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Demagnetisation of a mechanical watch

How to demagnetise a mechanical watch yourself
Author: Edgar Colomb, Liestal, Switzerland
Online since: 02/10/2014, Number of visits: 162094

The problem

When I was handling your magnets, I inadvertently magnetised my mechanical watch. As a result, it was five minutes fast every day – simply unacceptable. It is most likely, that the balance wheel spring was magnetised by mistake.
But whenever super magnets cause a problem, they can also solve them. Here is my suggestion for a low-cost watch demagnetisation, which I successfully tested on my own expensive watch. I am a physicist, but the instructions were written in laymen’s terms.
non-magnetic material
non-magnetic material

What does "magnetised" mean?

The atomic molecular magnets in non-magnetic materials are omnidirectional. Their effect is cancelled out.
magnetised material
magnetised material
In magnetised iron/steel (most of) the molecular magnets are aligned in one direction and the effect is cumulative.
Iron/steel can be magnetised by using super magnets, for example.

Methods of demagnetisation

In general, there are 3 options for demagnetisation:
  • Apply heat above the "Curie temperature" (768 °C for iron). Molecular magnets will lose their orientation if the thermal motion is sufficiently strong. Quite obviously, this is not the correct method for expensive watches.
  • Extreme jolts and blows. Expensive watches don't like those either.
  • An external, in strength decreasing, alternating magnetic field will disable the orientation of the molecular magnets. This is the correct method, not just for watches!

Practical application

Glue a neodymium rod magnet (for example S-06-25-N) or several small disc magnets (Caution, don’t use magnets that are too strong!) to the head of a thick nail and insert the nail into the chuck of a drill or cordless screwdriver. Then, with the watch a few millimetres away, start operating the drill at low speed. Now very slowly move the drill away from the watch to a distance of about 10 cm. The result in my case: The watch is again keeping accurate time!
I had this idea because the local watchmaker wanted to charge an unrealistic price for a demagnetisation with special equipment and estimated that this procedure of a few seconds would take one week.
What works for watches can also be applied to other objects.
A note from the supermagnete team:
What worked for the watch of Mr Colomb may not necessarily work for all other inadvertently magnetised objects. For valuable items, we recommend that you consult an expert (i.e. a watchmaker). We, here at supermagnete, cannot offer any guarantee whatsoever that the method used by Mr Colomb is going to work for other objects – improper handling or the use of magnets that are too strong may make the problem even worse.