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"I never knew till today," said Fred, "what a useful thing clay is. It is useful because it is pliable.
"You know we made a saucer and a basin with our pieces of clay?""Yes," said Norah, "here they are. I put them on the shelf.""Do you know," he said again, "that all our saucers and basins, and cups and jugs, and plates and dishes, are made of clay too?
"Yes, and so are the bricks and tiles and chimney- pots for building our houses, the drainpipes for taking away waste, and the flowerpots for our gardens.
"All these things are made of clay. Clay is earth. This is why we sometimes call the things earthenware.""What a useful substance clay is," said Norah. "I suppose all these things are molded into the right shape while the clay is moist and pliable. But how are they made hard, like this plate?""They have to be baked in very hot ovens." said Fred. "Bricks, after they are molded, are piled in a great heap, and a big fire is made in the middle of them. This fire is kept burning for weeks. When the baking is over, the things are hard and firm, and will always keep their shape.
"If we drop the cups and saucers on the floor they break into pieces. They are brittle as well as hard. The moist clay was not brittle, for we could throwit down, or even strike it with a hammer, without breaking it.""Did the baking make it brittle, Fred?"
"Yes, it did," said Fred, "and it did something more. The moist clay was pliable. But could I mold this piece of flowerpot into any other shape?""No," said Norah.
Willie, who had been very quiet for some time, joined in now and said, "Don"t forget, Norah, that the clay, after it is baked, will never be pliable again."SUMMARY
Cups and saucers, plates and dishes, basins and jugs are made of clay; and so are bricks, tiles, chimneypots, and ?owerpots. We call these things earthenware. While the clay is moist and pliable, the men mold it into the proper shape for all these things, and then bake them in hot ovens till they are hard.
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The children were called away before they could finish their chat about clay. They had to leave it till some other time.
The next evening Fred began by making a little rough basin with his piece of clay, just as he had seen teacher do. He then filled the little basin with water.
"I know what that is for." said Norah. "You want to prove that the moist clay is not porous."Fred then put a piece of dry brick into a basin, and filled the basin with water to the brim. They waited for a minute or two and then he said, "Look, Norah, some of the water has gone. What has become of it? It has not been spilt on the floor.""I suppose it has gone into the brick," said Norah. "That"s right," said Will. "Now what does thisshow?"
"If the brick has sucked up the water, it must be porous." said Norah.
"So it is," said Fred. "The baking made the clay porous.""Now listen," he added. "We want our bricks to be porous, so that any water that gets into them may drain out. But our cups and saucers, jugs and basins, and most of our earthenware things have to hold water. They must not be porous, or the water would run away.""But you told me they were all porous after they had been baked." said Norah.
"Don"t you be in a hurry, little sister," said Fred. "Here is a flowerpot, and here is a teacup. The teacup was as rough as the flowerpot at first, but it is smooth and shiny like glass now. We say it is glazed. This glaze is not porous, and liquids will not pass through it. After the cup is baked it is dipped into the glazing mixture and baked again. When it comes out of the oven this time it is smooth, shiny, and not porous, just as you see it now.""What clever boys you are," said Norah. "You are very good to tell me all these fine things."SUMMARY
Vessels made of baked clay are porous. Bricks and ?owerpots are porous. Cups and saucers, plates and dishes, basins and jugs are glazed, to make them smooth and shiny like glass. After this they are not porous.