WRITE A REVIEW
Clear up your questions about
crystals with this brief primer.
by Norma Buchanan
1.What is a watch
A watch crystal is a
transparent cover that protects the watch face. Note that, coincidently, the word
"crystal" is also used to denote the tiny piece of quartz that serves as an
oscillator in a quartz watch. These two types of crystals have nothing to do with each
other. The latter is usually called a "quartz crystal" to prevent confusion.
| 2. What are watch crystals made of?
They can be made of any of three materials: 1-
plexiglass (a clear, lightweight type of plastic), 2- ordinary glass - like that used for
windows, and usually referred to in the watch business as "mineral glass" or 3-
synthetic sapphire (see question 4). Some crystals are made of both mineral and sapphire
glass. Seiko, for example, makes some watches with crystals made of mineral glass covered
with a layer of synthetic sapphire. Seiko calls this composite material
| 3. What are the advantages and disadvantages of each
Plexiglass, as you
would expect, is the least expensive. It is also the least likely to shatter and the most
likely to become scratched. Mineral glass, even though it has been hardened by a tempering
process, is more likely to break than plexiglass. But it is also more scratch-resistant
than that material. Synthetic sapphire is the most expensive glass crystal material and
the most scratch resistant. Because it is so hard, it is also brittle, and shatters more
easily than mineral glass or plexiglass.
What exactly is synthetic sapphire?
It is a very
hard, transparent material made of crystallizing aluminum oxide at very height
temperatures. Chemically, synthetic sapphire is the same as the natural sapphire used in
jewelry, but without the coloring agents that give the gemstone its various hues.
When it is heated, the synthetic sapphire
forms round masses that are sliced into pieces with diamond-coated saws. These disks are
then ground and polished into watch crystals. (One reason sapphire crystals are relatively
expensive is that the tools required to make them are costly.)
Sapphire (whether natural or synthetic) is
one of the hardest substances on earth. It measures 9 on the Mohs scale, which is a system
for rating the relative hardness of various materials. (Diamond measures 10, the highest
rating.) Watch crystals made of synthetic sapphire are often marketed as "scratch
resistant", meaning they are very difficult - but not impossible - to scratch.
Diamond can scratch them; so can man-made materials that incorporate silicon carbide,
with, with a Mohs rating of between 9 and 10, is, like diamond, harder than sapphire.
These materials are sometimes used to make simulated-stone surfaces for furniture or
walls. The watch wearer should note that accidentally scraping a sapphire crystal against
such a surface could cause a scratch.
| 5. Can you tell if a crystal is made of sapphire by looking
No. Mineral glass and
sapphire generally look the same. A surefire way to tell them apart (albeit an often
impractical one) is with a scratch test, says Johann Jorgo, technical director at Baume
& Mercier Inc. New York. A stainless steel knife or screwdriver will scratch a
mineral-glass crystal but not a sapphire one.
| 6. Are Scratch-resistant crystals new?
No. Synthetic sapphire was invented
in the 19th century and first used for watch crystals in the 1960s. Now really all
high-end watch brands use synthetic sapphire crystals in at least some of their models.
7. Are all scratch-resistant crystals made of synthetic sapphire?
No. Some mineral-glass crystals are
also marketed as "scratch resistant." These crystals have a hard coating that
makes them less likely to get scratched.
| 8. The terms "lunette", "bombé", "chevé", and
"boule" are sometimes used to describe watch crystals. What do they mean?
All are French words that
refer to the shape of the crystal. "Lunette" simply means round - like a full
moon (lune means "moon" in French). Bombé, chevé and boule all mean concave,
There are other words used
to describe watch-crystal shapes. A "raised" crystal is flat on top but raised
up, like a birthday cake. "Shaped crystals" are any that aren't circular -
rectangles, square and ovals being the most common. "Cocktail" shapes are the
more exotic and extreme examples of shaped crystals. They include elongated baguette and
octahedral (eight-sided) crystals.
| 9. What are "anti-reflective" or
This type of crystal has been coated on one or both sides with a substance - the
same one used on anti-reflective eyeglasses - that lessens reflections and glare and makes
it easier to read the watch face. Anti-reflective crystals can be made of either mineral
glass or synthetic sapphire. One interesting feature of these crystals is that, viewed
from the front, they are virtually invisible because they aren't reflecting any light. In
some instances, the coating gives the crystal a telltale bluish tint, as it does on
eyeglasses. This tint is easiest to see if the watch has a light-colored dial.
| 10. How much do watch crystals cost to replace?
Consumers can expect to pay anything from perhaps
$20 to $25 for a plexiglass crystal to more than $100 for a shaped synthetic sapphire one.
(At Baume & Mercier, for example, synthetic sapphire crystals range from $65 to $135.)
The average cost of a round mineral crystal is about $30 to $60. An anti-reflective
coating adds to the cost of any crystal. In general, the more expensive the watch, the
more the consumer will have to pay to replace its crystal