А weekend job
Last week I cased one homeless pocket watch movement made in 1880’s by a famous danish watchmaker Henri-Robert Ekegren from Copenhagen. H.R.Ekegren worked for top horological companies Jules Jurgensen, Winnerl Paris, Golay Geneva etc. In 1891 Ekegren manufacture was taken over by Edouard Koehn, Patek Philippe director. So, it became a part of glorious Patek manufacture.
Original enamel dial, original hands, new custom made stainless steel case – all frontage in perfect condition. Highest grade lever chronometer movement features palladium hairspring, solid gold balance screw weights, ultra fine pallet lever and “swan neck” precision regulator.
The only confusion was about the caseback view. The movement kept uncased for a long time, stored many years in old watchmaker’s drawer. Little oil and moisture drops corrupted into visible dark tarnish spots.
Yes it was previously treated with cleaning powder. Yes it passed all standard procedures in watch cleaning machine with special cleaning solutions. It’s oiled, adjusted and runs perfectly! But these tiny tarnish spots causes just a resentment.
What a pity – perfect working movement with untidy back view. Actually it’s not a dirt, not a dust. It will not affect to a movement precision.
These spots are micro corrosion in a top layer of metal. So it can’t be removed with cleaning, special mechanical treatment needed.
Condemned to full refinish
To make visage improvement, I had to repeat a big part of movement work. First disassemble it again and put all clean parts to a new plastic tray.
Must exempt the mainplate from all bridges, wheels, screws, springs. We need an access to absolutely naked surface.
Remember how it looks before. Next I’ll try some methods to improve this view.
First approach. Hand rubbing
First simple method is to rub-off spots with cleaning powder and water. We rub it hard with fingers and cotton swabs. Sometimes it does help, but now you can see many traces of corrosion left after treatment.
Looks a bit better than initially, but not enough for a high-class restoration we ventured to do.
Not everything made by human hands is the best, especially in metalworks. But I had to try this smoother way first, sometimes it’s enough (not this time).
Invoke the Machinery
To make honest quality restorations, any watchmaker must operate with lathe and some other simple machinery. Next step we will brush the mainplate surface.
Use of sandpaper is unacceptable. Workpiece treated with sandpaper will look not vintage, but cheaply grinded. Also sandpaper can’t find a way to recessed balance slot, will leave it dirty.
We will process the mainplate with coarse diamond paste and grinding brush disk. Actually I tried dry brushing, but not succeded well, so decided to add consistent diamond paste.
Fix the mainplate in lathe using 3-jaw chuck. Put brush grinding wheel in hand engraver drill. Turn on both lathe and drill, touch workpiece with grinder and slowly feed rotating grinder from center towards the edge.
Arrows shows two simultaneous rotations (spindle and grinder) and motion from the center (orange arrow).
Сounter rotation of workpiece and grinding tool forms charming “sunbeam” pattern, it is well seen on diamond paste layer. Metal brush itself will not leave lines, but diamond particles makes it all very finely.
Next we rinse it extensively with unblended gasoline and wash again in cleaning machine. Well done this time!
The mainplate now looks near-perfect for it’s 120-years age. Smooth sunbeam lines are indistinguishable with naked eye, but makes spectacular play with light.
Now must treat every part
In contrast with such a shiny mainplate other parts looks insufficient shining. I had to spend some time to rub every bridge on generic rubber eraser.
Finally it’s time to assemble it all back! Wash all bridges in machine, oil and make final adjustments.
Now I’m satisfied with it’s view. Serene smooth shining does not attract too much attention, looks clean and vintage enough for it’s age.
Yeah this watch looks stunning, hope you would like it too =)
Described method is not suitable for gold-plated mainplates. Yellow gold-plated or white silver-plated mainplates can’t be easily repaired with brushing. We can make the same “sunbeam” pattern with grinding wheel, but after mechanical processing parts will need new galvanical plating.
It took about 3 hours for all operations. Actually I spent more time to compose this review in English =)