Rust and Reflection: The Optical Properties of Oxidized Steel

In summary, the speaker burnished a rusty piece of steel using steel wool and noticed that it became smooth with no loose rust scale. The finish is similar to a century-old doorknob that has been rubbed by many hands. Despite not applying any oil or wax, the burnished rust appears darker and more reflective than before. The speaker wonders if this is a similar phenomenon to the darkening of wet objects, such as rocks, and questions why this happens.
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SkepticJ
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A couple of days ago I burnished a very rusty old piece of steel with a fine steel wool. It's now very smooth, and there is no loose rust scale. It has a finish somewhat like a century-old doorknob in some old building at a university. Some place where hands have rubbed it many thousands of times over the years.

No oil, wax etc. was applied to the piece, yet the burnished rust is much darker than it was before the process. Why is this? The rust is much more reflective than the matte it was. I can see the blue of the sky showing in the highlights, but the shades of the rust colors are much darker--darker than wet rust.

Is this a similar phenomena to the darkening that happens to wet objects? Some rocks, for example, look much darker when wet. I've noticed this in slate, for one. Why does this happen, as well?
 
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FAQ: Rust and Reflection: The Optical Properties of Oxidized Steel

What are the optical properties of rust?

The optical properties of rust refer to how light interacts with the surface of rust. Rust typically appears as a reddish-brown color and has a matte or rough texture, making it a relatively poor reflector of light. It also has a low transparency and does not allow much light to pass through it.

Why does rust appear to have a different color than the metal it is formed from?

Rust is formed when iron reacts with oxygen in the presence of water or moisture. This reaction produces iron oxide, which has a different molecular structure and composition than pure iron. The different molecular structure and composition of rust is what gives it a different color than the metal it is formed from.

How does the thickness of rust affect its optical properties?

The thickness of rust can greatly affect its optical properties. Thicker layers of rust can reduce the amount of light reflected, making the surface appear darker. Additionally, thicker rust layers can also reduce the transparency of the surface, making it appear more opaque.

Do different types of rust have different optical properties?

Yes, different types of rust can have varying optical properties. This is because rust can form in different ways, such as through exposure to different environments or from different reactions with other elements. Additionally, the composition and thickness of rust can also vary, leading to differences in its optical properties.

How can the optical properties of rust be measured?

The optical properties of rust can be measured using various methods such as spectrophotometry, which measures the amount of light absorbed or transmitted by a substance, or ellipsometry, which measures changes in the polarization of light as it interacts with a surface. These techniques can provide information about the color, transparency, and reflectance of rust surfaces.

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