The following note to T.H. Lewis' publisher in Chicago describes the
rubbing methods Lewis used to record the shape of petroglyphs during his
Northwestern Archaeological Survey from 1883 to 1894. A few minor
typographical and spelling errors have been corrected. The discussion of
reducing the pictures to a smaller scale was apparently for the benefit
of the publisher. Please note that the rubbing procedure described is no
longer recommended by rock art experts due to wear and tear damage that
can result to the petroglyphs. A "no touch" policy is now generally
recommended and today no greased paper should ever be applied to a petroglyph.
Even running your fingers over a petroglyph may disable potential absolute
dating techniques due to the oils in human hands.
"The pictographs described in this book, whether on boulders
or rock ledges, have been copied the natural size, by first marking around
the margins of the grooves with a very soft lead pencil, and then laying
the greased side of a sheet or tissue paper over them. If the surface of
the boulder or ledge was smooth or nearly so, simply rubbing the outer side
of the paper lightly with the hand, was sufficient to get a good negative
impression, Removing the tissue paper and placing it on a sheet of thick
white paper, I then traced the positive lines.
On rough surfaces I first marked around the margins of the grooves, as described
above, and then laying the paper over them, traced the outlines as seen
through the paper, while it was in place on the rock.The space between the
lines (on the paper) represents the actual width and shape of the groove.
The short notches or irregularities in the outlines are caused by the irregularity
of the surface in most cases, and it is impossible to copy them in such
a way that the roughness of the surface of the rock will not be shown in
the line,
In reducing the pictures to a smaller scale, the smaller notches in the
outlines should be straightened, and the blurred portion should be ignored,
running the line at those points with the general trend of the well defined
line.
The original tracings were not made with a view of reducing them by photography,
and they are entirely unfit for that purpose. In order to be thus reduced,
there should be new tracings made from the original tracings, following
the above rule for making reductions, and making the lines on the new tracings
uniform in width. T.H.Lewis"
