Longcase clocks, are known as Grandfather clocks, and tall case clocks in the USA. If properly cared for, longcase clocks will give hundreds of years faithful service. Their value can only increase if they are looked after, and by seeking the services of a competent horologist, it is possible to maintain a clock in near original condition for a very long time indeed.

Firstly, remove the pendulum and weights. This is crucial because otherwise the delicate suspension spring at the top of the pendulum rod will bend, or break. Remove the hood and gently lift the pendulum rod from inside the trunk. Check that the brass piece at the top of the thin suspension spring lifts completely clear of the bracket in which it sits, and let the pendulum down gently, making sure the large brass block at the bottom of the suspension spring passes through the slotted part through which it goes, called the crutch. The pendulum should descend freely. If it seems to stick, don't pull, just gently move the pendulum from side to side a little, making sure that the pendulum rod is not twisting, and it should come out.

The weights unhook from their pulleys. Winding the clock before removing the weights limits the degree of unravelling of the lines around the barrels.

If it is necessary to touch the movement (the works), wash and dry your hands thoroughly, because any fingerprints you leave behind will contain natural oils which will cause corrosion over time. For this reason horologists wear white cotton gloves when handling clock parts.

Cleaning should be confined to the dusting of the exterior of the clock case. In particular you should avoid dusting a dial. If a cleaning cloth catches the tip of one of the hands, it will bend the hands when pulled away. Once a hand has been bent it is seriously weakened and may break when it is bent back into place. Moreover, depending on the type of dial, a wiping action may smudge any ink (due to dampness in a cloth) or remove lacquer.

Use the tip of a finger to move the clock's minute hand. It is unsafe to turn the hands backwards past the hour. Avoid touching the surface of the dial. Acid from your hands will tarnish the brass. This may not be strictly true for a lacquered dial, but even if the dial is lacquered, the lacquer will eventually wear off. For clocks with rack striking, if it is necessary to turn the clock past 12 o'clock, pause at just after 12 and let it strike. Ideally this precaution is not necessary, because there is a mechanism in the clock to allow this to happen safely, but in my experience it is rarely set up correctly. If in doubt, wait until the striking has finished.

Clocks with count wheel striking should be advanced one hour at a time, to allow the striking to keep up with the indicated time. If the time indicated is between about 5 to the hour and the hour, the strike will have warned, and turning the hands back will allow the strike to run. This can be used to advantage where the clock has count wheel striking, which can get out of step with the time indicated. The striking can be advanced by turning the hands to 2 minutes to the hour and then turning them back to about quarter to the hour. This will trigger the next strike. With repeated steps the striking will eventually fall back into sync. Clocks with rack striking can never get out of sync.

The process of setting the time on a clock is formally known as hand-setting.

Thirty-hour clocks do not have winding squares and are not wound with a key. When winding a thirty-hour clock it is necessary to pull down on the rope (or chain). The rope goes around the pulleys in an endless loop. Pull one of the sides that goes through the counterweight. Take some of the weight with the other hand as the rope/chain is pulled, to relieve the winding mechanism of some of the strain.

Inherent in a thirty hour rope/chain winding mechanism is maintaining power. This keeps the wheels turning during the winding process.

For eight-day clocks use a cranked winding key and wind more slowly as the weights approach the seat-board. Stop winding just before the weights touch the underside of the seat-board. If the clock will not go for eight days, the lines may be too short. Even worse, the clock may not be in its original case, which would have been taller and provided a longer drop for the weights. Note whether the 2 weights are level at the end of the week - if not then this may indicate there is a problem with the striking. The left hand weight is for the striking. If it is lower than the going weight on the right then this indicates that the strike train is not locking correctly and striking too many blows; if it is higher than the going weight then this indicates that the striking is not delivering the correct number of blows. It is worth placing a cushion (or other such shock absorber) in the bottom of the case. One day a line may break and the weight will drop to the bottom of the case. A shock absorber will minimise damage to the case, and soften the sound of the thud.

Few eight-day longcase clocks have maintaining power, and during winding there is no drive to the wheels to keep the hands turning.

One can apply one's own maintaining power during winding very simply. Apply a little pressure in a clockwise direction to the minute hand, but not so much as to make the hand move. This will be quite enough to make the second hand advance with each swing of the pendulum. Whilst applying this pressure, wind the going side, which is always on the right hand side. Take care not to touch the dial with your finger or hands at any time.

If the winding holes in the dial are obscured by brass shutters, then the clock has maintaining power. Maintaining power keeps the clock going during winding. There will be a cord or lever, which must be pulled before winding can take place.

Clocks with a deadbeat escapement will have automatic maintaining power, in a form known as Harrison's maintaining power. This is an essential feature of such clocks because the escape wheel teeth are so delicate that it cannot be left to chance that the winder will apply the maintaining power.

The going weight should weigh about 12 lbs and the striking weight around 14 lbs. The going weight is always on the right and the striking always on the left. If the going and striking weights are the same size, it would be wise to weigh them. A going weight of 14 lbs would eventually do a lot of damage to the clock. Furthermore, the amplitude of the swing of the pendulum may increase to the point where the pendulum hits the side of the case. The size of weight for a regulator is usually less than half that for a Longcase clock

All longcase clocks should be fixed securely to a wall to avoid the possibility that the case might move due to the swinging of the pendulum. Such movement will reduce the amplitude of the pendulum's swing and may loosen the joints of the case over long periods of time. A clock whose case is free to move may also exhibit a phenomenon known asThursday disease. Any movement of the case, however slight, will be transmitted to the weights. When the weights have descended to the point where the length of the lines supporting the them is the same as the length of the pendulum, the weights will swing in sympathy with the pendulum (but back to front rather than side-to-side). They will then hit the pendulum and stop the clock. This is known as Thursday disease, because the clock would traditionally have been wound on a Sunday and it would take until Thursday for this phenomenon to reveal itself.

Ensure the clock is vertical in both planes by using a spirit level. This ensures that the pendulum is clear of the backboard and allows the weights to descend without making contact with the case.

Some calendars advance twice a day, half a day at a time; others change once a day. The time at which they change varies from maker to maker. Once-a-day calendars may well start to change at 1am and complete the change two or three hours later. Twice a day calendars may change at about 3 am and then again at 3 pm. This means that the correct date is shown for most of the daylight hours. Whilst the change is still in progress it will show half way between the correct date and the date of the next day.

At the end of a month with fewer than thirty-one days, it will be necessary to advance the calendar manually to the correct date. Depending on the mechanism, there may be a risk of touching the dial with your fingers. The same care should taken as when changing the time to avoid tarnishing the dial by touching it.

Typically an average longcase clock should keep time to an accuracy of about 10 seconds a day which is roughly equivalent to a minute a week. The rate is likely to decrease in summer and increase in winter, due to the expansion and contraction of the pendulum rod with temperature.

The clock can be made to run faster or slower by adjusting the rating nut found under the pendulum bob. However, achieving the right setting can be a frustrating process for those who have not had much practice. Whilst a trained horologist can calculate the exact adjustment required, most clock owners perform this task by trial and error, and in so doing they often achieve equally good results. By keeping a record of how fast/slow the clock is running and of what adjustment is made, one can gain a feel for what effect a particular change to the rating nut will have. Note that as you home in on the desired rate, the clock will appear to become more sensitive to small changes.

If it gains, turn the nut looking from the front, to the left, which will lower the pendulum to make it go more slowly. If it loses time, turn the nut looking from the front to the right, which will raise the pendulum to make it go more quickly. Note that the pendulum bob must be free enough to descend of its own accord when the rating nut is lowered.

In times gone by, it used to be necessary to service a clock every three years or so, because the air was so dirty from coal smoke and smog in the atmosphere which would cause the oil to thicken more quickly and cause the clock to stop. With cleaner air and synthetic oils, a clock may well now be capable of running for decades without servicing. However, you would be well advised to have your clock serviced every ten years whether your clock stops functioning or not in the intervening period; if you leave your clock until it stops functioning altogether then the work required will be much more extensive. The popular view that a clock which has stopped "only needs a clean" may have been true in days gone by (when the intervening period between services was much shorter by necessity), but this will not be the case for a clock which has not been serviced for thirty years!

It is important that the restoration of the clock is done in a way that has minimal impact on the clock, having due regard to maintaining the clock in as near original condition as possible.

A gloriously polished and brilliant restoration may make the owner feel proud of his clock and want to show off how well it has scrubbed up. But beware; it certainly didn't leave its maker polished to a mirror finish. Such a clock is in anything but original condition!

Concentric graining on the chapter ring (which makes it look like a gramophone record) may be thought to be attractive, but it will detract from its value and it will remove the surface metal causing the engraving to disappear. Graining is a 20th century fashion, which has no place on an antique clock. Contrary to intuition, the ideal comment from a clock owner following the restoration of a clock should be, "Well it's been to the clockmaker but apart from the fact that it now goes, you can't tell by looking at it". The only exception to this is if work has been done to the dial.

The policy of the National Trust, is not to have any cleaning or polishing work done. Their attitude is that it removes the history of the clock. That is not to say the clock shouldn't work. The British Museum's attitude is that whatever condition an artefact came in, it should stay that way. Any artefact suffering from deterioration or corrosion will be conserved and stabilised to prevent further deterioration.

Not many of us have clocks that are worthy of a place in the British Museum, but the principle still applies. If repair work is restricted to making it go, then any restoration work can be undertaken after doing some research. Once restoration is done, it can't be undone, so think carefully before commissioning any work on your clock.

In particular, you should ask your horologist about his attitude to conservation. Repairs should be undertaken in such a way that the minimum quantity of original metal is removed and, any materials used should be of the correct type. For example bushes should be fitted without the need to file down the surplus on the inside of the plate, which inevitably removes metal from the plate. Where the presence of a bush can be detected, the old bush can easily be removed without any damage to the clock plate, and a new one inserted. Re-conversion to an earlier form of escapement, particularly verge escapements, must never involve drilling of new holes.

• The Longcase Reference Book John Robey, Mayfield Books
   
• Britten's Old Clocks and Watches, 9th Edition, Bloomsbury Books
   
• The Longcase Clock, Tom Robinson, Antique Collectors Club
   
• The Science Of Clocks and Watches, AL Rawlings EP Publishing
   
• Early English Clocks, Dawson, Drover Parkes, Antique Collectors Club
   
• English 30 Hour Clocks, Darken and Hooper, Penita Books
   
• Painted Dial Clocks, Brian Loomes, Antique Collectors Club