Blackboards

Press, 10 November 1981, Page 22

Blackboards

What would school be like if we didn’t have blackboards? Think of the hours we spend during our school days, either writing on the blackboard, or reading what the teacher has written on it. But what is the blackboard made of?

Many people know it is made of a substance called slate. But what is slate?

Interestingly enough, slate is a material that is millions of years old. It all began when particles of clay gradually sifted down to the bottoms of seas and lakes, a long time ago. As they lay there, at the bottom of the sea, they slowly formed a soft mud.

As time went on, this mud hardened, and became a kind of rock-mud called shale.

The earth was still going through changes, and at one time the crust heaved upward in that part where the shale was. The layers of shale were folded up into small ripples. The other

rocks the shale so hard that it became slate. Because the original clay particles that made up the slate were deposited in layers at the bottom of the sea, the slate that finally developed has layers, too. This is one of the reasons slate is so useful for so many purposes. It not only makes blackboards, but it is also used for roofs of buildings and sinks. Slate is taken from quarries or from underground mines in big blocks, which are divided into smaller blocks, before they are removed to be split. In making a piece of slate, the splitter takes blocks about 7cm thick. He holds a chisel in a certain position against the edge of the block, and taps it lightly with a mallet. A crack appears, and by using the chisel the block is split into two pieces with smooth and even surfaces.

The splitter keeps on doing this until he has changed the original block into about 18 separate “slates.”