Most of us can conjure up an image of a lighthouse
beacon sending forth its light in the midst of howling wind, weather,
and pounding surf. It does not take much imagination for us to see how
these bluntly unforgiving environmental forces can threaten our nation's
lighthouses. Although we have lost treasured lighthouses to these environmental
forces, it surprises many to learn that when it comes to the classical
fresnel lighthouse lens itself, it is not environmental factors which
cause the most damage to them.
Based on the examination of dozens of deteriorated and damaged lenses,
the human factorvisitor contact, ill advised maintenance practices, lens
removal, transport and storage, and vandalismdoes the most harm. The next
most prevalent cause of damage results from the natural aging of the litharge
glazing putty which holds the glass and brass together. The putty can
release hazardous lead particles as it deteriorates, introduce stress
into the system, and eventually will no longer adequately support the
glass in the brass. The combination of these two factors can spell disaster
for a threatened classical lens.
How Should Lenses Be Treated?
Conservation of a classical lighthouse
lens should always begin with a condition assessment which looks at the
overall physical and chemical stability of the lens. Each of the constituent
materials is examined to identify health, safety, and maintenance issues,
and basic stabilization needs. The assessment should result in a treatment
protocol which addresses those needs. Treatments which extend beyond stabilization
are most often presented as treatment options because decisions about
restorative treatments can only really be decided when considered in a
broader context. Interpretive goals, historic preservation goals, funding,
staffing, and operational issues all come to bear on restorative treatment
decisions. The question is not, "What kind of brass polish is best
for a classical lens?" but rather, "What aspect of the lens'
history is being preserved if it is re-polished?"
Context issues are not new to either conservation or the historic preservation
field. The Secretary of the Interior's Standards for the Treatment
of Historic Properties states that, "the historic character of
a property (or object) will be retained and preserved(and that) each property
will be recognized as a physical record of its time, place, and use. Changes
to a property (or object) that have acquired historic significance in
their own right will (also) be retained and preserved." The standards
suggest that an appropriate level of conservation treatmentbeyond stabilizationis
best made by considering the context.
Historic Preservation most often concentrates on the preservation
of historic evidence as preserved in wear patterns, operational damage,
and/or interactions with historic figures and events. Evidence that a
lens was properly maintained (polished, cleaned, etc.) would be pre-served
just as evidence to the contrary could also appropriately be preserved.
For instance, chips in the prisms would not necessarily need to be filled
to achieve historic preservation, especially if that damage is noted in
the keeper's log or associated with an important personage or event.
Historic preservation can be less expensive and may require less preventive
maintenance than restoration to period. This type of restoration
is most often sought in instances where a lens remains in its historic
architectural context. If that context is furnished and interpreted to
a specific historic period, then period restoration is appropriate for
the lens as well. A period restoration would address the most recent damage
or deterioration and leave that which might reasonably be attributed to
the interpreted period.
Period restorations can be less expensive and less difficult than full
restoratio n, which is likely to be carried out when the interpretive
goal is for the optic to appear as it would have when it was installed.
It is also often the case that an optic that has been removed from its
tower and is out of its historic context will be a candidate for full
restorationespecially if the lens is used as an interpretive tool to demonstrate
the optical principles of the classical fresnel lens. The thinking is
that damage (such as chips in the glass) presents a distraction to the
viewer when the interpretation concentrates upon optics and illumination.
If less complete restoration is desirable because of cost considerations,
then discrepancies between appearance and interpretation can be successfully
addressed with interpretive panels which discuss treatment and preservation
Full restorations are often undertaken in the belief that a full restoration
is historic preservation. Factors, including material selection and application,
combined with the skill and experience of personnel can produce a variety
of results. Misguided treatments can permanently scar the glass or brass
and otherwise permanently damage the lens. Given the extraordinary value
ascribed to classical lenses and the inherent risks in working with hazardous
materials, it is imperative that a treatment plan be proposed by experienced
offerors and that proposed treatment meet both the preservation objectives
of the client as well as the actual needs of the lens. In addition to
contextual considerations, there are, of course, the realities of available
funding and ongoing maintenance issues which will impact final treatment
If the original deteriorated litharge
glazing putty can be stabilized, then one of the major threats to classical
lenses can be brought under control. As straightforward as this solution
sounds, successful treatment depends upon a number of factors, including
the composition of the putty, its porosity, previous treatment history,
and the degree to which it has physically deteriorated. An alternative
to the stabilization of the old glazing putty is its replacement, a time
consuming and expensive option. Re-glazing is difficult because the lead
putty is a hazardous material which requires special handling and disposal.
The good news is that it appears that the French manufacturers changed
the formulation of their glazing putty sometime around the turn of the
century, opting for a lead oxide which appears orange-red in color instead
of the more traditional lead carbonate which appears white. The change
produced a more porous, slightly softer putty. A porous putty can be consolidated,
hence stabilizedan impervious material cannot. New low viscosity silicone
resins appear most promising as an encapsulant and consolidant and low
molecular weight resin systems are also being evaluated.
Repair and replacement of damaged
or missing glass is the most sought after restorative treatment. To date,
the least expensive option for the repair of broken or chipped prisms
makes use of either an optical grade epoxy or epoxy/acrylic resin adhesive
systems. More "reversible" adhesives are also finding applications
for use in repair. Replacement of damaged or missing lens elements is
another restoration solution. Options include replacement with cast epoxy,
cast acrylic, or replacement with glass. Each approach has its particular
advantages and disadvantages. The highest quality glass replacement is
also extremely expensive. On the other hand, lower cost cast epoxy replacements
can discolor with time.
The other treatment most often requested is that the brass support structure
be returned to some previous appearance by repolishing it. The problem
with polished copper alloys is that either constant maintenance or a brass
coating that protects it from further corrosion is required to retain
the polished appearance. Coatings are great when applied to small brass
museum objects. They can be applied without much trouble, and when the
time comes they can be removed and reapplied fairly easily. Not so with
a 10 foot high by 6 foot wide first order lens which is 85 percent glass
and 15 percent brass.
The decision to polish lens brass should be made only after a close examination
of its condition. A highly developed layer of cuprite (the reddish brown
corrosion layer often found on copper alloys) can indicate that the lens
did not receive periodic cyclic maintenance during the historic period.
Cuprite is a rather benign form of corrosion often thought of as a protective
form of corrosion. It is only bright brass which can quickly corrode.
Can the brass be returned to its former glory? Yes. Does the reddish brown
form of corrosion need to be removed? No. Brass treatment and the impact
re-polished brass has upon interpretation, historic preservation, and
future maintenance should be thoroughly discussed by all affected parties
before re-polishing is undertaken.
Conservation treatments are available now which
will preserve the beautiful classical fresnel lenses in our nation's lighthouses.
Architectural conservators, objects conservators, and historic preservation
specialists continue their search for even better materials to improve
techniques for treatment in the hope that a classical lens will no longer
need to be removed from its tower because it is unstable. If a lens must
be removed for other reasons, stabilization methods and improved packing
techniques help ensure a safe relocation. In large part, it is the public's
keen interest in these historic beacons which is helping to pre-serve
them. Public support of preservation oriented institutions like the Lighthouse
Preservation Society, the U.S. Lighthouse Society, and the new National
Lighthouse Museum (to name a few), helps ensure that the classical fresnel
lens will remain an integral part of lighthouse history.
Greg Byrne is a conservator at NPS Harpers Ferry Center of Conservation.