The Story of Glass

by Sara Ware Bassett

"Oh, yes, I see. And where have they taken the pitcher now?"

"We will follow it," replied the foreman.

Escorting them across the room he showed them a low oven or kiln. The door of it was open, and inside they could see all sorts of glassware which had just been finished.

"Here is where your pitcher will remain for the next three days," said he. "We build a fire, put the completed glass in the oven, and leave it there until the fire goes out and the oven gradually cools; we call the process annealing. It prevents the glass from breaking when exposed to friction or to the atmosphere. Glass is very brittle, and extremely sensitive to heat and cold. If it were not annealed it would not be strong, and would snap to pieces the moment it came in contact with the outer air. Now it is very difficult to anneal glass, the trouble being that all hollow ware is one temperature on the inside and another on the outside. Hence, when heated, the inside takes longer to cool. Any current of cold air that strikes it will fracture it. So, as you can readily see, an annealing kiln or oven must be arranged in such a way that it will allow the two surfaces to cool simultaneously."

"I think I understand," answered Jean. "And you say these things must stay in the kiln about three days?"

"Yes, the kiln takes about that time. It is a slow process, because we have practically no way of regulating its heat. A lehr does the work much quicker. Over here you will see one. It is a long arch or oven open at both ends. The glassware travels in iron pans along a moving surface from the hot oven, or receiving end, to the cool, or discharging end. The temperature of the lehr can be scientifically tested and regulated, and this is very necessary, because the heavy glass intended for cutting can stand a greater heat than can ordinary hollow ware such as vials and table glass. We regulate the oven according to what we are annealing in it. It does not take so long to anneal glass in a lehr as in a kiln, and therefore in many factories only lehrs are used. If you will come around to the cool end you can see some of the finished pieces being taken out. Each object is made by a certain set or gang of workmen—a shop, we call it. The work of each shop when taken from the lehr is put in a box by itself and is then counted up, and the men paid according to the number of perfect objects finished. It is piece work. For instance, one shop makes only pitchers, another wine-glasses, another vases, and so on. Every group has its specialty, and each workman in the team understands exactly what his part is in the whole. The common interest of turning out as many perfect pieces as possible spurs each man to work as rapidly, well, and helpfully as he can."

"Just like a football squad, Uncle Bob," laughed Jean.

"Exactly," nodded Mr. Wyman. "After the finished glass is taken from the kiln or lehr it goes to the examining room, where girls dip it in clear water and hold it to the light to test it for imperfections; then it is sorted, packed, and shipped."

"And vases, sugar-bowls, tumblers, and most of the hollow glassware is made in the same way?" inquired Mr. Cabot.

"Yes, practically so. The general scheme is the same. As I told you, there are some difficult designs which must be squeezed into shape in moulds. These are of iron, and for the convenience of the blowers are set in holes in the floor. They are made in two parts joined by a hinge. The molten glass is blown to the approximate size and then a boy shuts it inside the mould and the blower blows into it until it has entirely filled out the mould in which it is confined. When released it is shaped to the form required."