An investigation into movement finish - Up Close with the GO Panograph

[tempocalypse]

Here's something you might not be aware of: the blued screws also receive black polishing before the heat treatment.

Having done this, the process of black polishing is not all that difficult, just painstaking. Basically, you build a jig to hold the part in question at a set angle (the one you need to polish). You then take a sheet of good quality float glass, relatively thick, and then glue three sheets of mylar-backed diamond paper on that: one sheet of P1500, one sheet of P2500 and one sheet of P6000. The P1500 is grit 800 with an average size of 12.6 µm, the 2500 has an average size of 8.4µm and the P6000 4µm. Using just a small amount of watch oil and attaching the part in the jig (aka tripod), you start off the with P1500 to do the rough finishing, then to P2500 to remove any scratches and then finish with the P6000. The idea of using three is that if you have a problem due to a scratch at the P6000 level, you go back one step to the P2500 level, instead of having to remove a whole layer using the P1500 abrasive sheet.

The problem is that you do need to build a customized worktool to hold the item in a vice and be at exactly the right position. The screw bottom gets polished first, then you use a P1500 diamond bar to do bevel the screw slot and then a thin P6000 file to do the bottom of the slot and the beveled surfaces; then you do the top via the three steps as above. Hence you need a jig for the screw bottom, then a vice to hold the screw for the diamond bar and file (you can use a nice brass plate with screw holdings that you can also use for bluing for this purpose, works well place in a vice), then a final jig for the top plate. The tripod feet of the tripod jig for the top finishing of the screw get polished as well, so you have to adjust the fit whenever you put in a new screw to be worked on. Once you've got the tools, it's a fairly quick process: I think after a day I was putting black polish on screws at the rate of about 30 per hour. It does require significant concentration, good lighting and steady hands.

If you blue the screws without doing the black polish, you'll not get a very good finish (duh). Chemical bluing - the kind you see on a lot of Chinese watches, for instance - is easier, then the screws have only to be clean.

That said, black polishing and then bluing are attention to detail that raises the watch movement involved from the mundane to the sublime. :-)

Actually just reading through your comment once more... I am not entirely certain we are talking about the same process. Apologies if I misunderstood, misread or if its an issue of terminology.

But my understanding was that true Black Polish/Poli Noir/Tin Flat Polish requires the additional step of polishing using diamond paste on a tin plate after the various grades of paper have been used:

http://www.watchesbysjx.com/2015/01/...polishing.html

Given different and conflicting use of terminology I have not been so successful in nailing down a precise definition from various online sources of black polish but the impression I have so far is that it does involve a tin plate to qualify.

Something to add from GO's website which I've added to the original post

"In order to achieve an especially flat and lustrous surface, parts such as the swan-neck spring, regulator, or screw heads, which are particularly easy to view through the sapphire glass case back, are enhanced using the traditional but at the same time very labour-intensive process of tin flat-polishing.

In this process, diamantine (a polishing paste) is applied to a flat tin file, which the operator uses to file the surface of the part until it is completely even and gleaming. The process can take several hours and is checked continuously with the aid of a loupe.

Polishing of a swan-neck spring (including the perimeters and angled edges) takes around 1 hour; to polish a sound spring such as that found in the “Pocket Watch No. 1” can take from 4 to 7 hours. Tin flat-polishing has a technical as well a visual purpose. The surface of the material is enhanced and offers greater protection against damage by moisture in the air and oxidation."

The work on the swan neck and other complex shapes I imagine presents a significant challenge compared with screw heads

[tribe125]

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[tempocalypse]

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