SECTION 7 LENS FIRST AID
A. Identification. Loose prisms must be stabilized to prevent catastrophic
damage. There are two parts to this procedure, one dealing with a barrel-type
(onmidirectional or drum lens) lens panel and the other dealing with the bull's-
eye panels. To stabilize loose prisms, have on hand a roll of Tyvek tape
(available from book restorers), a supply of tongue depressors or Popsicle
sticks, and exterior vinyl spackle (EVS).
B. Litharge. Litharge, or putty, is made of white or red lead, linseed oil and
calcium carbonate (lead-oxide replaced white lead after approximately 1900)
and is a health concern for people working around lenses. As this material
ages, it becomes brittle and if crushed may become airborne and can be
inhaled by all that come in the vicinity of the lens--especially those who
provide maintenance. When performing your lens inspection look carefully at
all of the glazed joints to determine the condition of the litharge. DO NOT
DIG AT THE LITHARGE! If it looks intact, leave it alone. If powdering, flaking,
crumbling, or otherwise deteriorating, encapsulate the litharge using the
following method. Apply Tyvek tape near the edge of the prism where the
repair is being made. This allows a much faster cleanup to the lens elements
after this procedure is completed. Using very thin strips of soft wood (tongue
depressor) or a flexible artist spatula (do not use metal implements), apply
Exterior Vinyl Spackle (EVS) to the surface of the litharge (an individual's
gloved little-finger may also be an acceptable tool for application of EVS).
Shape into a narrow fillet between the frame and prism. DO NOT ATTEMPT
THIS PROCEDURE ON BULL'S-EYES. EVS dries fairly quickly and is easy
to use. When the EVS is dry, take a small paintbrush or Q-tip and paint the
joint with an exterior flat white latex paint. This will help seal the porous
surface and protect it from absorbing too much moisture. We recommend
coating all the litharge to prevent it from becoming airborne and to tighten
minor cracks in the glazing. This process is meant for someone with a lot of
patience; however, the end result accomplishes a safer environment to work
in and is reversible for future work. Remember to wear the proper safety
equipment and dispose of all contaminants as prescribed by Federal and
State regulations.
C. Barrel Lenses. On a barrel-type lens (drum lens), the litharge and wedges
secure all prisms, protecting them from falling out of the frame. To stabilize
loose prisms, run a strip of Tyvek tape to conform to the shape of the prisms.
Do not remove any wedges. Leave them in place if possible, as they serve
two very important functions. The wedges keep the prism in focus and also
act as a shock absorber so the glass doesn't contact the metal frame. If
wedges are missing, try to locate them at the base of the lantern. If none are
found, cut a tongue depressor or Popsicle stick to an appropriate size to
support the prism in the frame. Old wedges are sometimes tapered so that
excess clearance can be taken up by sliding two opposing wedges together
to make them thicker. The wood may be cut so that it is thick enough to
7-1
Previous Page
