3 jo PAINTING MATERIALS
Shell. From earliest times shells of clams and mussels have evidently been
favorite containers for paint mixtures. Prentice Duell says that shells were the
forerunners of the palettes of the Egyptian painters. They are frequently men-
tioned in the technical literature on painting for the Middle Ages and the Renais-
sance, and are seen as appurtenances in the painting rooms that are represented in
pictures as late as the XVII century. Small mussel shells are used still for the
so-called 'shell gold/ powder gold in an aqueous medium, as it is prepared in
France.
Sight Measure. Developed from the simple finder or window, which is an
opening cut into a piece of cardboard, the sight measure is made to establish
certain relations and measurements in the rectangles formed by such an opening
(figure ai). The purpose of the finder is to select out of the field of vision those
isolated areas which are to be the subject for representation. The sight measure
has the same purpose. It is a thin metal window, usually painted dead black, and
with a sliding adjustment fixed automatically at 10 units of width and running to
about 30 in length. As the slide is moved away from the end, a window is opened,
the measure of which, with respect to the width of the slide, is indicated by a scale
marked at the edge of the opening. The sight measure has probably not been
much used as a standard piece of equipment, but appeared in the catalogues of
artists' colormen towards the end of the XIX century.
Silver Point (see also Metal Point). This has undoubtedly been the most com-
mon of the metal points used for drawing. In all of these the principle is the same.
The support, usually parchment or paper, is coated with a thin ground of material
that has an abrasive character: calcined bone, chalk, fine pumice, or, more recently,
zinc white. Usually these grounds are held by an aqueous medium like glue size
and are very lean in their structure. When the silver point is drawn over a ground
like this, fine particles of the metal are taken off and left in the line that has been
described. It is a pale gray mark which in time corrodes slightly to a darker value
and a warmer tone. Probably the use of such a point developed from the stylus
which was a common instrument for writing or scratching on tablets of various
materials in ancient times. Certainly the silver point and various other points
were well established in use in the Middle Ages and, although the graphite pencil
has largely displaced them in recent centuries, the silver point particularly is still
favored by a few draughtsmen. In The Practice of Tempera Painting (pp. 44-45),
Thompson suggests silver point for modern drawing on papers tinted with zinc
white and other colors, and he speaks of an easily made point of silver wire set into
a propelling pencil holder.
Sketching Easel (see also Easel). Designed primarily as a light, folding, and
easily portable unit for holding a canvas or panel in out-of-door painting (figure
n, £), this type of easel has a number of different styles. All those advertised by
artists* colormen, however, are made with three legs, adjustable in height and
hinged from a small block where they come together at the top. Some have cross