A clear drinking glass has no obvious color, yet you can usually see where it begins and ends. Its rim catches the light, and the view through its curved sides looks slightly different from the view around it.
Those details help you notice the glass. Much of the light passes through, while some reflects from its surfaces or changes direction as it travels through it.
Some light reflects from the surface
When light reaches the boundary between air and glass, part of it reflects back. If that reflected light reaches your eyes, you can see a highlight or a faint reflection of something nearby.
This explains the bright streak on a glass beside a window. Move your head, and the streak may shift because you are viewing the reflection from a different angle. The glass itself can remain colorless throughout. Its surface is redirecting light from the room toward your eyes.
The background can reveal the shape
Light can also bend when it enters or leaves glass at an angle. This is called refraction.
Through the curved side of a drinking glass, a straight line behind it may appear displaced or bent. You are seeing the background through a material that has changed the light’s path. That distortion gives you clues about the glass’s shape, even where there is no bright reflection.
You can try this with an empty glass and a page of printed text. Look through its sides and notice where the letters change shape or position.
Shape makes a difference
A flat window with parallel surfaces usually lets you see the scene beyond with little distortion. A curved glass or a clear sphere can change that view much more noticeably. This helps explain why a clean window can be easy to overlook, while a glass ball draws your attention through its reflections and distorted background.
Our personalized photo crystals at 3D Heirloom add a portrait laser-engraved inside the clear material. The surrounding crystal remains transparent, so you can see the image within it alongside the reflections on its surface.
