Sapphire Crystals Versus Other Types of Crystals
Comparing Watch Crystals
Protecting and displaying the face of a wristwatch, is a thin clear cover and what's typically referred to as, the watch crystal. They come in many different shapes and sizes, as well as in varying thickness and quality. Watch brands today, use several approaches and generally, your watch crystal will be fashioned from one of three distinct materials; plexiglass, mineral glass and sapphire glass.
The least expensive type of watch crystal is commonly referred to, by several names, including plexiglass, hesalite or acrylic and is basically a type of plastic. Like many products made from plastic, its very easy to manufacture and manipulate to whatever shape desired, and can be produced, at a very low cost. Perhaps, it's most significant downside is, that it is the softest material of the three options and therefore, can easily accumulate scratches. This can impact visibility, and then will require the owner's efforts, to either repolish or replace.
Redeeming this particularly negative attribute, is the fact, that it's the easiest of the three to repolish and again, very cheap to replace. It's also potentially the safest option to go with for high impact hits and bumps, as it won't shatter or break easily. When a plexiglass does break, generally, it will crack, but stay in place, protecting the wristwatch's dial and movement from further damage (though the watch wouldn't remain waterproof).
At the sensation level, how the crystal looks and feels, some consumers will appreciate it, and others will not. A plexiglass crystal could be described as warmer, less vivid viewing, compared to the other crystals, but a better method to determine that it is indeed plexiglass is by tapping it gently with your nail, as it will produce a plastic-like tone. For the most part, one will encounter its use in vintage pieces, as well as in very cheaply produced watches, though it is also used for various 'tool' watches when unbreakable is preferred to all other qualities.
Ever slightly more expensive, mineral glass crystals are used generally in wristwatches, at the lower end of the market. Almost identical to the glass contained in your windows, additional chemical and heat treatments are used to strengthen and harden the crystal. The main advantages to using mineral glass crystals are; decent scratch resistance, fine clarity and of course, the relatively low price. For what's basically the look and feel of sapphire, the mineral glass comes at a fraction of the cost.
The compromise, however, is the durability. It's much more scratch resistant than plexiglass, though lags behind sapphire's hardness ranking measurably. It's also significantly harder to polish than the plexiglass, and often, not worth the effort. Furthermore, it won't withstand the impact of plexiglass and even sapphire crystal. Some brands will employ additional techniques, to further harden or strengthen mineral glass crystals, such as coating them in a layer of synthetic sapphire, as Seiko has, with various lines of sports watches. It has nevertheless become, one of the several cost-cutting features, to expect on a wristwatch that's geared towards those on a budget, as well as a cheaper crystal replacement option.
The most expensive of the watch crystals, sapphire has gained popularity in recent years, and its use within the industry has exploded. Unlike its natural counterpart, this sapphire is synthetically produced in a lab. Aside from a few notable exceptions, high end watches built in the last couple of decades, are almost exclusively equipped with sapphire crystal.
Arguably, the most important of the sapphires' properties, is the superior scratch resistance, and only two minerals exist that surpass its hardness ranking (9) on the Mohs scale; moissanite (9.25) and diamonds (10). What this means is, that no other material poses a threat, in terms of scratching the sapphire, except for, of course, other sapphires. Another advantage of sapphire crystal is the high clarity. Often the crystal will have added, a special AR (anti-reflective) coating on one or both sides, and at times, be so clear, as to make the crystal, seem to disappear. It's preferable for sapphires not to be coated on both sides, as coating the outer face, generates the danger of it being scratched and ruining visibility.
Preventing sapphire, from reaching total superiority over the alternatives, are two factors worth considering. First, there is the high price. The process to create synthetic sapphire, is both time-consuming and labour intensive. Any watch featuring sapphire will cost accordingly. Another weakness to consider is the possibility of sapphire crystal to shatter. The hardy nature of sapphire renders the crystal somewhat brittle. In thick or domed sapphire crystal derived from reputable sources, it's less likely to happen, but still possible.
All of the variants of watch crystals available in today's market, provide a somewhat, incomplete answer. Plexiglass has something to say for hits and bumps and may even suit certain styles of watches, though still, lacks in sharpness and scratch resistance. Mineral glass, with all the added treatments, can be a worthy and economical substitute to sapphire, but ultimately, it is the sapphire crystal that demands the highest premium, and for the most part, remains the choice of luxury brands for their watches. There is no doubt, that the alternatives will continue to remain useful and relevant, as there is no doubt, that sapphire crystal will continue to serve as, the crowning jewel to luxury timepieces.