Spatial Analysis Tools for Archaeologists


Grid Method For Visualizing And Archiving Visible And Invisible Rock Art

Bryan C. Gordon, Canadian Museum of Civilization (bryan.gordon@civilization.ca)


Introduction


In our websites, rock art research begins with two separate approaches: (1) above-ground archiving and enhancement of the art itself for later attempts at interpretation, and (2) subsurface testing for finding artifactual links to the art; in our case, that of dating. Dating is crucial to interpretation and is the subject of a related website linked to this one. The challenge in rock art research is to date regional art, then compare and interpret, before expanding to other regions and time periods. To interpret regional art it is best to archive regional art panels and motifs systematically, so that it is readily understood and accessible to others. The first step is gridding the pictograph site and panel.


Field Capture Technique


(1)  Stand 2m survey rod (more if needed) with alternating 2cm red & white or black & white stripes vertically to one side of rock art panel (Y-axis). From top of rod, suspend horizontal survey rod(s) above rock panel to opposite side and anchor. This is the X-axis for plotting subpanel widths for locating motifs (each 67 cm high in 2x3 digital photo ratio). Widths vary with panel size; some cave-rockshelter ceilings do not need gridding. Here, camera is placed on the ground as near to perpendicular to the panel as possible.

(2)  For vertical walls with art panels measuring more than several meters, place bubble-level tripod about same distance from the panel as it is wide to reduce parallax. Take subpanel telephotos from left to right in 1m increments with 10% overlap. Continue to second row, etc. Upper left subpanel would be X1Y1; second panel in vertical and horizontal order would be X2Y2; etc. Coordinates are references for later locating, enhancing and testing visible and invisible motifs for relationships.

(3)  For uneven panels, parallax will be reduced using subpanels and good zoom lens. A Macro-Nikkor 18-200 or equivalent handles both pictograph enhancement and 5mm soil ‘peels’ below art. Motif closeups prove particularly useful for penetrating lichens and enhancement, something we are working on at this time.

If rock art enhancement and dating are attempted in the field, archiving the art must be done separately from dating, as the camera and tripod used for identifying buried pigment particles will be in the way. This is especially true because soil testing is normally done vertically under the panel’s main motif. Other than enhancing the main panel in one photo to verify that you have covered invisible motifs, enhancing is best left for later lab work. The same is true for pigment particle identification in magnified soil ‘peel’ photos or on the glue papers used to recover particles for later SEM or X-Ray spectroscopy. Both are used to confirm pigment particle presence and are time consuming.


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