Crystals and Reflections

The transparent cover above the dial is called the crystal, even when it is plastic rather than a crystalline material. Three separate questions matter: what it is made of, what shape it has, and whether its surfaces carry a coating.

Material is not shape

Sapphire is crystalline aluminium oxide. Optical-component maker Edmund Optics documents its high surface hardness and offers it with or without anti-reflective coatings. Scratch resistance is not the same thing as an assurance against every impact or damaged edge. Edmund Optics sapphire windows.

Acrylic gives another route to a transparent cover and is often used for a pronounced dome. That association is not a restriction: Sinn's 356 documentation describes domed sapphire made to match the profile of its acrylic version. You can therefore choose a domed silhouette without assuming that every real example is acrylic. Sinn 356 crystal construction.

Reflection versus tint

A dome changes the outline and the view of the dial at an angle. An anti-reflective coating instead reduces unwanted reflections at the surfaces. Some coatings leave a coloured residual reflection; blue is one possibility, not the definition of AR. ZEISS documents both blue and gold residual colours in its optical coatings. This is a coating principle, not a claim that those spectacle products are fitted to watches. ZEISS coating colours.

In the atelier

Flat sapphire, Domed acrylic and the AR sapphire option are bundled visual presets rather than independently selectable material, curvature and coating specifications. The AR option reduces the 3D reflection strength; its simplified rendering is not a spectral thin-film simulation. Compare them at an angle and keep the dial legible. The graphic does not certify optical transmission, coating durability, impact resistance or water resistance. A date magnifier is a separate date-display choice.

The cover follows the selected case opening in analog and digital designs. A shaped crystal does not stretch the rectangular electronic screen underneath it. A dome adds external height, not more internal room for a movement. Digital displays do not offer the analog date magnifier; compare their passive and illuminated views separately in the display guide.