Theatre Design & Technology - Spring 1976 - 29

TECHNICAL REPORTS
A METHOD FOR ETCHING GOBUS

UNIVERSITY OF MICHIGAN

KEITH W. CLARK
Considering the unique potentialities and versatility
of gobos in stage lighting, their widespread use in certain
designs is not surprising. These thin sheets of metal
(known variously as "cookies" or templates), placed in
the focal plane of ellipsoidal reflector spots, project controlled patterns of light and shadow. These patterns are
a tool of great dramatic impact in the hands of a sensitive lighting designer.
Assuming he is aware of their potential uses, the designer may be frustrated in his attempts to achieve a certain effect. There is a practical limit to the accuracy with
which patterns can be cut in pie tins with a mat knife.
Expanded metal and similar material often used for gobos
tends to be too regular and the effect somewhat unconvincing. Ready-made die-cut gobos are available, but are
not cheap, and the designer must content himself with the
manufacturer's choice of pattern.
Such a problem was encountered in the Michigan Summer Repertory production of Mrs. Warren's Profession.
Craig Wolf, the designer, had called for gobos of an irregular pattern (Figure 1.), to be used in downlights. A
mottled effect was desi~ed, suggestive of sunlight filtering
through trees. One method of manufacture suggested,

Fig.1

Two etched gobos. Left, A Lighting pattern
for Brecht's Edward II. Right, The gobo described and used for Mrs. Warren's Profession.

I

I

USITT

FRED M. WOLFF

drilling, was rejected because it would appear too regular,
and it was felt that cutting the metal with a mat knife
would prove difficult as the holes were to be rather small.
At this point, the writer decided to employ the technology of the "printed" circuit in a different application; etching the gobo.
The procedure is quite simple. Begin with a blank of
brass shim stock cut to the dimensions of the gobo slot
in your instrument. This stock is typically .005-.015"
thick. Clean the surface thoroughly with steel wool to
remove oil and oxides. Using black enamel, paint around
your design on the metal. You must paint all areas where
you wish metal to remain. (Figure 1). Paint the entire
surface around the pattern, and then the entire back side.
It is necessary to paint the back so that the etching fluid
will be able to work from the front'side only. If you wish,
you can cover the metal with gaffer's tape, or even masking tape, as an alternative to painting - tape is easier to
remove afterwards, - but I advise going over the joints
between strips of tape with enamel to prevent leaks.
After the painted blank has dried it is ready for etching. A solution of ferric chloride is available from elect-

THEATRE DESIGN AND TECHNOLOGY

SPRING,1976

29



Table of Contents for the Digital Edition of Theatre Design & Technology - Spring 1976

Contents
Theatre Design & Technology - Spring 1976 - 1
Theatre Design & Technology - Spring 1976 - 2
Theatre Design & Technology - Spring 1976 - 3
Theatre Design & Technology - Spring 1976 - Contents
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