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Photographic Techniques
used when recording petrogyphs on Ometepe Island

by James Martin

Petroglyphs can be maddeningly difficult to photograph. They are almost always located in a remote area. Trudging to them with the 100 pounds or so of equipment that might be required to light and photograph them properly is generally inadvisable, especially in the tropics in summer. In any case, one usually arrives at a time of day when the "natural" light, so poetically described and utilized by Ansel Adams, is more of a hindrance than help. The engraved or pecked lines may be so shallow as to be almost invisible. Erosion can make any petroglyph faint enough to be missed by the casual observer. So what's an archaeologist with a bad back, arriving at an inopportune moment with rudimentary equipment and many petroglyphs to record, gonna do?

A little background is in order. On Ometepe Island, the depth of the engraved lines on recorded petroglyphs varies from immeasurably shallow to around three centimeters. As an example for our discussion on how to photograph difficult situations, let's use the petroglyph R29-P1 from N-RIO-3, the one that's used as the background for the Field Notes page.

This petroglyph is found on a nearly vertical slab of basalt bedrock. The panel measures 210cm high by 300 cm wide. Another slab of basalt immediately adjacent and at a right angle to R29 contains another human figure similar to the 5 found in R29. Together they form what may be described as a family, if archaeologists were allowed to make wild and unwarranted judgments.

Here's the finished photo. In this case we were unable to block the background light completely, so there are some deep shadows on the face of the petroglyph.

Still, the reflector brought out details that even the sketcher hadn't seen before.

The first step taken in recording and petroglyph was to draw the entire panel and fill in a petroglyph form. On petroglyphs as faint as this one, the drawing was often done by a sort of Braille technique, with the recorder tracing nearly invisible grooves with the tip of her fingers. Once this task was completed, the photographer, namely me, would saunter over and take a photo using the following technique.

First, the direction of the light is determined, then a small, portable reflector is set up to cast light at an oblique angle over the petroglyph surface. If warranted, the direct sunlight striking the petroglyph surface is blocked by tarp, so only the reflected light remains. This often brings out enough luminance variation over the rock surface that the sketcher will see even more detail that even a close examination by sight and touch had previously missed. Changing the angle of the reflector only slightly often brings out additional detail. Several photographic exposures are made, often with slight variations of reflector angle.

So here's the basic setup. A portable reflector is used to reflect available light so that the grooves in the petroglyph are in deep shadow.

Rarely, however, does a petroglyph appear on the porch of a 19th century hacienda. But that's the problem in Nicaragua and around the world these days, the smaller finds are quite often carted off for souvenirs.

Back at home, the black and white film is developed to add about one paper grade of contrast by increasing development time by about 20%. Then the photographs are scanned into Photoshop. Here the contrast can be enhanced, the shadows cast in the grooves can be deepened and the parallax error that occurs when the camera lens cannot be brought completely parallel with the rock face can be corrected using data extracted from the drawing.

If the rock face has a curvature that makes it difficult to light, separate exposures can be taken with the light corrected for different areas of the petroglyph face and the photographs layered in Photoshop. Then each layer can be combined in a way that utilizes the best lit areas from each layer to produce a final file for printing.

About That Reflector!

The reflector shown in these pages is a Litedisc produced by Photoflex. It expands to 32" and folds for storage and transport to about 12" in diameter. It's a bit tricky to fold up, but once you get the hang of it the whole process looks like magic. And folding the reflector for storage was a source of endless fascination for the local kids!

The reflectors can be purchased with different coatings on each side. Ours is silver on one side for reflection and black on the other to hold light back from an object.

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Papers: The Petroglyphs of Ometepe Island by Suzanne Baker