Simulation of “Opal” glass

by adrien

opal-simulation-d65

Opal glass is a strange material. It is a colorless glass that scatters blue light in the same way the earth’s atmosphere does it with sunlight: the sky is blue because blue sunlight doesn’t travels straight in large thicknesses of air, but in every directions. The sun appears yellowish because of the same reason: the blue part of the sun’s light spectrum has partly vanished from its rays under the form of blue sky.

In the opal glass, a very thin layer of diffusive “milky” glass containing very tiny particles is plated (“plaqué”) on the glass. Opaque white “flashed-glass” and opal “flashed-glass” are exactly the same material, but on the opaque version the layer of milky glass is very thick, up to 1 mm, while it can be maybe a 100 times thinner on very light opal glass.

It is very difficult to simulate the color of this glass on the computer: on the light table you see nothing but what seems to be a “cloudy” or “hazed” white glass. You need some distance to see the color appear, you need the light rays to pass in straight lines through  the glass otherwise the color won’t appear.

I did some research and I arrived to some pretty good results. The numbers under the pictures indirectly refer to the thickness of the milky layer. The left color is the one that appears by light transmission, the right one by light scattering.

This slideshow requires JavaScript.

When the layer gets really thick, transmission becomes zero and the glass is opaque and white.

not-ordinarytransmission

It’s really “white” but the light passign through it becomes yellow-brown.