Cultural Heritage Imaging

June 9, 2011, 10:14 pm
Filed under: Conferences, Training

June 8, 2011

Buzzed at AIC

At the recent annual meeting of the American Institute for Conservation (AIC) in Philadelphia, I was happy to see both past and future participants in the IMLS-sponsored CHI RTI training session program. I had to break the news to some interested parties that the sessions at the Worcester Art Museum and at the San Francisco Museum of Modern Art are already filled (with waiting lists) – but a few openings remain (apply here) in the sessions scheduled for the Smithsonian’s Museum Conservation Institute and the Indianapolis Museum of Art. Since AIC, several spots have already been taken.

Of course, conservators always want more visual information, and have been quick to understand the benefits of RTI for their work. Once conservators attend a CHI training session, RTI adoption spreads throughout the conservation community. At AIC, I heard several tales of conservators reaching out to their curatorial colleagues, presenting the extremely detailed technical art historical information to be gained from RTI. Curators were impressed! The ability to acquire this kind of detail is one of the hallmarks of RTI – in fact, in CHI’s Kress video Debbie Evans (paper conservator, Fine Arts Museums of San Francisco) mentions that RTI can allow the conservator to provide this important, detailed information to the curator. We look forward to more wonderful conservator/curator interactions!

By Elizabeth Peña

Comments Off on RTI BUZZ AT AIC

Documenting a Reverse Glass Painting using Reflectance Transformation Imaging
April 1, 2011, 9:21 pm
Filed under: Commentary, Guest Blogger

By Guest Bloggers:

Golya Mirderikvand (Art Conservation, Queen’s University) and George Bevan (Classics, Queen’s University)

In the fall of 2010 a Master of Art Conservation Student, Paintings Stream, at Queen’s University, Golya Mirderikvand was confronted with a unique challenge: how to document a reverse glass painting before beginning treatment. From the recto the painting is convex with the paint being applied on the concave verso. Because the flaking and delamination of the paint was on the concave side, it was difficult to produce raking-light shots that would fully reveal the variation in texture without creating internal shadows that obscured the surface. Reflectance Transformation Imaging (RTI), which had already been extensively used by George Bevan in Classics, was then employed as the ideal way to document such a work.

Figure 1: House next to Stream, Recto

First some background on the type of work in question. Reverse glass paintings, or more commonly known by their German name Hinterglasmalerei, refer to the decoration of glass by painting or engraving metallic foil on the back of a glass panel.  Reverse glass paintings have a rich history with distinct variations in styles and techniques apparent from different periods.  Although their exact origins in Europe are uncertain, it is generally agreed upon that they were popularized in the 14th century, with the oldest surviving reverse glass paintings dating from the second half of the 13th century.

Figure 2: House next to Stream, Verso. Imaged under normal illumination

Paintings executed on glass panels are inherently fragile and susceptible to deterioration since they are not fired to allow the paint to become fused with the glass.  The primary mechanism of deterioration of reverse glass paintings is the detachment of paint films to the non-porous glass substrate. It has been speculated that a lack of proper preparation of the glass support in order to provide a better tooth, or a lack of application of a priming layer, or a combination of both, can lead to the delamination of the paint layers.  Other possible reasons of detachment could be as a result of condensation of moisture on the surface of glass, causing the paint films to release.  Internal and external factors contributing to the creation of interlayer shear forces can also lead to paint delamination.  This can commonly occur as a result of any backings or adhesives in direct contact with the paint layer from the back, or changes in relative humidity causing contraction and expansion within the paint layers.

Figure 3: House next to Stream, Verso. Imaged using RTI.

Figure 4: House next to Stream, Verso. Detail of upper left area, with normal illumination. Delamination and Blind Cleavages are identified within red ellipses.

Figure 5: House next to Stream, Verso. Detail of upper left area with RTI. Delamination and Blind Cleavages are identified within red ellipses

IMLS Sponsored 4-Day RTI Training at NYU
March 24, 2011, 11:18 pm
Filed under: On Location, Training | Tags: ,

Well, I love NY too.

In late March 2011, Mark Mudge, Carla Schroer, and Marlin Lum traveled to take a bite of the Big Apple and at its core was a 4-day RTI Training Session at the NYU Institute of Fine Arts Conservation Center. There, brilliant students and museum professionals participated in a 4-day hands-on RTI training. Each student learned how to capture, process, and view a Reflectance Transformation Image.

If you don’t know what a “RTI” is, read this, and you’ll have a better idea why it’s important:

“Reflectance Transformation Imaging (RTI) is a technology that has the potential to revolutionize documentation, treatment, and research of museum collections, while also promoting the integration of interactive images into the visitor experience. RTI enables museum professionals to examine an object’s very fine surface details using basic digital camera equipment and a few small additional tools.”

yup, we're capturing UV/IR RTis!

This training at NYU was partially sponsored by the Institute of Museum and Library Services. With the assistance of their funding, we are delivering 21st-century computational imaging tools into the hands of professionals who can make a substantial difference.


Brilliant Students(.)

As human beings on this earth for such a short time, we are striving to actually ‘make difference’ in people’s lives and in their careers. We want to make their work more meaningful and concrete. The final product is not just an interactive lighting map, but much more: knowledge, insight, value, and scholarly information, revealed by the artwork itself.

While on location at NYU, one of our students made an important comment. He pointed to the corner of the photo studio and said, “… that space there, that’s where, just last year, the photo enlargers were — we recently had them permanently removed.” (insert … silence, then echo laughter in a marble hallway)

RTI setup

NYU students during an RTI capture

That said, we’re moving right along into 21st-century computational imaging tools … we can now know more about our artwork than ever before.

A special thank you to NYU and *Hannelore Roemich.

Thanks for reading.

Marlin Lum
Imaging Director
Cultural Heritage Imaging.


PS: If you want to learn how to capture, process, and view RTI lighting maps, apply to the free IMLS-sponsored training sessions. Click here to get the details.


Discoveries made at every viewing!

Free IMLS Sponsored 4-Day RTI Training Sessions
March 23, 2011, 10:11 pm
Filed under: Training, Uncategorized, Workshops

“21st-Century Museum Professionals Grant Program”

Institute of Museum and Library Services
National Leadership Grant Project

Thanks to a generous grant from the Institute of Museum and Library Services 21st Century Museum Professionals program, CHI is pleased to present a series of FREE training sessions in Reflectance Transformation Imaging (RTI), graciously hosted by the following institutions:

Worcester Art Museum: July 11-14, 2011

San Francisco Museum of Art: Aug 15-18, 2011
Smithsonian Museum Conservation Institute: Mar 5-8, 2012
Indianapolis Museum of Art: Sept 10-13, 2012

Learn More. Space is Limited. Apply NOW.


4-Day RTI Training at the Metropolitan Museum of Art
January 5, 2011, 7:37 pm
Filed under: Commentary, Training
The Met

Metropolitan Museum of Art

In mid-December, we braved the cold and headed to the Big Apple for a 4-day RTI Training session at the Metropolitan Museum of Art, to be followed by a day of consulting on special projects. We were all delighted to be there and to enjoy the magic of Christmas-time in New York!  And of course, it was a true privilege to be welcomed by the Met. Thanks to Larry Becker of the Objects Conservation Department for inviting us, and thanks to Carolyn Riccardelli and Ashira Loike for making all the arrangements and plans.

Larry Becker and the OCD (includes CHI)

Day 01

We began our Monday with introductory RTI lectures and our favorite fish fossil demo for an audience of nearly 50 museum employees! After lunch, a core group of 16 Met staff joined us for a hands-on RTI shoot. It was interesting to hear about each participant’s interest in RTI – examining armature marks on a bronze sculpture, looking at scratches on copper plates, searching for fugitive paint on a wooden object, and other great research questions. For the afternoon RTI shoot, an Islamic writing box was selected. The goal was to establish a condition image, with close-ups to examine construction details and to try to determine if the white inlay displays characteristics of bone or ivory.

Day 02

The following morning, we processed the writing box data set, creating an RTI.  An interesting observation: we need an RTI databank, so that we know what ivory and bone are “supposed” to look like in an RTI image. In the afternoon, we headed to the objects conservation department and divided into two RTI capture groups and one processing group. Despite some technical glitches with the Met’s Nikon camera and new computer, a number of successful RTIs were created, from an enameled plaque to an engraved lead ingot.  By the end of the day, the conservators seemed encouraged that they could really do this — and, Anna Serotta and Ashira managed to get the Nikon and computer up and running.

Day 03

One of Wednesday’s highlights was a lecture by CHI partner Dr. Szymon Rusinkiewicz of Princeton University. The audience seemed particularly interested in Szymon’s description of using computational photography to help mend a severely fragmented fresco. Szymon also discussed some of his ongoing collaborative work with CHI, including the research and development of algorithmic rendering using RTI capture data.

Most of the rest of Wednesday was a three-ring circus (in a good way) – three RTI capture stations were established, and conservators busily shot image after image. The intention was to provide practice with large and/or upright objects. Everyone seemed to be focused and engaged in the process. It was empowering to see Met staff taking over after only a few days of instruction. RTI = Reflection Transformation Imaging = Real Teamwork Involved!

Day 04

Thursday’s morning lecture covered post-processing issues, using highlight maps to show the actual light positions that were captured. The class considered different and better ways to gain even higher quality results. Then, RTI capture and processing moved back to the Objects Conservation Department.  A bronze Bodhisattva, an African mask, and a historic violin were imaged – the conservators are still pondering the results.

Carla teaching

Processing and viewing RTI files are easy, but it takes a good amount of concentration. Carla in teaching mode.

The class ended with a “show & tell”, and we got to see each other’s results! Our immediate feedback is that the conservators really took to the new technology and that they enjoyed working together as a team. From CHI’s perspective, we were gratified, pleased, happy, and exhausted!

Day 05 – Day of Consulting

The CHI team did return to the Met on Friday for a day of special consulting. Mark Mudge and Marlin Lum worked with Anna, Carolyn, and Ashira to document a relief in the Tomb of Perneb. Mark helped Debbie Schorsch and Daniel Hansdorf with a microscopy set up to shoot an RTI of a metal fragment – they were delighted to see toolmaker’s punch marks! Meanwhile, Carla Schroer used her software expertise to concentrate on RTI post-processing and viewing support.

After an eventful and productive week at the Met, the CHI team returned to California feeling like we’d not only worked with new colleagues, but made new friends.

By Elizabeth Peña and Marlin Lum

Japanese woodblock prints and RTI

By Guest Blogger:

Susan Grinols, FAMSF, Director of Photo Services and Imaging

You wouldn’t necessarily think you needed anything but your own eyes to appreciate the details of a Japanese woodblock print. After all, how much texture is there in a thin piece of paper? It turns out – quite a bit. While working with CHI on the Samuel H. Kress Foundation Grant we proved to ourselves that RTI is adept at revealing hidden textures in these artworks. We did this by photographing one of our Hirosada woodblock prints:

Konishi Hirosada woodblock print

Konishi Hirosada woodblock print

  • Konishi Hirosada, Japanese active 1819-1864
  • The Osaka Actor Mimasu Daigorō IV as Kan Shōjō in the Play “Sugawara denju tenarai kagami” at the Naka Theater
  • 1851
  • Color woodcut with metallic pigments, “lacquer,” and embossing
  • Image: 24.5 x 18.8 cm (9 5/8 x 7 3/8 in.)
  • Museum purchase, Achenbach Foundation for Graphic Arts Endowment Fund, 1976.1.359

We were amazed to see that the woodblock carver accentuated the actor’s expression in this print through embossing. He also produced subtle and not so subtle textures in the actor’s kimono. These details really come out with RTI.

Konishi Hirosada Woodblock print

Normal / Specular viewing

When exhibiting our prints we frame them behind plexiglas and limit their exposure to damaging light by keeping the light levels low. This combination sometimes makes it difficult for people to see all of the artwork’s subtle textures.

To give our visitors a richer experience of the Hirosada print we decided to include its PTM in the galleries while the artwork was on display in our exhibition Japanesque.

Unfortunately we didn’t have enough time to get the RTI viewer onto a kiosk before Japanesque’s opening so we decided to make a movie of the Hirosada PTM using Screen Flow and iMovie. BTW, a BIG THANK YOU goes out to the CHI team for the beautiful imagery we used in the movie, and also to Michael Ashley for his technical movie making expertise, and to Mark Mudge and Carla Schroer for their help in writing the gallery label.

The end result is a short movie with detailed imagery of the artwork. The best part is that the movie is being displayed on a 46” flat panel screen with the artwork hung close by, making it convenient for our visitors to compare the RTI results with the actual artwork.

Woodblock prints are the result of collaboration between the artist, the carver and the printer. Using RTI technology, our visitors are able to get a real appreciation for their artistry.

October 7, 2010, 7:56 pm
Filed under: Commentary, Conferences, Guest Blogger

A couple of weeks ago Carla Schroer conducted a workshop for a selected group of members of the Western Association for Art Conservation (WAAC) and members of cultural institutions in the Portland, OR area. The workshop was conducted at the beautifully restored and technologically advanced White Stag building of the University of Oregon, Portland. The title of the workshop was Digital Imaging Techniques for Conservation & Education. The three hour workshop was divided in two main sessions. In the first session, Carla lecture, via presentations, on the development and implementation of Reflectance Transformation Imaging (RTI) in the conservation field and cultural heritage institutions.

Carla in teaching mode.

Carla brought a small fossil with her to be photographed. She explained the minimum equipment requirements and recommendations for successful setups for different size and types of objects. Once all the mechanics where explained Carla, a volunteer from the group, and my self proceeded to capture the object with 24 images each with a different lighting position. She followed by explaining the postproduction steps to build the final RTI image as well as the use of available viewers for these images. She also demonstrated some of the computational enhancements that could be applied to the images and the amazing amount of information that can be obtained in this way. The day ended with a great Q&A session that really brought home many of the concepts that Carla had touch upon during the day finalizing a really informative workshop.

On a personal note I am very happy to have had the opportunity to assist Carla with the practical aspect of the workshop, but even more happy that Carla came to the meeting and that she was able to mingle and meet many of the members of this wonderful WAAC organization. Wishing a long lasting partnership and collaboration among the two institutions I remain thankful.

Yosi Pozeilov
Sr. Conservation Photographer
Conservation Center, LACMA

VAST 2010 at the Ecole du Louvre, Paris
October 4, 2010, 7:54 pm
Filed under: Commentary, Conferences, On Location, Technology, Workshops

The Virutal Reality, Archaeology and Cultural Heritage (VAST) conference was great for us, and we are still enjoying being in Paris. This is a small focused conference with usually about 100 people in attendance. We put together a full day tutorial at the start of the conference with some of our favorite collaborators, and it was great to get this group together in person. We covered a lot of ground in a day with a nice mix of practical and theoretical material.

Carla setting up a demo during the tutorial

The rest of the conference was really good. I always enjoy the chance to catch up with various colleagues and friends, meet new folks working in this field, and see what other folks are up to. VAST is usually more on the computer science side of things, but there were a number of museum folks as well as archaeologists in attendance. There are always lively and sometimes controversial discussions, and this year lived up to that standard. Of great interest to me were the papers and discussions around how digital representations can track and reflect their true digital provenance from acquisition through to the finished process.

Mark and Carla in front of the Ecole du Louvre - site for the conference

I particularly appreciated a discussion with Holly Rushmeier from Yale University about what we mean by accuracy, high resolution, and quality in general? In particular what is even measurable, and how should we be measuring and recording it? Holly agreed that this is an area that needs some attention, and it will take the work of multiple institutions working together to come to any guidelines.

Having a chance to talk to Martin Doerr about mapping the digital provenance data to the CIDOC CRM always requires having your thinking cap on, but it’s so worth it. There were many other great people in attendance, interesting papers, and good food, wine and conversation. I look forward to next year when VAST is combined with VSMM (International Society on Virtual Systems and Multi-Media) in Alexandria, Egypt.

July 23, 2010, 11:06 pm
Filed under: On Location, Training | Tags: , , , ,

By Elizabeth Peña

Last week, the CHI team headed to the Big Apple to deliver a custom-built lighting array to the Museum of Modern Art Conservation Department, and to conduct a 4-day training session with MoMA conservators and guests. It was wonderful to work with such an accomplished, collegial group whose insights inspired us every step of the way. By the end of the week, the group had accomplished RTI’s ranging from a Jeff Koons basketball to a Brancusi sculpture, as well as paintings by Gottlieb and Gorky, a Schwitters collage, and several photographs for an important photograph characterization study. Many thanks to Jim Coddington and everyone at MoMA for their generous hospitality. We look forward to continuing to work with the MoMA staff as they begin to incorporate RTI into their work.


Clockwise from left: Linda Zycherman, Corey Toler-Franklin (Princeton), Mark Mudge (CHI), Szymon Rusinkeiwicz (Princeton), Carla Schroer (CHI), Rick Johnson (Cornell), Marlin Lum (CHI), Mary McGinn (Winterthur), Chris McGlinchy, Robert Kastler, Paul Messier (Paul Messier LLC), Dan Kushel (Buffalo State), Michael Duffy, Lee Ann Daffner, Jim Coddington. Not pictured: Scott Gerson, Ana Martins, Cindy Albertson, Elizabeth Peña (CHI)

Flexible Solutions for RTI
June 8, 2010, 6:07 pm
Filed under: Commentary, Guest Blogger

CHI Blog Post—May 2010

By Guest Blogger E. Keats Webb

Senior Conservator, Melvin Wachowiak, and I have continued using Reflectance Transformation Imaging (RTI) on a regular basis at Smithsonian’s Museum Conservation Institute aiding in the research and preservation of the collections both within the Smithsonian and outside. We have found the technique to be a great indicator of the condition of objects as seen in the imaging of a 2×2.5” daguerreotype. A daguerreotype is one of the earliest photographic processes that formed an image on a silver coated copper plate. The highly reflective and relatively flat surface proved to be an ideal candidate for the RTI process. Using a 21-megapixel full-frame sensor, our final RTI file revealed the detailed information of polish marks and scratches on the metal surface and allowed very close examination due to the high resolution.

The image acquisition for the RTI process has definitely been an adventure of trial and error. When initially imaging the daguerreotype, we ran into issues with flare on the object. We crafted a homemade snoot from cardstock, black velvet and rubber bands, which quickly solved the problem and generated a beautiful final RTI file. This was not our first run-in with stray light. Working with larger objects on the wall and even smaller objects on the copy stand, we have experienced stray light from surroundings including the floor and ceiling tiles and the copy stand post, issues that we remedied with available non-reflective diffuse material like dark moving blankets or scrap velvet. A final example of our adventures of image acquisition includes a human skull and a ring flash. We were losing information to shadows in the roof of the mouth of a skull while imaging the gold filings in the teeth. To resolve this loss of information we used a (stationary) ring flash during the image acquisition in addition to the standard repositioned light source. Before processing the files in RTI Builder, we batch-edited the files removing the ring flash highlight on the reference spheres, which produced a successful final RTI file.

In our image acquisition explorations, we have adopted a creative process of trial and error to our RTI workflow that can incorporate crafting homemade devices and using available materials to remedy unexpected hurdles.