Wednesday, October 28, 2009


Back about 30 years or so rock art recording was much less sophisticated and technical than it has become since. It was also less effective and often caused serious damage to the rock surface. Rubbings required pressure on the rock face and often bled chemicals through to the rock surface. Photographic recording was often done with materials applied to the petroglyph to enhance the contrast in the photo. The most egregious example of that I know of is in the canyon of the Purgatoire River in southeastern Colorado where a line of petroglyph characters was carefully painted in with aluminum paint to show up well in photos. One very popular technique was the creation of a silicon latex or rubber peel, or mold taken by painting the liquid latex on the surface. This was peeled off the rock after curing and then used as a mold to make casts of the petroglyph with plaster. One problem with this technique is that it all too often pulled portions of the rock surface away too, irreparably damaging the petroglyph. As somewhat of an aside, I have seen one site where some moron tried to make a plaster cast of a petroglyph, and didn’t even know enough to use a release agent on the rock surface. The plaster stuck, of course, and was then obviously chipped off by hand with results you can imagine.

Fig. 1 - Scan of shield figure petroglyph,
input on computer screen.
Photo: Tim Urbaniak.

I received some truly exciting information and pictures from Tim Urbaniak at Montana State University in Billings, Montana, about a new technique of three dimensional recording of petroglyphs that does not require any touching of the rock surface, let alone adding material to it. Tim is a doctoral student, and has spent the last decade exploring applications of technology to archaeology and historic studies as the director of the MSU Billings Archaeology Field Team.
The recording was done with a Polhemus FastSCAN Scorpion unit. Tim has found it to be accurate to about 1/3 millimeter. A handheld unit contains two cameras and a laser unit which sweeps the rock face when the trigger is pulled while the cameras record the resulting sweep from two different angles. The resulting signals are analyzed with software which provides a detailed record of the distance to any point on the rock surface. Figure 1 shows the resulting scan pattern on the computer monitor screen. The data can then be used to generate a three dimensional image of the surface in the computer as shown in Figure 2.

Fig. 2 - Scan data result processed, shown
on computer screen. Photo: Tim Urbaniak.
The best part comes with the final option offered by this digital technique. The computer can also use this data to recreate a three dimensional facsimile of the surface using rapid prototyping techniques. Figure 3 shows a resulting reproduction in ¼-scale in (I presume) Tim’s hand. This rapid prototyping might be done using a milling machine to carve the shape into a block of material, or with other techniques which build the shape up with layers of cut paper or by selective hardening of liquid plastic cast in thin layers. Many other methods can be imagined as well, the point being that once the original scan has been done and the digital recording is made, it can be used in many different ways and preserved digitally for future developments.
Fig. 3 - Shield figure petroglyph reproduced
with rapid prototyping. Photo: Tim Urbaniak.
Think of it, a virtually perfect, permanent, three dimensional record, made with no touching of the rock face, digitally preserved for future possibilities. Thank you Tim!

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