Glossmeter

1914 Glossmeter

The book of science

Tom Sharp

Leonard R. Ingersoll optics Glossmeter

Glossmeter

Leonard R. Ingersoll figured, since glossiness of a surface does not correlate well with its mechanical smoothness, an optical method to measure gloss was best. The Ingersoll Glarimeter compares specularly reflected light where the light-source is at a sufficiently low angle of incidence to cause the light at the angle of reflection to be plane polarized, with diffusely reflected light, which is reflected in all directions. The view through the Glarimeter eyepiece shows a divided field of view. Diffusely reflected light is shown through a smoked glass to the top, and specularly reflected light through a Nicol prism to the bottom. The operator turns the viewport until the line between the two parts disappears. The degree of rotation correlates with the glossiness.

Specular reflection is polarized

Glossiness is an optical not a mechanical property of surfaces. Color diminishes the amount of diffusely reflected light but not the amount of specularly reflected light. In specular reflection, light is polarized. A paper with an ideal matte surface, reflecting light only diffusely, combined with a dead-black ink, is most readable.

Calendering

Calendering paper puts it through rollers to improve its smoothness. Wandering dervishes refuse to be calendered, although we call them calenders.

Leonard R. Ingersoll did his work under contract with the Department of Agriculture, so he could not claim royalties for his Glarimeter,

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