Drawing has been one of the preferred rock art recording techniques for many years. It has the advantage of being inexpensive and requiring little extra equipment. It also allows the recorder to use his/her interpretation to fill in details that are very faint in the original. This, of course, presents both positive and negative problems and consequences. That is, the subjectivity of interpretive conventions can become a serious disadvantage. Faintness and superposition are common problems in rock art that are perhaps best overcome by drawing and tracing techniques. Sketching or drafting is likely to be inaccurate if methods are not tightly regulated. Drawing also has the disadvantage of requiring substantially more time and skill by the recorder than does photography. Drawing is faster than tracing but less accurate. Sketches or drawings have another advantage over tracings in that they avoid rock contact.
To be of use, drawings must be rendered to scale and incorporate a consistent set of visual conventions such as the use of solid lines, dashed lines, stippling and cross-hatching. Since drawing is most useful for marginal glyphs, it is important to check sketches and rock surfaces under various lighting conditions. Field kits should contain regular drawing paper, graph paper, erasers, pencil sharpeners, colored pencils, pencils of assorted hardness , and mechanical pencils. Field drawings should be inked at a later time and then checked against the original. A drawing can be one of 3 types, each successively more time consuming: a field sketch, a ruled drawing and a grid drawing. A sketch is rendered unaided. A ruled drawing uses a flexible ruler to measure key features and is done on graph paper. A grid drawing makes use of a string grid over the original to produce accurate scale and composition.
We would expect drawings to be used rarely for recording petroglyphs except in special circumstances such as when the glyphs are very faint, or partially obliterated. In many of these cases, computer aided drawing can be more reliable. Drawings should be rendered as a matter of course for 'panel complex' and 'unit' maps.
The following convention sets are compiled from various rock art recording manuals [2:Texas]
Glyph Drawings:
Panel Drawings:
Panel Complex:
Site Drawings:
Tracing requires more time than drawing, but produces a more accurate result with less skill. Mylar, drafting film, prepared acetate, or paper may be taped over the glyph or panel. Care should be exercised to never place tape over any rock art. Another tracing method involves the use of rice paper soaked in water and rolled onto a rock with a sponge roller. Tracings can also be made on transparent plastic film such as polythene, initially rendered in dark felt-tipped pen, then copied with India ink. The result of a tracing is durable and geometrically stable; such images can later be digitized and stored on a computer. Like drawing, tracing is time consuming and requires a certain degree of skill.
We would expect tracing to be used only when other methods are unsatisfactory for specific and limited areas.
3. Computer Aided Drawing
In addition to normal drawing, with modern digital equipment in the field, it is possible to use guided drawing. This concept begins with a digital photograph that is then printed lightly on paper. This printout can be accomplished in the field with a digital camera. The recorder can then return to the petroglyph and compare the image to the original glyph, making sketches of added areas or deleted areas in addition to other notations. Both the original image and the corrected drawing can be retained in the database for comparison and analysis.
This kind of drawing is a new technique and we cannot predict how useful it will be until we have field tested it. But it is likely this method will be very useful and used frequently. To annotate photographs with drawings will become a powerful recording technique.
4. Rubbing, Moulding & Casting
These methods require physical contact with the rock surface and may produce some damage to petroglyphs. Rubbings, moldings, and castings are also extremely time consuming. A traditional method of recording petroglyphs has been to make rubbings, using means similar to those for copying tombstones, other finished stone, as well as brass and copper engravings. Rubbings are not geometrically accurate. Further, rubbings with muslin and cobbler's wax have been shown to affect cation-ratio dating.
It is not clear whether casts can safely be made of engravings on hard surfaces using elastomer silicones and polyesters. These cause no apparent damage to the rock substrate, and are quick and easy to apply, producing precise and resistant results [Bahn&Vertut]. However, we do not know if these methods interfere or affect rock art dating techniques. Although mouldings and castings can be an extremely accurate way to reproduce petroglyphs, they present difficult storage problems.