Humans have been using steel for about 10,000 years. Stones, bones, and wood were the principal tools until that point, but metal is more fluid and malleable. Metal becomes soft when heated and hardens when it is compressed. It can be hammered into different shapes and is almost endlessly reusable. It was fundamental to the success of the Industrial Revolution.
As long as it’s been around, it was only in the twentieth century that we began to understand steel better. Steel’s actually comprised of crystals. We don’t often think of metals in this way. When we hear crystal, we usually think of quartz or diamond—the larger, transparent minerals. But the crystals that make up metals like steel are microscopic and opaque. A stainless steel razor blade will contain billions of these. They form almost-perfect three-dimensional shapes. Bonds between the atoms maintain the structure and give steel its strength. When a person shaves, infinitesimal crystals are chipped away, disrupting the uniform pattern along the razor’s edge.