I was installing a new crystal on a beautiful Hamilton pocket watch today. I’ll write more about the watch in the coming days. I didn’t get the crystal installed yet. I had encountered this before but it has been quite some time. Old glass crystals for pocket watches were marked with a sticker on them to indicate the size. The sizing system is archaic, I like millimeters but the problem isn’t the system, it’s the sticker. These crystals go back quite some time and the stickers have been on the glass for 50 years probably. Unfortunately the adhesive they used has an acidic component to them and sometimes after removing the sticker you will find that the glass underneath is actually etched because of it. That was the case today. Ultrasonic, steamer, alcohol, acetone, even spit (the miracle solvent) couldn’t remove the “shadow” of the sticker. I’ll have to get another one. I don’t know how this could be prevented other than removing the stickers now before they etch other crystals, but than how would you sort them? Anyway, be aware, sometimes these crystals with stickers aren’t all you bargain for.
Regarding the numbering system: The crystals are marked with several numbers. Sometimes one of the numbers represents millimeter diameter, other times that measurement is absent. There is often a number to indicate how high of a dome the crystal has. This is usually a number between 1 and 10 where 1 is the highest dome and 10 is flat. The most important number is the diameter as measured in 16ths of a ligne. A ligne is 1/12 of a french inch. A crystal size 12 would measure 27.07 millimeters and a crystal size 24 would measure 54.13 mm. The crystal I needed today was an 18 9/8ths or approximately 41.9 millimeters.
As I searched for information about crystals and this old sizing system, I discovered a great blog. You should visit Montres/Watches. If you search for crystals it will turn up a nice conversion table.
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10 Comments
That’s interesting. Do you know why the stickers on most crystals have two sizes?
Vince, there is usually one size for the diameter of the crystal and another representing the dome. In addition sometimes the size is indicated in millimeters. That’s as much as I know.
Try the different fine polishing compounds you have. I have had success in the past simply buffing them on the buffer as they are only glass and lightly etched. Be careful not to break the crystal and slice your hands. Leather gloves are good. It is another story if it is scatched. Much more material to remove.
Jacob,
Thanks for the idea. I’ll try that out on Monday. Have you had luck with any specific compound?
While I have never attempted it, my thoughts were similar. I would think that Grobet’s/Vigor’s red rouge would be able to handle minor surface imperfections, as they do advertise it as a glass polish in their catalogue.
Amazon.com also carries M23P Glass Paste, which sounds like it could do the trick.
If all else fails, I would try diamantine, crushed into a very fine paste using Moebius 9010 as a binder. Half-micron diamond paste would do as well.
Just my thoughts. I would definitely experiment on a sample piece first though.
I tackled this crystal today. Red rouge was a big bust it didn’t result in any change. Simichrome actually had some effect but diamantine gave the best results. Unfortunately after putting half an hour into it, it still wasn’t good enough to put on the watch, although it was improved. This would work for a lighter etching, but his one was apparently quite deep. You could actually feel the roughness of the glass with your finger. I’ll be looking for a new one.
That’s too bad. Did the diamantine leave any traces? Or did it leave a nice polish on the unetched glass? It almost sounds like you need to take the glass down using some wet/dry emery paper before attempting to polish it out. Certainly not a quick fix to the problem.
The Diamantine left a very nice polish on the glass but it just wasn’t aggressive enough to work down past the etching. It appeared mostly to smooth out the edges giving the appearance that the etching was much more faint, although very well polished. I have ordered another crystal, let’s hope this one doesn’t have the sticker shadow.
I sure hope that the new crystal works out for you. Refinishing old crystals is something that I am curious to explore more about. I know that quite a few of the watchmakers who graduated from the Canadian Horological Institute, in Toronto, at the turn of the century went on to become optometrists as well as watchmakers. My guess is that the pursuit of that field likely sprouted from the need for them to fabricate crystals for watchcases.
Jp,
Try to use a little baking soda on the residual sticky part on the glass, first though, put the glass in a ultrasonic tank for 10-15 mins. Then try some baking soda mixed with some soapy solution, and runnig warm or tepid water. Brush with a toothbrush on the glass- I am guaranteeing the success of this operation!
Cheers,
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