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Conservation of Clocks

By Julian Cosby

Clocks are familiar objects with a familiar function. Viewed dispassionately, they are special-purpose machines designed to run at a constant rate, and therefore pose a fundamental problem: you must decide which of the clocks in your care are to be static or working objects.

If a clock is to run, it will need regular maintenance in the form of winding, setting, regulation, cleaning and lubrication. But even the best maintained clocks wear out as they run; and careless winding or setting can damage mainsprings, hands, dials and other components. This means that some parts will inevitably degrade to the point where they no longer function. At some stage you must decide whether to replace the worn parts, compromising the object's integrity, or to stop the clock.

Perhaps the best compromise is to combine both static and working displays. Where resources permit, it may be possible to supplement the objects themselves with replicas or working exhibits.

Which clocks will remain stopped and which could be run is a decision that must be taken against the background of the museum's care and acquisition policies and normal conservation criteria. Ask a specialist conservator for advice on the choice of suitable objects and their care and operation.

Up-to-date documentation and conscientious logging are important accompaniments to any working clock in the collection (see the fact sheet on Larger and Working Objects). Logs for working clocks should describe more than just major overhauls and maintenance schedules or the object's loan history, and must include such seemingly minor events as weekly windings and settings.

Types of Clock

The grandfather is an example of a longcase clock. These normally consist of a movement resting on a seatboard and concealed under the hood. The body of the clock case is known as the trunk and rests on a suitable base. Both the going (time) and striking chains of these clocks are powered by descending weights.

Smaller clocks in the collection may include bracket (fusée) clocks, mantel, table and wall clocks, and French and English carriage clocks. There may also be novelty pieces, perhaps of relatively recent origin. (Chronometers, watches and electronic timepieces are outside the scope of this fact sheet.)

The largest clocks are those from church towers, stable roofs and similar locations. Centuries-old turret clocks sometimes survive in dark corners of church towers after newer versions replace them. Whether they are working or not, their large size makes them interesting objects for display.

Materials

Clocks use a variety of metals, commonly brass, iron and steel, in their mechanisms, but a potentially huge range of materials - including glass, stone, woods and plastics - in their mountings or cases. They may be combined with other objects, such as barometers. Time displays may use paints, luminous materials, enamels, silvering and other fragile materials. And some clocks - certain longcase and French carriage clocks, for example - are valued as much for their cases as for their movements.

These other materials will require their own care regimes. A longcase clock can be regarded as a mechanism housed in a separate piece of antique furniture, so conservation issues concerning the case should be referred to a furniture specialist. But any operations performed on the mechanism should not harm or stress the case, and vice versa. For example, the vapour from certain woodworm treatments can damage brass components.

Storage and Display

The normal museum virtues of a suitable, stable environment apply as much to clocks as to any other object. A good compromise environment to safeguard movements and cases alike is 15°C at an RH of 45-65%.

Don't be tempted by authentic locations. A mantelpiece over an open fire is not a healthy environment, even for a mantel clock, and windowsills offer harmful fluctuations of temperature and humidity.

Physical stability is very important too. Pendulum clocks in particular must not rock or wobble while they operate. Unstable mounting will affect timekeeping, and may tilt components into potentially damaging positions - for example, a driving weight may rub against the interior of a case at the bottom of its travel. Changing a clock's location and/orientation will alter the relative loading and stressing of the moving parts; think of a longcase clock that is moved to a perfectly level museum site after a century on the tilted floor of a farm kitchen.

Longcase clocks must be firmly attached to the wall. When attaching other types of wall-mounted clock, try not to rely on a single hook, which will allow the clock to swing. Use suitable quick-release fittings - firmly attached clocks may be safer from the security point of view, but if fire or other disaster strikes will you be able to get them out in a hurry?

Keep all cases locked. Label and identify the keys, and keep them in a central, secure place with the winding keys.

Cleaning, Maintenance and Lubrication

A regular, conscientiously applied care programme is essential. The key care factors for a working clock are:

  • cleanliness
  • lubrication
  • observation and inspection
  • winding, setting and regulation
  • documentation and logging

Cleanliness is vital for the long-term and safe operation of a clock. Dust and dirt, combine with oil to produce a grinding paste that accelerates wear on all moving parts. A clock taken from storage or after a period of inactivity should not be restarted or oiled without a thorough clean. Because dust penetrates into the bearings and bushes, you may need to ask a specialist to dismantle the clock for cleaning and oiling.

The dust factor also militates against stop-start operation - for example, if you decide to preserve a valuable clock by running it for short periods only. Dust penetrates during the stopped periods and the result may be worse than the effects of continuous running. Frequent and invasive cleaning after dismantling is not the answer. Where a clock is run continuously for part of the year, allow it to run down before stopping it, then cover it securely against dust and make sure it is inspected by a horological conservator for cleanliness and lubricant condition before restarting it. Consider using special permanent dust covers over the movements of longcase clocks; these are concealed inside the hood.

Cases can be dusted gently with a soft brush. Do not use any spray or silicone polishes, and protect the dial when cleaning the glass. Never attempt any other cleaning, especially of vulnerable surfaces such as painted dials.

Mechanical clocks will not run without oil. Unfortunately, too much is as harmful as too little, attracting dirt and spilling over on to other surfaces such as dials and cases. Even the best oil eventually congeals as fractions evaporate and degrade and dirt is drawn into the mix. Clocks should be lubricated with special clock oil, not general-purpose household oils that may contain clogging additives, and the work should be undertaken by a specialist.

As a rough guide, a working clock in good condition and free of dust will need oiling every three years or so, and a full strip-down and clean every eight or ten years. Turret clocks need more frequent lubrication, especially if they are operating in their original or similar dusty environments, and may need oiling every year.

Visual inspection of clock mechanisms and parts for wear is an important aspect of the care programme. Look for bright, reduced or distorted surfaces among the moving parts, and chipping, flaking and discoloration on dials, hands, etc. Try to get used to the normal sights and sounds of the clocks in the collection too. You may be able to detect a change, such as a clock ticking out of beat (unevenly), and thus gain an early sign of an adjustment or wear problem before it has a chance to cause serious damage.

Adopt a conservation approach towards any necessary repairs. Always repair a part before replacing a whole; ensure that all repairs are named, dated and identifiable as such, and label and store all removed parts in a container set aside for that particular clock rather than a general-purpose 'junk' box.

Keys and Winding

Most clocks are powered by energy stored in a coiled spring or from the potential energy of a raised weight. Except where a weight is raised directly by pulling on a chain or rope, some kind of device - a key - is needed to store the necessary energy. There are two types of keys in common use: the 'butterfly' key, and the crank or winder.

The familiar butterfly key is turned between the thumb and forefinger. Turn it slowly and steadily, half a turn at a time - larger angles will make it difficult to count the turns at each wind. Crank keys permit a continuous turning motion so are more suitable for raising weights than the butterfly. Whatever type of key is in use, count the number of turns at each wind. Before you begin turning, ensure that the key is fully home on the square, and that you know in which direction to turn it - most, but not all, clocks wind in a clockwise direction. Support weights when pulling or winding them up; this reduces chafing or stretching on the cords and chains.

Each clock should have its own key - don't share keys between clocks, even if they fit well - and this must fit the 'square' on the shaft exactly. An ill-fitting key or improvised tool will soon round off the shoulders of the square. Identify all winding and case keys using sticky labels (dangling tags may scrape against vulnerable surfaces during winding), and store them together in a secure place - away from the clock and public access, but quickly accessible in an emergency.

Some authorities recommend that a pendulum clock should be stopped before winding. To stop a pendulum clock, gently obstruct the pendulum's swing at one end of its stroke, where it is almost stationary, rather than in mid-swing. Then slowly return the pendulum to its mid-position. Note the position at the end of the stroke; gently move the pendulum to this position and release it to restart the clock.

If a clock is to be left stopped for any length of time, allow it to run down fully if it is spring wound. This stores the spring in an unstressed condition. A weight-powered clock can also be run down to remove the loading from the gear train, but this may allow the weight cords or chains to hang out of the winding barrel on their securing lines alone. For this reason, it may be wiser to stop weight-driven clocks in a partly wound condition.

It is extremely easy to damage the spring or weight system, and other parts of the winding mechanism, by careless winding. There is rarely any need to wind a clock right up to the stop. You should know - or must find out - how many turns the clock requires at each wind, which implies that a clock should be wound at a fixed interval (normally weekly). For example, an English carriage clock may need to be wound some 28 half turns with a butterfly key every seven days. Clearly, irregular winding will not preserve the correct number of winds - 28 half turns every six days, say, would soon produce overwinding.

Such winding details should be documented, and the number of turns must be logged at each winding. Set aside a fixed time each week for winding the clocks and correcting their time displays, and follow a planned, documented sequence without rushing.

Setting and Regulation

Not only do visitors prefer clocks to be working, they expect them to keep good time too. Accurate timekeeping is the intended function of the clock so this is not an unreasonable expectation, but it implies high standards of care and maintenance, and an organised approach to regulation and time setting. Besides, poor regulation will mean increased wear and disturbance from the incessant correction of the time.
Always wear cotton gloves when winding, setting or regulating clocks. The regulation of clocks with internal regulators - for example, carriage clocks and others using balance wheels - is best left to a conservator. Some French clocks can be adjusted by a small square over the twelve on the dial. Use the correct (normally watch-sized) key, and only make small adjustments at a time; clockwise adjustment normally makes these clocks run faster.

Pendulum clocks are regulated through changes in the pendulum length - a long pendulum has a longer period than a short one and thus beats more slowly. There is usually a screw or nut under the pendulum for adjustment. Screw it upwards (shorter pendulum) to speed the clock and downwards (longer pendulum) to slow it. Adjustments should be small: first, stop the clock, then turn the screw - on a longcase clock, one turn of the regulator may change the setting by 30 seconds a day. Restart the clock and observe the effect over several days.

Some longcase clocks may have had their driving weights increased to correct poor timekeeping, but this 'solution' simply masks the effects of long-term wear, and increases the stresses on the mechanism. If the weights are 12 or 14 lbs or heavier, stop the clock and consult a conservator; it may well need a major overhaul.

Where the time on a clock is set by moving the hands, always move the hands forwards unless you have expert knowledge that they can be moved backwards with safety. Move them near the centre, at the butt of the hands rather than at the end. This reduces the risk of damaging the hands or the mechanism and of scratching or soiling the dial behind the hands. If you encounter strong resistance when trying to move a hand, stop immediately and take advice.
Use a good watch recently synchronised with an electronic reference to set a clock. Stop the clock, where this is feasible (as with a pendulum clock, but not with a carriage clock, say), and advance the hands to a minute or so past the current time. Restart the clock when the watch time reaches the preset clock time.

Take care when adjusting other settings. Second hands are almost never adjustable, so do not try to move them. Features such as calendar and astronomical dials may be adjustable, but remember that their movements are synchronised with other operations of the clock. In particular, never try to set such features when the hour hand is at or near twelve. Certain kinds of striking mechanism may fall out of phase with the clock - for example, striking the wrong number of hours, or the hour on the half-hour. With care, these can set back in phase, but you must know the correct technique before you attempt this.

Ask a conservator about the care, setting and regulation of these features. Make sure that the recommended techniques and operations are recorded as part of each clock's documentation, and passed on to the staff responsible for winding and setting.

Sources of Information

British Horological Institute
Upton Hall, Upton
Newark
Nottinghamshire NG23 5TE
Tel: 01636 813795/6
Fax: 01636 812258
Email: clocks@bhi.co.uk
Website: http://www.bhi.co.uk

Further reading:

Old Clocks & Watches and their Makers,
Britten, Bloomsbury Books, 1986 - 9th Edition.

English Domestic Clocks, Cescinsky & Webster, Chancery House Publishing Ltd.

Early English Clocks, Darwin, P. G. Droner, C. B. and Parkes, D. W., Antique Collectors' Club.

The National Trust Manual of Housekeeping, Sandwith, Hermione and Staunton, Sheila, Penguin Books in association with The National Trust revised 1993, ISBN 0 14 012344 X.

For more information about private conservation work please contact:

Conservation Register
Tel: 020 7721 8246

Conservation Register (Scotland)
Tel: 0131 668 8668

Copies of this fact sheet can be provided in alternative formats. Please contact Viola Lewis, Information Officer at MLA for further information.

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