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Beginners often ask about where to find this or that crystal, as it happens replacing is cheap and easy as long they are just flat round ones. But the crystal may not be found as generic, or can be expensive, or hard to find. So good old polishing is needed. Here again my technique key points:

  • Crystal mounted on case, that will make it so much easier and safe to handle. Caseback removed, check below why.
  • Jeweller's motor or other rotary tool with a fixed stand. You really want a screen like a carton box.
  • Plastic roundel from a credit card as big as its size allows.
  • 600 grit wet paper. No other grit is needed, as it will lose abrasiveness already after 20 seconds of use and become comparable to finer grades.
  • Try to got directly over the deepest scratches, but without insisting too long (as in 5 seconds max) so to not dig valleys. Find the right compromise regarding the work angle, going flatly is good, but isn't even reasonable to try to sand the entire surface even.
  • Look at the white streaks from inside the glass while working. You will see if you're getting right at the scratch or nick because if so the defect will show up in contrast
  • Be patient with the paper stage. After a while it becomes hard to see if all scratches are gone, but you must remove them all before going to the next step.
  • You should have made a mental note or drawing of where the defects are, rinse it up and observe at different angles. In difficult cases you may need to replace paper once or twice.
  • Crystal will look now very foggy, that is normal
  • Once happy refit caseback and crown, or rodico in the tube. The diamond paste is much more messy and you don't want that inside the case.
  • Mount an hard felt wheel like 7 or even 10 cm dia, 2cm thick, place 1 cm of diamond paste (No. 10 or 14 good, but others work too) on the section toward you while keeping the crystal horizontal.
  • Let the wheel grab the compound one bit a time, keep well pressed up and go over until all pase is used and you can present the entire surface to the wheel, rotate the watch and collect the past on the other side, place it on the crystal again on the other side. You can't do more than 30 - 40 seconds of work before adding fresh paste. Usually I do 4 or 5 passes like that.
  • When working with paste is almost impossible to see the result with cleaning up. Clean with dishwasher detergent, dry it and observe well. Very likely you will notice some small defects, up to you if you want to go back to paper, concentrating on the spot only.
  • Final polishing can be done switching to another wheel and finer paste, no less that 10 as these have no practical effect. Cerium oxide is another option but I didn't try it extensively so far.

Below what I did today in about 20 minutes. The central scratch was quite deep. No final polishing or cleaning yet.

 

 

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