Though the term blackboard has a color right there in its name, most of them aren’t actually black. While we still use the term more or less interchangeably with chalkboards, blackboards tend to be green. Why the difference? Why call a surface a blackboard if it's green?

Because 200 years ago, blackboards were black. According to author Lewis Buzbee’s Blackboard: A Personal History of the Classroom, large boards of connected slates that teachers could write on for the whole class to see didn’t come around until the early 1800s, and the name blackboard wasn’t used until 1815. They were made with slate, or in rural areas, they were often just wooden boards painted dark with egg whites mixed with the remains of charred potatoes. Later, they were also made of wood darkened with a commercially made porcelain-based ink. They were, true to their name, black.

And the relatively affordable, ubiquitous technology was a huge success, changing education forever. By the mid-19th century, even the most rural schools had a blackboard.

As an 1841 teaching manual, The Blackboard in the Primary School, put it: “The inventor or introducer of the black-board system deserves to be ranked among the best contributors to learning and science, if not among the greatest benefactors of mankind.”

In the 20th century, blackboards began to look a little different, though the idea was the same. In the 1930s, manufacturers began to make chalkboards using a green, porcelain enameled paint on a steel base. By the 1960s, the green chalkboard trend was in full swing. Teachers had discovered that a different colored paint was a lot more comfortable to stare at all day, because green porcelain paint cut down on glare. By and large, many blackboards were slowly replaced by their green brethren. (Apparently, greenboards wasn’t quite as catchy of a name, though, so the term blackboard stuck.)

But today, many school children might not be familiar with either blackboards or "greenboards." In the 1990s, schools began converting their classrooms to whiteboards, which produce less dust (and eliminate that terrible screeching noise). According to The Atlantic, at the turn of the millennium, whiteboards were outselling chalkboards by a 4-to-1 ratio.

You can still find the occasional blackboard in a classroom, though—even if it’s just decorative. And some schools are rediscovering blackboards, literally. In the summer of 2015, construction workers renovating an Oklahoma school for smart whiteboards found two historic slate blackboards that still bore drawings from almost 100 years ago.

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