The least expensive type of watch crystal is a form of plastic, made of the softest material of all three crystals. It is commonly referred to by several names, including Plexiglass, Hesalite, and Acrylic.
SAPPHIRE CRYSTALS VS OTHER WATCH GLASSES - EVERYTHING YOU NEED TO KNOW
WATCH CRYSTALS EXPLAINED
Protecting and displaying the face of a wristwatch is a thin clear cover that's typically referred to as the watch crystal. Watch crystals come in a myriad of shapes and sizes to fit the design of all the different timepieces being designed and sold. Crystals also come in varying thicknesses and quality. Watch brands today consider three attributes when selecting a crystal:
Clarity, Durability, Cost
Even with all the variations in size and so forth, watchmakers will use one of three distinct materials for their crystals, listed in order of least to most expensive:
1. Plexiglass (plastic), 1st image from the left
2. Mineral glass, 2nd image from the left
3. Sapphire glass, 3rd image from the left
The least expensive type of watch crystal is a form of plastic, made of the softest material of all three crystals. It is commonly referred to by several names, including Plexiglass, Hesalite, and Acrylic.
Pros of Plexiglass Crystals:
Cons of Plexiglass Crystals:
How do you know if a particular timepiece, or one you own, has a plexiglass crystal?
For the most part, you'll find plexiglass in vintage pieces. In cheaper watches though, it is also used for various 'tool' watches when an “unbreakable” quality is required.
Slightly more expensive, mineral glass crystals are used generally in wristwatches priced towards 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 of using mineral glass crystals are:
Pros of mineral glass crystals:
Cons of mineral glass crystals:
Expect to find mineral glass crystals on a wristwatch geared towards those on a budget. That doesn't make its use an indicator of poor quality overall as many high-quality timepieces use hardened mineral crystals.
How do you tell if a watch has a mineral glass crystal?
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 type of 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.
Pros of sapphire crystals:
Cons of sapphire crystals:
How do you tell if a watch has a sapphire glass crystal?
*Caution! If the crystal is mineral glass or plexiglass, you might end up with a crystal repair bill.
AR Coatings:
Sapphire crystal is more reflective than mineral crystal due to its higher index of refraction. (1,8 compared to 1,47). Applying one or more layers of AR (anti-reflective) coating will limit this reflection to a very low level. Very often, lines and marks on the top surface of a sapphire crystal are mistaken for scratches but are actually the scratched AR coating, or just AR coating wearing off after time. An AR coating on the inside of the crystal provides a good AR performance while avoiding this problem. If you do scratch a sapphire crystal, then it cannot be polished away and will need to be replaced.
Waterproof gasket:
As both mineral and sapphire crystals are extremely hard, they have little or no “flex”. This means that when the crystal is inserted into a hard, steel or titanium watch case, it requires a gasket to ensure a waterproof seal. These crystal gaskets are typically made of nylon, and are either flat, “I”-shaped or “L”-shaped. (see example above). The crystal is pressed into the case, using a crystal press tool. When it is pressed in, the nylon crystal gasket is “squeezed” between the crystal and the case rim, making a reliable waterproof seal. Over time, these crystal gaskets can become brittle and break, so it is a good idea to change the crystal gaskets every few years, to ensure the ongoing waterproof performance of your watch.
All of the options for watch crystals available today provide an incomplete solution, having their individual strengths and weaknesses.
All three materials have applications where their strengths make them the best choice. Even so, sapphire crystals will remain the "crown jewel" of timepieces for a long time to come. You just cannot beat sapphire when scratch resistance and clarity are demanded. In this case, Aiverc decided to use sapphire glasses with Anti Reflection Coating.
316L stainless steel
Sapphire glass with AR coated
PVD plated
Japanese miyota movement 2035
Quick release straps
Premium genuine leather
3D pressured dial
50 meter water resistance
2 year warranty
Source:
https://www.3watches.com/sapphire-crystal-glass-vs-mineral-glass/