Friday, 22 January 2016

Restoring a Silver Watch Case

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A while ago I posted a description of how a watch movement is cleaned, in this post I explain how I restore a silver watch case. The case in question was made by John Woodman of Smith St, Northampton Square, London in 1888.

From the wear pattern you may be able to see that the back of the case is depressed, there is also a dink bottom left and there is a lot of pocket wear, in reality it actually looks worse than in the picture. So something had to be done.

The first stage is to get rid of the worst of the muck and oxidisation, this is done with silver polish and a glass fibre brush.

If this were not done the next stage would not work as effectively and the fluid would have to be changed more frequently, perhaps after each case.

The ultrasonic cleaning is primarily to get into the parts other processes cannot reach including into digs and scratches. The fluid bath is detergent based and the case will stay in for 30 minutes which seems about optimal for a silver case.

The second ultrasonic machine shown is loaded with a solvent based cleaner that I use for cleaning movements.

The next stage is to press, rub or hammer out the back and the dents. This process will be different depending on the way the case is made and any finish such as engine turning on the back. Swiss cases in particular are sometimes made with a bezel similar to that on the front with a silver disk inserted - if you press on that to hard it will come out and be a devil to get back in and it you hammered the edge probably impossible.

It is better to press or rub rather than hammer as it will cause less damage to the inside which is difficult to burnish out due to the shape of the case and the necessity of preserving the hallmarks. The amount of work done on the outside has therefore to be balanced with the amount of damage to the inside and possible distortion of the case which may or may not be readily correctable.

The picture above shows the case after this work, the dink still visible but it is now more of a scratch or dirty mark.

For a case with a smooth back now comes burnishing with increasingly finer abrasives. A balance has to be struck between the amount of silver removed compared to the gain achieved in appearance and possible loss of structural strength.

In general I do not try and take out all of the marks but to still give a nice finish. All of this is done by hand.

Now comes the polishing, again by hand, the picture here was taken just short of the end of the process which will be finished just before the movement is ready for final refitting so as to minimise any new marks.

A similar process to the above would be used for a solid gold watch but most of these steps can't be used on gold plated watches because they have a very stiff inner core which makes pressing out dents difficult, although not impossible, and more importantly any hammering or use of abrasives is likely to go through the gold plate exposing the inner core.

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