What are these Seitz B-Jewels?

[VWatchie]

I bought this box of jewels a few years ago and noticed that the glass containers are divided into two sections. In the first section, the containers have a label with red text colour and always start with the letter B. In the second section, the text on the label is black and lacks the letter B.

There seem to be roughly the same number of containers in both sections, and each section has the same sizes of jewels. The only difference is that the jewels in the B section with red text have a slightly rounded, convex underside. My question is what are these rounded jewels for and if I can use them instead of the jewels with a flat bottom if a certain size is missing?

[praezis]

3 hours ago, VWatchie said:

My question is what are these rounded jewels for and if I can use them instead of the jewels with a flat bottom if a certain size is missing?

They are for balance wheels only and wheels with similar pivots (B = bombé).

You can use flat jewels for balance wheels (not recommended)  but no bombé jewels for ordinary wheels.

[nickelsilver]

You can use bombé jewels with regular pivots if you put the convex surface facing the shoulder. You see it on (primarily older) high end pieces, particularly nearer to and including the escapement.

Edited April 18 by nickelsilver

[RichardHarris123]

I looked up bombè, domed in French.  It's pronunciation is bomb, does a bomb (explosive device) get It's name from bombè? I know we're going off subject but it's interesting. 

[nickelsilver]

It's pronounced "bombay" like the city.  French for bomb is, , bombe, pronounced the same as in English. Bombé, bombe.

[Jon]

I picked up a similar amount of these jewels some years ago in a watch and clock fair. Every now and then they come in handy. This week I've got a rubbed in bombe jewel in the balance cock that is cracked and needs replacing. Very handy to have a vintage assortment of these type of jewels!

[VWatchie]

17 hours ago, praezis said:

They are for balance wheels only and wheels with similar pivots (B = bombé).

You can use flat jewels for balance wheels (not recommended)  but no bombé jewels for ordinary wheels.

16 hours ago, nickelsilver said:

You can use bombé jewels with regular pivots if you put the convex surface facing the shoulder. You see it on (primarily older) high end pieces, particularly nearer to and including the escapement.

Thanks for your answers! There seems to be a contradiction between these two answers, so perhaps I need to clarify. The flat and convex jewels look identical on the side facing away from the pivot shoulder. That is, there is an oil reservoir. I don't know if that changes anything but I thought it was safest to clarify since I didn't include a picture of the jewels from the opposite side.

[Neverenoughwatches]

1 hour ago, VWatchie said:

Thanks for your answers! There seems to be a contradiction between these two answers, so perhaps I need to clarify. The flat and convex jewels look identical on the side facing away from the pivot shoulder. That is, there is an oil reservoir. I don't know if that changes anything but I thought it was safest to clarify since I didn't include a picture of the jewels from the opposite side.

If frank says these bombè jewels are for balances and similar pivots then they are used cupped side facing the pivot and then capped i assume. In Nicklesilver's reply i guess that cup can also be reversed and used as an oil reservoir leaving the shoulder riding on a less frictioned domed surface.

1 minute ago, Neverenoughwatches said:

If frank says these bombè jewels are for balances and similar pivots then they are used cupped side facing the pivot and then capped i assume. In Nicklesilver's reply i guess that cup can also be reversed and used as an oil reservoir leaving the shoulder riding on a less frictioned domed surface.

Hence the use of them on wheels closer to the escapement that have less torque requiring efforts to reduce friction and are also uncapped.

[VWatchie]

1 hour ago, Neverenoughwatches said:

Hence the use of them on wheels closer to the escapement that have less torque requiring efforts to reduce friction and are also uncapped.

Yes, makes a lot of sense! Thanks!

[Neverenoughwatches]

19 minutes ago, VWatchie said:

Yes, makes a lot of sense! Thanks!

Kind of guessing here watchie with a bit of logic.

[VWatchie]

1 minute ago, Neverenoughwatches said:

Kind of guessing here watchie with a bit of logic.

That's what I thought, but as I said, it makes sense. See if any of our pros will have something to add.

[Neverenoughwatches]

13 minutes ago, VWatchie said:

That's what I thought, but as I said, it makes sense. See if any of our pros will have something to add.

When Nicklesilver mentioned the use of them on non coned pivots on older high end watches closer to the escapement.  That suggested to me  probably fourth wheels and possibly third wheels. The square shoulder rotatating on the much smaller surface area of a dome as opposed to a flat jewel surface. I'm curious as to why they are not used predominantly?

Edited April 19 by Neverenoughwatches

[nickelsilver]

I've seen some really nice early 20th century pieces where all the jewels, including center wheel, were convex. Definitely to reduce friction. It can be quite hard to tell if a jewel has olive holes, especially on small sizes, but that again reduces friction- as well as accommodates small misalignments better. Why they aren't used more often? I imagine it was found that at a certain point in the train the actual advantage became negligible, and the added cost on high production movements is why it's not seen on those, just higher-end pieces.

 

I did an experiment on a little 5x7"' AS 1012 a few years back. These things run OK sometimes, but often are absolute dogs. And AS made gajillions of them. I had a NOS novelty watch in for a service, ran OK flat, massive drop in amplitude vertical. Made like 3 staffs for it trying different pivot sizes, no change. Tried high quality (not Seitz) convex/olive jewels, no change- the original were flat, but could have been olive hole. Same for the pallet fork, then escape wheel, no change. Probably had 20 hours in the watch, new staff and new hole jewels through the escape wheel, no difference in running. Just a dog of a movement. But if I were making a watch I would use them, just because.

[VWatchie]

26 minutes ago, nickelsilver said:

It can be quite hard to tell if a jewel has olive holes, especially on small sizes, but that again reduces friction- as well as accommodates small misalignments better.

That's very interesting information. I haven't tried to see if my bombé jewel holes have olive holes but I think I should be able to tell on the larger jewels at least. See if I get a chance to have a look later today.

32 minutes ago, nickelsilver said:

Just a dog of a movement.

This little story was very comforting to read for a "bungler" like myself. That success isn't a given even for a pro. Thanks for sharing!

[Neverenoughwatches]

27 minutes ago, VWatchie said:

57 minutes ago, nickelsilver said:

Just a dog of a movement.

This little story was very comforting to read for a "bungler" like myself. That success isn't a given even for a pro. Thanks for sharing!

Plus the added foresight not to buy a watch with an AS 1012 inside it.