Material Facts: Karats to Kevlar

Steel, gold, gold plate, titanium, aluminum – the array of materials used to make watches is big and getting bigger. It can be a little confusing.

First, a note on nomenclature. When a person refers to a “gold watch” or a “steel watch,” he is referring to the material used to make the watch case. A watch can have a leather strap, but if it has a gold case, it’s a gold watch.

It’s a gold watch, that is, if the case is solid gold, not merely gold-colored or covered with a layer of gold.

Most gold is yellow, of course, but it can also be white or pink (sometimes called rose or, less often, red), depending on the metals that are mixed with the gold to make the alloy.

A karat is a unit of measurement used to denote the concentration of pure gold in the metal. Most gold watches are 18-karat gold. That means they’re 75% pure gold. Some are 14-karat gold, or 58% pure gold. The highest karatage possible for gold is 24-karat, which means it has no other metals mixed with it. (It’s never used for watch cases because it’s much too soft.) Bylaw, gold watches are labeled on the backs of their cases with the gold’s karatage. If the watch bracelet is inseparable from the case, as in a bangle-bracelet watch, the karatage may be marked on the bracelet.

Gold watches can be had for as little as perhaps $300, but most cost much more. Eighteen-karat-gold watches are more expensive than 14k-gold ones, as you would expect. And, of course, if the watch has a gold bracelet as well as a gold case, the price will go up significantly.

Among precious metals, gold is by far the most popular for use in watches. Silver is used occasionally. Platinum is, too, generally for very expensive mechanical pieces.

Gold-plated watches are more common than gold ones. Their cases are made of base metal – usually brass or steel – covered with a layer of gold up to 20 microns thick (but more often 10 microns or less). A micron is equal to 1/1,000 of a millimeter. The process of applying the gold is called electroplating. The gold used for gold plating is often higher than 18-karat because it provides a richer yellow color.

A gold-tone watch has a thinner layer of gold than a gold-plated one. Prices for gold-plated and gold-tone watches range from less than $50 to more than $1,000.

In recent years, steel has become an enormously popular watch material. It’s a fashion trend: tastes have shifted to white metals in general, with white gold also showing a rise in sales. The steel used in watches is stainless steel, meaning that it contains chromium, which forms a protective coating on the metal’s surface and protects it from corrosion.

Prices for steel watches range from under $50 to thousands of dollars. It may surprise some people that a watch made of such an inexpensive material, costing just pennies a pound, can be so expensive. It’s because the material a watch is made of is a relatively small factor in determining a watch’s price. Much more important are the cost of labor that goes into the watch and the amount of money spent promoting it. (The exceptions are watches set with substantial numbers of diamonds or other gems. For these watches, called jewelry watches, the price tags are more closely related to the value of the materials used.)

Some watches have touches of solid gold used as a decorative element on the bezel and/or bracelet. These are called, simply, steel and gold watches. Steel watches with gold-plated or gold-tone accents are usually called two-tone watches.

Titanium, a white, very durable metal, has also become more popular among watch manufacturers lately, a result both of the white-metal trend and the rise in sales of sport watches, for which this metal is well suited. Titanium is stronger than steel and is resistant to corrosion from salt water. (It is nonetheless easily scratched, which is why some companies coat their titanium watches with a protective material.) Titanium is also lightweight, weighing about 40% less than steel.

A few watches are made of aluminum, another white, lightweight, corrosion-resistant metal.

Less well-known materials are also used for watches, such as a combination of tungsten carbide and titanium, which results in a very hard, scratch-resistant metal. High-tech ceramic, the material used on the heat shield of the space shuttle, is also occasionally used to make watches.

Some manufacturers give their steel or brass watches a protective and/or decorative coating using a technique called PVD (physical vapor deposition). A gold coating can be produced this way, as an alternative to electroplating; so can a hard, durable layer of titanium nitrite.

Carbon fiber, a lightweight, strong material – either black or charcoal gray in color – is actually a combination of carbon fiber and polymer. It’s sometimes used to make watch dials and cases.

Three types of materials are used to make watch crystals, the transparent coverings over watch dials. One is mineral glass, basically the same type of glass used for windowpanes. Another is acrylic, a clear, durable type of plastic. Acrylic crystals are very shatter-resistant but tend to scratch easily. The third is synthetic sapphire, a very hard material used to make scratch-resistant crystals. Synthetic sapphire is essentially identical to the sapphire used for jewelry except that it’s man-made and, when produced for watch crystals, colorless. Like natural sapphire, it rates a 9 out of a possible 10 on the Mohs hardness scale. Diamond, rated at 10, is the only naturally occurring substance that is harder. Synthetic sapphire is also used for display backs.

Watch straps or watchbands (usually called watch bracelets when they’re made of metal) can be made of several different materials. Like watch cases, watch bracelets can be made of gold, gold-plated steel, gold-plated brass, steel, titanium or aluminum.

Most watch straps are made of leather. Calfskin is the most common type of leather. Another kind is kidskin, also known as chevreau (pronounced “chev ROW”), which comes from goats. Pigskin and lambskin are also used for watch straps. A group of watch-strap leathers called “exotics,” generally more expensive than leathers like calfskin or pigskin, includes lizard, crocodile, alligator, ostrich and shark. Sometimes calfskin is embossed with a pattern to make it look like an exotic leather. In that case, the leather is called “ostrich-look,” “lizard-look,” etc. The words “embossed” and “grain” are also used to describe these imposters, as in “embossed crocodile” or “ostrichgrain.”

Many watch straps are made of synthetic materials. They include nylon, plastic, rubber and Kevlar, which is so tough it’s used to make bulletproof vests. These materials are especially popular for use on sports-watch straps because they can stand up to the elements.