Why are they rubies in watches and not emeralds or topazes?

Question

I know that every mechanical watch has a ruby inside it, as a hallmark of quality and to help it work. Why not diamonds, or other gems then? why just rubies, mostly?

Answer 1

The jewels used in watches are usually rubies, sapphires (which are chemically the same as rubies), garnets and diamonds. After around 1900, most of the rubies used were synthetic. Before 1900, the jewels were either from stones that were too small or had too many flaws to be used in jewelry. In either case, they really weren't that costly. There is often a correlation between the price of the watch and number of jewels, but the jewels themselves are not the cause of this higher price.

Reducing friction is an extremely important goal in watchmaking. Jewels have two important properties that help reduce friction. First, they can be made to be very smooth, and therefore they let the metal parts slide easily. Secondly, they are very hard and therefore don't wear down very quickly. The gears in a watch are carefully designed so that the teeth roll on each other, rather than sliding. If the axle of a gear wears away the hole that it sit in, the gear will shift. That means the teeth will no longer roll on each other and therefore friction will be increased.

There are several different types of jewels used in a watch, the most common are:

Hole Jewels: These are donut shaped jewels that fit over the gear axles (in watch lingo, the wheel arbors).
Cap Jewels: These are flat jewels that are placed on the ends of the axles (arbors).
Pallet Jewels: These are brick shaped jewels on the pallet fork that alternately engage and release the escape wheel. The escape wheel is the gear with funny "boot" shaped teeth.
Roller Jewel: This jewel is on the large balance wheel that swings back and forth. It engages with the pallet fork on the end opposite of the pallet jewels.
The jewels are carefully shaped so that the capillary action of the oil causes the oil to be drawn toward the gear arbors instead of spreading out where it doesn't do any good.

Answer 2

WarLabRat is correct. They use rubies, diamonds, and sapphires for lack of friction when parts are moving and because they are strong so that take longer to grind down. You can buy extremely expensive (seen them over million dollars on tv, and they have had them on how its made) were you can see some gems due to a clear windows on the part that has the numbers.