and green areas, but we have discovered a lot using these completely non-invasive techniques!

In my next post about this object, I hope to write about the translation and interpretation, for which I’ll need to consult with the museum’s Egyptologists. In the meantime, if you’d like to learn more about green pigments on ancient Egyptian objects, and more applications of multispectral imaging on Egyptian objects, check out this really great video presentation by Kelsey Museum Conservator Carrie Roberts (originally presented at the 2014 ASOR Annual Meeting):

Green Pigments: Exploring Changing in the Egyptian Pigment Palette from the Late to Roman Periods through Multispectral Imaging and Technical Analysis

Multispectral imaging of Wilfred/a’s cartonnage

E12328B_4viewsWhat you see above are 4 different images of our mummy Wilfred/a’s cartonnage. Each image represents a different way of looking at the cartonnage, and assists us in better understanding this object. But what are we seeing in these images, and how did we produce them? (If you have been following this blog, or our museum blog, these types of images may be familiar to you, since we have used these techniques to look at other objects, including a painted wooden shabti box. But every object is different, and in this case, I’ve learned something new that I’ve never seen before, so read on to learn more!)

Let’s start with the image in the upper left – this is easy.

E12328B_visible01_compressed

Visible image. Captured with a Nikon D5200, modified by replacing the hot mirror filter with a glass custom full spectrum filter, with a B+W UV-IR-cut filter & incandescent photo light source.

This is a photograph taken in normal (visible) light with a digital camera. This image represents what you see when you look at the object here in the Artifact Lab. We see that the surface of the cartonnage has a design painted in many different colors, and that there are some residues on the painted surface in areas. There is a lot that we can learn about this object just by looking at it in visible light, but what we cannot do is confidently identify the pigments used. So in this case, multispectral imaging comes in very handy. Let’s take a look at the next image.

E12328B_IR01_compressed

Visible induced IR luminescence image. Captured with Nikon D5200 modified full spectrum camera, #87C filter, Crimescope 600nm light source.

This is an image of the exact same view of the object, but it was captured using our modified digital camera with a #87C IR filter, using our SPEX Mimi Crimescope with the 600nm filter as a light source. With this technique, we can clearly identify that Egyptian blue was used in the areas that appear bright white, because these areas are showing visible-induced IR luminescence (in other words, they emit infrared light when excited with visible light). No other pigment used by the ancient Egyptians has this property, so we can say with certainty that these areas are painted with Egyptian blue. To better visualize these areas (since the rest of the image is nearly black) we can use the image captured in visible light and the above image to create a false color image.

False color image of the cartonnage created in Photoshop, where the areas painted with Egyptian blue appear red.

False color image of the cartonnage created in Photoshop, where the areas painted with Egyptian blue appear red.

The false color image shows us the luminescent (Egyptian blue) areas in red. If you look closely, you’ll be able to see that the red areas are slightly shifted, due to the fact that we probably bumped the camera in between shots. But you get the idea.

Finally, I wanted to see what we could learn about the cartonnage by looking at it under other wavelengths of light with the Crimescope. I was expecting that we’d probably be able to better visualize the old adhesive used to join the cartonnage fragments in the past, and maybe better understand the residues on the surface. But when we looked at it with the 300-400nm filter (with a peak emission of 365nm), this is what we saw:

UV visible fluorescence image, captured with a Nikon D5200 modified full spectrum camera with B+W UV-IR-cut filter, using the Mini Crimescope 300-400nm filter.

UV visible fluorescence image. Captured with a Nikon D5200 modified full spectrum camera with B+W UV-IR-cut filter, using the Mini Crimescope 300-400nm filter.

In this image, the areas that stand out the most are the areas fluorescing a bright orange-pink color, which appear pink in visible light. I had never seen this before and wasn’t exactly sure what this meant, but after looking into it a bit, I believe that this fluorescence indicates that the pink areas were painted with madder, a dyestuff obtained from the roots of the madder plant. Madder has been identified as being used in ancient Egypt to create pink pigments for painting, and is known for having a characteristic pinkish-orange UV fluorescence, which is how I would characterize what we’re seeing in the above image. There are other ways we could try to confirm this, but this was an exciting, and unexpected observation!

* Special thanks to conservation intern Yan Ling and Conservator Tessa de Alarcon for their help with capturing and processing these images.

Glowing in the dark: multispectral imaging and Egyptian blue

There is something I’ve mentioned before on this blog, but never actually shown, and that is the ability to “see” Egyptian blue on objects using multispectral imaging. On many objects Egyptian blue is very well-preserved, so there is no need for special examination techniques in order to spot it. But there are cases in which being able to accurately identify this pigment is important. Sometimes Egyptian blue deteriorates either by changing color (to green or black) or by becoming lost altogether, making it difficult to know which areas may have originally been blue, or if blue was used at all.

And then there are objects like this one:

Front view of the shabti box in normal lighting conditions

Front view of the shabti box in normal lighting conditions

You’ve seen it before, it’s our painted wooden shabti box. I have been working on the treatment of this box for awhile now, mostly to stabilize the flaking paint and varnish. And this thick, orange-yellow varnish, which we believe is original, and is pistacia resin, makes it difficult to see the painted surface, both the details and the colors. While I could see that there is some green and possibly blue paint on this box, between deterioration of the paint and/or pigment, and the thick application of pistacia resin, I couldn’t say for sure which areas may have originally been painted blue…until now…

Taking advantage of the fact that Egyptian blue has luminescent properties when illuminated with visible light and captured in infrared, we can detect where Egyptian blue was applied. And wow, look at these results:

Visible-induced IR luminescence image of the shabti box. Light source: SPEX Mini Crimescope with 600nm band-pass filter. Captured with a Nikon D5200 modified camera with an IR 87C filter.

Visible-induced IR luminescence image of the shabti box. Light source: SPEX Mini Crimescope with 600nm band pass filter. Captured with a Nikon D5200 modified camera with an IR 87C filter.

This is the same surface of the shabti box seen in the first photo, but zoomed in a bit, and taken under different lighting conditions and captured with a different camera. The areas that appear white are where Egyptian blue was applied. Because everything else pretty much disappears on the box in this image, to better visualize where the Egyptian blue is in relation to other details, we created a false-color image in Photoshop:

False color image of the shabti box. The areas painted with Egyptian blue appear red.

False color image of the shabti box. The areas painted with Egyptian blue appear red.

In this false color image, the areas that appear red are where the Egyptian blue was applied. It’s not perfect (you can see that the bands in the hair of the figure on the right don’t really show up) but we could play around with the photographs a bit to improve this.

We did this imaging on all surfaces of the box, and on the box lids. Here is a regular photo, a visible-induced IR luminescence photo, and a false color image of one of the box lids, also showing lots of Egyptian blue:

Shabti box lid, normal light

Shabti box lid, normal light

Visible-induced IR luminescence photograph

Visible-induced IR luminescence photograph (areas in white = Egyptian blue)

False color image (areas in red = Egyptian blue)

False color image (areas in red = Egyptian blue)

You can use any regular/visible light source to produce the luminescence, but in this case, we used our fancy-schmancy new Mini Crimescope, which was developed for forensic work, but is useful to us because it allows us to examine objects under specific wavelengths of UV and visible light. We found that using a peak emission 600nm light source worked best for the excitation of the Egyptian blue.

In order to “see” the luminescence, we have to capture images using a modified digital camera, with an 87C IR filter.

In summary, we’re having lots of fun with our new equipment, and finding that these Egyptian objects are perfect subjects for learning how to use the Crimescope and the modified camera, because they produce such great, dramatic images.