Photographing Glass: Revisiting the Morgan Cup 30 Years On

I recently had the opportunity to photograph one of my favorite pieces from our collection, the Morgan Cup (52.1.93), which is a beautiful example of Roman cameo glass. The cup was once in the collection of J. Pierpont Morgan, from whom it got its name, and was given to The Corning Museum of Glass in 1952 by Arthur A. Houghton, Jr. For more information on the Morgan Cup, read this detailed history by David Whitehouse, former director of the Museum.

The Morgan Cup (52.1.93).

The last time the Morgan Cup was fully photographed was in 1990, six years before I started at the Museum, when it was captured on 4×5 transparency film. The transparencies were later scanned, but technology has advanced considerably since that time and I was excited to see how well the cup could be captured with the highly advanced digital equipment we have today—both for detail and color fidelity.

Over the years I have had a few opportunities to examine the cup closely, and even did some photography for scholars looking for clues to how the cup was made. However, there was never enough time to do full photography because of pressure to limit the time it was not on display. As a result, I relished the rare opportunity to spend time with this incredible object, examine it closely, and explore how it reacts to light. I like to wonder what its makers would have thought if they could somehow have imagined me in a darkened studio 2000 years later carefully adjusting the lighting on their creation in an attempt to best reveal their artistry.

The opportunity to photograph the Morgan Cup arose when the San Antonio Museum of Art submitted a request to borrow the cup for their major exhibition of art from the early Roman empire titled Art, Nature, and Myth in Ancient Rome.

When CMoG receives a loan request like this, the prospective loan object is first thoroughly photographed to document its condition. A conservator then closely examines the object and uses the images to prepare a detailed condition report as well as an assessment of whether or not the piece can safely travel.

Animated GIF showing all exterior sides of the Morgan Cup.

We capture at least four view angles around the object, as well as top and bottom views. Details of individual areas identified by the conservator are also captured. A color target is included in the image to verify accurate color and to provide a point of comparison for the future.

Condition documentation photography, as the term suggests, documents the physical condition of the object. That approach is different from publication photography, which attempts to beautifully capture the object and its interaction with light, but there are core similarities. For both types, we use calibrated cameras and create color profiles for each combination of lighting, camera, and lens. We use integrated color management to both accurately capture color and to maintain that accuracy through our post-capture workflow all the way to the final digital files. The difference between the two approaches comes down to the use of different lighting techniques to achieve different ends.

For the condition documentation images, two large soft lights were positioned at 45° angles from the object for flat, even lighting, and the object was captured in direct profile on a neutral gray background.

For the publication images, the cup was photographed on a black velvet background to enhance contrast, and from a slightly higher angle to show the shape and volume of the cup. A soft light is positioned overhead and reflector cards are carefully placed to bounce light onto the surface to reveal form and detail. In addition, a small source hard light is positioned overhead and slightly out front for directional light. (For more information on using reflectors, check out this older blog.)

The difference between the two types of lighting can be seen clearly in these detail views. Both images have fine detail and accurate color and are equally successful for their intended use. In the publication image on the left, the combination of directional, reflected, and transmitted light renders the figure and drapery with more volume, creates a subtle range of contrast from highlight to shadow, and reveals greater variation in the blue glass. In the condition documentation image on the right, the flat light renders all detail with equal importance without emphasis on volume, shape, or form; this version is ideal for an analysis of the surface condition and the repaired crack (bottom right of image).

As you may have noticed, the angle and direction of light also have an effect on how the color of the glass appears, even when using the same color-profiled lighting. Glass reacts to the angle, intensity, and direction of light with differing amounts of transmission, reflectance, and refraction, and the resulting differences in color can be subtle or dramatic. With the detail images of the cup above, you should notice a shift in the blue glass due to the changing balance of reflected and transmitted light. Likewise, the white glass changes with directional vs. flat light, and depending on how much blue glass shows through it. Historically, the limits of the medium of film and the effects of processing added even more variables.

In 1990, when the Morgan Cup was last fully photographed, it was captured on color transparency film. In general terms, the ability of color film to accurately capture the particular frequencies of the deep blue, almost cobalt, glass in the Morgan Cup was subject to many variables such as the type of lighting, exposure time, and the particular dyes in the film emulsion itself. The necessary chemical processing required added its own color-shifting variables, as did the subsequent scanning of the transparencies. The adoption of consistent color calibration, profiling, and integrated color management in the imaging industry—especially as driven by the museum and cultural heritage imaging community, allows us to capture the color much more accurately today. (True cobalt blue is still outside the RGB color gamut of digital capture, but that’s another topic.)

Clear differences in color can be seen between the 1990 film capture on the left and the recent digital capture on the right.

Another advantage of digital capture is the ability to use a technique called focus stacking to capture images with a greater range of sharp focus, which is particularly useful for close-up detail views. Without getting too technical, in a traditional single-shot exposure, greater depth of field (range of image in focus) can be achieved by “stopping down” to a smaller aperture in the lens. However, stopping down comes at the cost of overall sharpness. The better the lens, the less the loss of sharpness, but all lenses have an optimal sharpness near the middle of their aperture range. With focus stacking, we can set the aperture for peak sharpness, take multiple images at different focal points, and then use software to combine the images into one that is sharp throughout the range.

Multiple images are taken at progressively deeper focal points. The right image shows the software (ZereneStacker) processing the separate images into one combined image.

Animated GIF showing the different stages of focus.

Focus stacking makes it possible to get a tremendous amount of depth in focus, as with this base view of the Morgan Cup. With a single capture and point of focus, I would have had to either let most of the object go out of focus or move the camera back and make the object much smaller in the frame in order to carry more depth.

Focus stacking helps make macro photography, which plays an important role in revealing information about an object, more effective. For example, the concentric toolmarks captured crisply in the image above give valuable clues to how this object was made. The way glass reveals marks of its making through interaction with light is one of the things I find most satisfying about photographing glass. The direction of a light, the angle of a reflector, or the adjustment of lighting contrast in the background can make previously invisible toolmarks, chill patterns, coldworking, distorted internal bubbles, or even traces of long-lost gilding visible.

Photographing the Morgan Cup gave me the opportunity to document its condition thoroughly and capture it with accurate color and in a higher level of detail than previously existed. It also felt like an opportunity to just spend quiet, reverent time with an amazing object I usually only get to see in a display case.

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