Gloss (optics)

Have you ever wondered why some objects shine while others look dull?

This quality is called gloss. It describes how well a surface reflects light in a mirror-like way. This specific type of reflection is called specular reflection.

When light hits an object, it can do several things. It might be absorbed, which helps create color. It can pass through a surface if it is clear. It can also be scattered in many directions, which is called diffuse reflection.

Gloss happens when light reflects at a symmetrical angle to the incoming light.

How a surface looks depends on its texture and its material. A very smooth or highly polished surface creates a lot of specular reflection. This makes the object appear shiny to your eyes. A rough surface scatters the light in many different directions instead. This makes the object look dull and the reflections look blurry.

The type of material also changes the effect. Metals reflect a high amount of light at any angle. Non-metallic materials, like plastics, might absorb some light depending on their color. This can change how much light is reflected at different angles.

People have studied how we see gloss for a long time. In 1914, Leonard R. Ingersoll began studying how gloss affects paper. He even made a tool called a "glarimeter" to measure it. He used a special method to separate shiny light from scattered light. Later, in the 1930s, A. H. Pfund studied how we perceive shininess. He found that gloss is about contrast.

He noticed that a black surface can look glossier than a white one. This is because the bright light stands out more against the dark background.

In 1937, R. S. Hunter described six different ways we see gloss. One is called sheen, which is shininess seen at low angles.

Another is contrast gloss, which compares shiny areas to dull areas. There is also distinctness of image gloss, which is how sharp a reflection looks. Scientists also look at the absence of bloom to see if a reflection looks cloudy.

To measure these, people use a tool called a glossmeter. Most studies use a 60-degree angle because it matches what our eyes see best.

Today, many industries use standard rules to measure gloss. The ASTM organization created a standard test method in 1939. This helped make sure everyone measured gloss in the same way. Different industries use different angles for their tests. The paper industry often uses a 75-degree angle for coated papers. The paint industry uses an international standard called ISO 2813.

These rules help makers ensure that everything from cars to books looks just right.