Concerns regarding the Conservation
of Functional Horological Objects
Jim Moss
Professional Horological Conservator
Private Practice
Littleton, MA, USA
Professional Associate Member, AIC
©
2003 James Moss
This document is a response to a query
in the Conservation DistList, Instance: 16:46,
Friday, January 31, 2003, subject "Tall case clock". This is a start
in the discussion about conservation of horological
objects but is not definitive.
If the clock is to function, the
following items need to be considered:
Using a 10,000 year view point as a measuring stick, consider the following:
Rarity
If the clock is one example of a
design of some very low production number, even if the maker is not well known,
then it needs to be conserved with care. The low production volume imposes a
severe limit on the amount of historical information that we have available on
this particular maker and that limit dictates, in the case of a requirement of
functionality, a replication of the artifact.
A replication will relieve the
problems associated with the replacement and replication of worn components as
well as the disappearance of historical information. It will not, however,
relieve the costs associated with functionality: regular maintenance, damage by
handling, and wear. It will also be expensive to make the replication.
In the case of non-functionality: the
development of a careful Conservation plan for the protection of this object is
absolutely required. Permit me to digress for a moment and express this
thought: so often we have a tendency not to protect the un-popular makers of
the day as well as we protect the popular but in the grand scheme of things,
they are all equally important.
If the clock is "one" of
many (in other words, a production clock... easily found with many other
"clones" in existence), then as long as one or two are held in
"trust" somewhere on this earth, the operation of this object along
with the ramifications of function is certainly acceptable. The difficulty here
is determining "if" any "perfect examples" are held in
"trust" and if that "trust" is irrevocable! Replication and
replacement of worn components of a "production" object deemed
acceptable for use as a functional object is a reasonable and acceptable
position to hold in this case. But, remember that the supply of production
clocks or watches is dwindling with no replacements in sight!
Loss
of Historical Information
Historical information can be lost
in many ways such as: handling, cleaning methods, exposure to UV, wear, and
treatment techniques. But, what is the historical information that we are
losing?
Some historical information can help
us to identify and understand the materials that were used as well as to
contribute to the larger picture of where these materials fit into a countries
socio-economic development. Likewise, determination of how these materials were
manufactured and used can also point to information about a countries economic
and technological growth. Thus it is important to determine if the metal was
hammered or rolled or cast or filed or machined or produced using cost reduced
methods (such as is being done today). Replacement of components within an
object may not totally compromise the historical worth of the object in the
larger sense but will render interpretation more difficult in the future. If
the object is a "one" of a kind, then the impact from repairs is
significant: if the object is "one" of many, then the impact is
lessened. Cleaning can affect ability to track an object from its generation to
its present location: various "dirt" or "salt" deposits can
provide precious clues to an objects past but to some
observers can be visually unbearable. Cleaning can erase clues about the
environment in which the clock or watch has existed. And, without documentation
prior to any treatment, we've lost it all!
Wear
In all cases of functionality (this
can be applied to all manner of functional objects such as airplanes or trains
or machine tools, etc), wear is going to take place: wear of the bearings (or
bushings if the bearings have already been replaced), wear of the pivots that
rotate in the bearings and wear of the sliding components such as the
escapement pallets along with their respective escape wheel teeth, wear of the
conjugate surfaces of the striking and chiming levers, and wear of surfaces of
the gear teeth that are in contact with one another. In fact, all wear is
caused by sliding one surface over another be it sliding or rotating.
Consider, for a moment, the motion
of a shaft in the "Time" portion of the clock or watch: each time the
clock "ticks" the shaft will perform the following actions:
"stop", "roll ahead", "stop", "backup"
( if the escapement is a "recoil" escapement), "stop", and
then repeat the sequence over and over. When the shaft "rolls ahead"
it tends to climb up on a wave of lubrication: when it comes to a
"stop", it sinks down through that wave to rest very close to the
bearing wall. The "dwell" time or "stop" time is dependent
upon the escapement design but it can be sufficient to allow the shaft to
settle down so close to the bearing wall that it is possible to catch a high spot
of material and the next time it "rolls ahead", it will displace that
high spot of material from the bearing wall: this is a form of wear.
Consider, for a moment, the motion
of a shaft in the "quarter chiming" gear train: those shafts rest in
one position for almost 10 minutes... plenty of time for the pivot to approach
the bearing wall: far more time that then "time" train has. This
resting period can cause more wear in this train than in the "time"
train if allowed to cycle an equivalent amount as the "Time" train.
Consider, for another moment, the
motion of the shaft in the "hour striking" train... it rests in one
position for almost 50 minutes: far more "resting" time than either
of the other gear trains and far more potential to produce wear as a result of
penetrating the barrier layer of lubrication prior to motion.
Airborne
Abrasives
Now, consider, for a moment, the
introduction of airborne abrasive particulate and what would happen if a
particle interjected itself between the pivot/bearing interface.
Because the bearing material is usually softer than the pivot material and the
abrasive particle larger than the irregularities of either surface, the
abrasive particle will become imbedded into the bearing wall and act as a piece
of "sandpaper" or as a "lap" and cause wear to occur on a
regular basis. If the lubrication is renewed without the pivots being polished
or the bearings being replaced, the wear will occur faster because the abrasive
particle's cutting edges will be kept clean by the lubrication. (This is
sometimes evidenced when a clock has been run for a very long time without
maintenance and then is just "cleaned": it usually will not run
reliably after the "cleaning". This is because the bed of gunk that
has covered the abrasive particle was removed during the cleaning process. Now,
not only is the particle removing materials rapidly from the pivot but the
pivot and bearing are worn and don't fit together as well as they did before
the wear occurred.)
Wear can take place from a variety of
reasons in addition to the above noted ones. Wear can occur as the result of
gears engaging with one another and applying a pressure to the rotating pivots
causing the bearings to wear in one direction. Wear can occur as a result of
lubrication that has failed. Wear can occur as a result of a corrosive
atmosphere. And so it goes.
Lubrication
Part of the key to reduced wear is
the type of lubricant that is used: not all clock or watch lubricants are
created equal! What is needed is a long chain polar lubricant: one that can lay
molecular chains of lubrication between the interface of the pivot and the
bearing wall and have one end of that chain "attached" to either the
bearing wall or the pivot. The same holds true for any other sliding components.
But, this lubrication is not a total solution and it never will be. Lubrication
will not prevent wear: it will only slow it down. At the atomic or crystalline
level, it is impossible to completely separate the sliding surfaces. Clock and
watch lubrication is not pressurized so the components are not always floating
on a surface of lubrication and in the long run, pressurized lubrication will
not prevent wear either.
A common mistake is oiling the clock
or watch without proper cleaning or the addition of new lubrication to the old.
Not only is there a very good chance of an unwanted chemical reaction between
the two lubricants but the lubricating qualities of the new lubrication will be
negated or degraded by the presence of the old lubrication's compromised components.
Another result of adding lubrication is that the clock is allowed to function
far beyond a reasonable maintenance period and this will cause severe wear to
occur.
The older lubrications were made
from sperm whales or porpoises and contain various acids as well as organic
components: one will lead to corrosion of the metals and the other to
decomposition of the lubricant.
Environment
(Including Visitors)
As you can imagine, the welfare of
the object is subject to its environment also! Having a stable temperature and
relative humidity can play a large role in preventing surface corrosion and the
development of micro-climates within the mechanism. The volume of visitors and
the frequency of the fluctuation of temperature and RH as well as the number of
particulate generating objects in the vicinity such as rugs and open windows
will drastically affect the MTBT (mean time between treatments) and a short
MTBT can be an expensive proposition.
A
MAJOR PROBLEM: Who is qualified to conserve a clock mechanism?
Not all clock repair people are
created equal: not all have the same training nor background
nor the interest in preservation. There are very few trained horological conservators in the world but there are
hundreds of local repair people. Most of these people either learned this trade
by using text books with techniques that can be very damaging to an object or
they apprenticed under someone who used those texts. Very few of the local
clock repair people have a detailed understanding of the mechanics of horological objects let alone the understanding to use
techniques that would be harmless to the object. There are some schools that
produce very well trained and informed students in the mechanical aspects of horological mechanisms such as the British Horological Institute (BHI) but they do NOT teach
conservation techniques or philosophy and they still use the same text books
with the same techniques that can be damaging to an historical object. Other
schools have attempted to teach the conservation of horological
objects but have not been very successful at this point.
The best candidate of all as a horological conservator would be a person "program
trained" in conservation and who has attended the BHI. or
the WOSTEP program (Watchmakers of Switzerland Training and Educational
Program). There are no serious 2 or 4 year horological
schools in the United States as of this date (there are some evening classes
and a couple of schools for hobbyists).
Conservation is an attitude: they
may have the best training in the world but not have a conservation view point
or attitude or values and those are the most important ingredients.
So, how do you judge if the local
repair person is capable of "conserving" your clock? Of necessity,
you need to know something about the appropriate conservation techniques used
to conserve a clock, you need to know the person's source of education, you
need to know something about the mechanism, and the mechanical techniques used
for the "repair" of them: you cannot rely on the recommendations of
others in your field. Regardless, closely monitoring of the treatments while
they are happening is absolutely necessary when hiring outside contractors:
their motivation is money and yours is preservation and usually the twain never
meet.
In addition, it has been my
experience that detailed past treatment documentation is at best scanty or
non-existent. You must demand and receive documentation on all of the chemicals
used for cleaning, the names of the coatings used if any, the manufacturer of the
lubrication as well as its description and the chemical analysis, a
"before" and "after" report of the bearings replaced, the
pivots polished, and the components replicated as well as any adjustments that
were made. There must be no secrets!
To help you understand a small
amount about the conservation of functional clocks, I am providing you with
some conservation view points as well as some information about some repair
techniques. The following information is not a full
fledged treatise on the subject but it will be enough to help you. Also, be
sure to use the references that I have provided to you at the end. Just a note:
the conservation of non-functional clocks is different; it is less invasive.
Bearing
Techniques
Bearings are holes in the front and
rear plates of a clock movement into which the ends of the shafts (called
pivots) are placed. The purpose of a bearing is to locate accurately the
position of the shaft. Accurate location of a pair of shafts insures that the
proper placement of their respective gears and insures efficient transmission
of the available power. As the bearings wear, the distance between the gears
increase and causes the transmission of power to become more inefficient and at
the same time increases the wear of the gear teeth, pivots, and bearing walls.
When bearings need to be replaced,
no more material should be removed than is necessary to retain the new bushing
safely and to provide proper centering. It is usually necessary to file out the
worn bearing hole until the hole is once again centered about the original
center location. If at all possible, removal of material should not exceed the
diameter of the original oil sink. The use of pre-manufactured bushings
(readily available from suppliers) that are not of the proper length must be
avoided because the length of the journals will be too short to support the
loads imposed upon them. On the other hand, the use of pre-manufactured
bushings that are too long is also inappropriate because ,
in time and through wear, they will effectively eliminate the end-shake
necessary to allow the shaft to rotate freely. Stacking pre-manufactured
bushings to make up for the lack of journal length must be avoided as the join
between the two bushings will provide a place for abrasives to gather. It is
best to make bushings to fit that to try to make do with what is on hand. When
making bushings, one must make sure that the alloy is known and that
information is contained in the documentation for the clock or watch.
When a bushing has been installed,
the oil sink should match the shape and depth of the original but should not be
blended to the point of being unable to be identified as a replacement. If at
all possible, the bearing material should be of a slightly different mixture of
the same alloy type so that in the future ready identification can be done with
an SEM or visually.
Oil
Sinks
Oil sinks are concave hemispherical
cavities that surround the end of the bearing and are located on the outside of
either the front or rear plates. Their purpose is to hold and prevent the
spread of the clock lubrication that is applied to the bearing. Most people
apply far too much lubrication to a clock or watch pivot and this usually
causes the lubrication to run out of the bearing and by capillary action will
cause the bearing to go dry. The proper amount of lubrication is when a
micro-meniscus forms between the pivot shaft and the base of the oil sink.
Cleaning
Techniques
Unlike a painting or a sculpture
that can have its surface "easily" cleaned, a clock movement has to
be completely disassembled, then cleaned of surface accretions, and then
re-assembled (usually it is not as simple as this although we all wish it were
so!). Clock movements can consist of up to 500 individual components and each
component has a series of surfaces that need to be cleaned. Effective and safe
cleaning cannot be done by the "dip and swish" method! And,
cleaning should not be done using an ultrasonic cleaner: it must be done by
hand.
The preferred cleaning solution used
by most clock repairers is an aqueous ammoniated cleaner either
pre-manufactured or home-made. In any case, exposing stressed brass ( most clock components contain stresses) to ammoniated
cleaning solutions will produce a known and verifiable effect: Stress Corrosion
Cracking (SCC). SCC may not happen instantaneously but it will happen and it is
not reversible. Some repairers use a pre-manufactured
"non-ammoniated" cleaner but instead of ammonia, it contains one of
the following relatives of ammonia: "mono" or "di" or "tri" ethanolamine. These particular
chemicals are also capable (an
have been documented as causing) of producing SCC. This means that you
have to insure that your object is cleaned in a manner that is harmless to your
object. (Ref: Ammoniated cleaning solutions by James Moss: American Horological Times, Volume 22, Number 2, February 1998;
British Horological Journal, Volume 139, Number 8 .)
For cleaning a clock movement, I
presently use hydrocarbons and alcohols in combination with manual labor, fine
brass and steel brushes (only occasionally), stiff bristle non-metallic brushes
(all of the time) and sharpened pieces of wood called peg wood: I do not use an
ultrasonic. If steel brushes need to be used, they should only be used on steel
components: likewise brass brushes should only be used on brass components
because if a brass brush is used on a steel surface, corrosion cells can be set
up and over the long term and in the right conditions, corrosion can take place.
Restricted use of the metallic brushes is necessary as they will remove any
protective oxide layers even with careful use.
Pivot
Polishing
The purpose of the pivot is to work
in conjunction with the bearing to locate accurately the position of its related
shaft. Each shaft has two pivots: one on either end. As stated in a prior
paragraph, accurate location of a pair of shafts insures that the proper
placement of their respective gears and insures efficient transmission of the
available power. The pivots must be polished to a mirror finish (they will
appear to be black if properly polished) and usually, but not always, they are
cylindrical and have parallel sides. A polish less than mirror like will
produce wear as it is actually a miniature rotary file!
Replication
If a component is damaged or worn to
the point that simple polishing will not allow it to work properly, then the
entire component needs to be replicated. This means that if there is a gear
that is too damaged to work properly, then the gear and its shaft and any other
of the assembly's associated components need to be replicated and the original
assembly needs to be stored safely. You should be able to substitute either
assembly into the mechanism without any additional work, and the clock should
work properly (assuming that the part needing replication was complete and
whole). Replication of only part of an assembly many times can cause more
damage to the overall assembly during the process than is necessary.
Replications should be made of material similar in composition as the original
but sufficiently different that analysis can easily determine the difference
between the original and the replication. All replications must be signed and
dated and labeled as a replication.
Maintenance
Period
Because the preservation of a
functional object is paramount, cleanliness is one of the major keys to
longevity. This means that frequent cleaning of the clock movement is
imperative. From a long term preservation standpoint, the MTBT of once every
year would not be unusual and would be recommended: a MTBT once every two years
would be approaching the "too infrequent" mark.
Coatings
Under normal circumstances, clock
and watch components in functional objects should not be coated as there is a
possibility that the lubricants used could react adversely with the coatings.
Brass has a naturally occurring oxide that will cover the brass surfaces with a
perfect "non-holiday" coating and is the best that nature has to
offer. Coatings applied by spray gun or human beings are fallible and need to
be replaced approximately once every 20-25 years under the best of conditions.
By utilizing the oxide coating the brass, the process of removal, preparation,
and re-application of an organic coating is one more intervention that will not
be needed and one less chance for damage to the object.
Techniques
to Correct for Wear
Many times, in an effort to retain
historical information, a person will move the position of a component to an
unworn section of its conjugate component. After a few moves such as this,
there will be a permanent loss of information about the method of manufacture
of that component: in the interest of the preservation of historical
information, it would be better that the entire assembly be replicated and the
original assembly be saved with the one spot of wear than to "fix"
that one spot by repositioning components.
Handling
Winding the clock, setting its hands
and the various dials, as well as moving the clock can expose the object to
serious damage. Always consult with a responsible horological
conservator for proper instructions concerning these actions before performing
them. There are many variations and there are no absolute rules regarding the
above processes.
Non-Functional
Clocks and Watches
Even if you choose not to run the
clock, this decision does not abdicate the necessity for preventative
conservation and stabilization. Surface accretions, coagulated lubrication and
lubrication that contains an acidic component, as well
as other contaminants need to be removed from the interior and exterior
surfaces of the mechanism. Protection from corrosion needs to be provided.
Coatings need to be carefully determined before application.
References:
"Ammoniated cleaning
solutions" by James Moss: American Horological
Times, Volume 22, Number 2, February 1998; British Horological
Journal, Volume 139, Number 8 .
Conservation of Clocks and Watches edited by Peter B. Wills, BHI, ISBN 0 9509621 4 7, 1995