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Pierre gomme-laque

3K views 15 replies 6 participants last post by  mars-red 
#1 ·
Pierre gomme-laque: A block of shellac mixed with an abrasive such as emery. Also known as a shellac stone. Used to create a straight grained finish on steel surfaces such as springs, levers, cap jewels, etc. The process of using the shellac stone is very similar to making flat polish except that the stone is moved across the surface in a straight line. Historically all parts that will be flat polished are first made flat using a shellac stone. This quote is taken from an article on Dufour by Ron Decorte. How and where can we buy this stone ? Is it makable by oneself ?

 
#4 · (Edited)
powdered glass, alu oxide, sand basicly something that is harder then what you want to grind and those previosly mentioned you can grind to size yourself with a mortle and pestle. what is used nowdays is more a paste then a powder but i guess one could dilute that with alcohol and let the abrasive stuff sink to the bottom

or buy the powders from bergeon http://www.cousinsuk.com/catalog/7/1118/1344.aspx i recomend you check a jewelers suply store to bergeon branded stuff tends to be a bit prisey

 
#5 ·
Pierre gomme-laque: A block of shellac mixed with an abrasive such as emery. Also known as a shellac stone. Used to create a straight grained finish on steel surfaces such as springs, levers, cap jewels, etc. The process of using the shellac stone is very similar to making flat polish except that the stone is moved across the surface in a straight line. Historically all parts that will be flat polished are first made flat using a shellac stone. This quote is taken from an article on Dufour by Ron Decorte. How and where can we buy this stone ? Is it makable by oneself ?
You can accomplish the same thing using abrasive paper - I use wet/dry abrasive sheets. I do this by laying the sheet on a piece of glass, then use a straight edge and draw the piece you want the finish on across the paper in one direction only. You can vary the grit of the paper to get different types of finishes.

Commonly used for apply straight grain finishes to Rolex case backs, movement parts, etc. For the Rolex case back, clamp it in your movement holder and use the holder up against the straight edge so the back does not rotate as you draw it across the sheet.

Hope this helps.

Cheers, Al
 
#6 ·
another old trick is to take a piece of pithwood cut it to the desired shape and rub in some abrasive paste hey presto you got a sanding block

or for small parts slam them into the pithwood the grip the wood smear abrasive paste on a piece of flat aluminium or something else that will grip the abrasive partikels and use that as a sanding stone

the problem with glass and abrasive paper is that the paper is soft even if you glue it to the sheet of glass so you might get rounded edges remember we are working with reeealy small parts here
 
G
#9 ·
Thanks for the input, I was reading this article too The Assembling and Testing of a Tourbillon Watch | My Tourbillon and they mentioned about using "lavender and almond oils with a diamond paste." What are the reasons why lavender and almond oils are used with diamond paste which is already in semi liquid form ? And where does one get zinc block for polishing ?
I think there's something lost in translation there:
In this article, the "diamond paste" is diamantine, not at all a modern diamond paste or powder. It's the same as Bergeon's 6807 one, if you scroll a few posts up.

A couple of years ago, I tried to make one of those "Pierre gomme-laque", but sadly, didn't succeed at all. A large volume of shellac is not easy to work with, it will quickly melt, and quickly solidify, before you can mix it nicely with emery powder.

I had nice results with 3M polishing sheets (I tried it from rough 40µ grit to fine 5µ). Diamantine isn't really used anymore in the real watchmaking world, they use 3M sheets or diamond pastes in syringes. My guess is that even Dufour uses these.
 
#14 · (Edited)
Whilst i was completing my WOSTEP course in 09 i spent the whole time trying to source any shellac stones but they are rare i was informed by nearly everyone i came across, my teacher eventually showed me atechnique that gives the exact finish.

3M paper with an adhesive back placed onto a stick of glass, i believe the grit was 20 or 15 microns, using a cork to support the piece that was to be finished.

Lavendar oil and almond oil were the favourite among a few watchmakers to polish pivots which a watchmaker told me on two occasions one at Audemars Piguet and another at Patek.
 
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