HOW PORCELAIN IS MADE
"We'll go to the slip-house first where the clay bins are,"
Mr. Marwood said to Theo, "that you may start at the very beginning of
things. That is where the cars run in and unload the raw material."
They walked down a long corridor and rang for the elevator.
As the car shot to the basement Theo noticed a change in the
appearance of the factory. On every floor they passed there was a hum
of machinery and a glimpse of endless rows of china dishes; they stood
on shelves; they covered tables; they were stacked one within another
upon long counters.
"Some dishes, eh?" Mr. Marwood laughed, reading the boy's thought.
"I never saw so many in my life!"
"You will see many more before you are through," remarked his
companion.
The elevator brought up with a jerk.
"Here we are!" exclaimed Mr. Marwood. "At least this is our way into
the slip-house."
He led Theo through a passage and across a court into the adjoining
building.
Here a white powder covered everything. Men who hurried by in overalls
and caps were dusty as millers, their hands being coated to the finger
tips with dried clay.
Mr. Marwood stepped forward into the long, cement-floored basement and
pointed to the tracks embedded in it.
"It is on these tracks," he said, "that the cars come in and deposit
their contents in the bins. The bins are of a pretty good size, you
see. They measure about sixteen by thirty-two feet, and each one will
hold eight car-loads of clay. After the different kinds of clay are
unloaded and placed in their respective bins, the proper combination
for specific varieties of porcelain must be weighed out and mixed in
the 'blungers,' as we call the mixing tanks. Now this body formula, or
clay combination, is not entrusted to the ordinary workman. It is
kept secret. Therefore we have on the trucks that carry the clay
between the bins and the blungers what we call charging-scales, which
weigh automatically each ingredient in the compound without betraying
it to the loader."
"That is pretty clever," replied Theo.
"Yes, it is a very ingenious device," Mr. Marwood agreed. "The
blungers in which the clay is mixed are over there. You can see
them--those great machines near the centre of the floor. They are
heavy steel tanks lined with vitrified brick, and in the middle of
each one is a revolving contrivance, with steel arms and teeth that
grind the clay up very fine and blend it thoroughly. While it is being
mixed in this way water is added to it, and also a certain amount of
powdered oxide of cobalt to whiten it."
"Just as we put blueing in clothes," Theo ventured.
Mr. Marwood assented.
"This cobalt has already been pulverized and sifted most carefully, so
there will be no particles in it, and so it will readily
dissolve. After the clay mixture has had this mauling--for I can call
it nothing else--the blunged compound, or slip, flows in liquid form
into the sifter machines where it is strained through silk gauze or
else a mesh of fine copper wire."
"I shouldn't think you could ever strain such stuff," Theo declared.
"The sifters do get very hard wear," answered Mr. Marwood, "and are
the machines most liable to get out of order. They become clogged. Our
sifters are self-cleaning. By that I mean they have an attachment
which removes the waste obstructing them. Nevertheless, even with this
improvement they still bother us at times. If you watch this sifting
machine carefully you can see that the method is one of sliding the
slip back and forth until it is forced through the straining ducts."
"And then what becomes of it?"
They walked on and stopped before another machine.
"This is a rough agitator," explained Mr. Marwood. "Into it is pumped
the liquid slip you just saw strained, and afterward this is brought
in contact with a series of horseshoe magnets which extract from the
mixture every atom of iron."
"Iron?" repeated Theo.
"All clay has metals in it," continued Mr. Marwood. "Should you leave
any of these in a pottery clay they would cause you much trouble, for
when the ware was fired the metals would melt and discolor your
porcelain. Sometimes this happens with cheap chinas. I dare say you
yourself have seen dishes that are specked with yellow, or have stains
here and there. Sometimes you can also detect bluish particles. That
means the cobalt has not been properly ground or sifted. In less
expensive wares such defects are frequent. But there is no excuse for
them when making fine quality porcelains."
Theo listened attentively.
"After this iron has been extracted," went on Mr. Marwood, "the slip
passes into smooth agitators, where it is simply kept well stirred in
order that the heavier ingredients in it may not settle to the
bottom. Then the liquid is forced by means of a slip-pump into the
filter-presses, and it is now that you begin to see an approach to the
clay used for shaping dishes. Up to this point the slip has been only
a thick creamy substance. Now the filter-press squeezes this through
canvas bags until after having been pressed between iron plates you
get your cakes of smoothly mixed clay of about the consistency of
putty. Each cake is of regulation size, and it is supposed to be an
inch-and-a-quarter in thickness, and to weigh forty-two pounds."
"The clay is now ready for use?" Theo asked.
"Practically so," was Mr. Marwood's reply, "although before it can be
sent to the jiggermen to be modeled it must pass through the pug-mill
to be made more plastic and workable. It is here that it gets its
final kneading, all the air bubbles in it being eliminated by a series
of steel knives."
"I must say it is pretty thoroughly prepared," smiled Theo.
"It has to be," was Mr. Marwood's grave reply. "Each of these details
is an important factor in the making of high grade porcelain, and
should any of them be omitted we should get no flawless ware. It was
this infinite care in preparing clay that gave to China, Japan,
France, and Germany their perfect results in porcelain-making. If we
would equal what has been done in the past we must be just as
painstaking, and neglect no detail. As a nation we Americans are far
too prone to dash ahead and expect results all in a minute. We do not
like to mount a stairway step by step; we wish to shoot to the top in
an elevator. Now you cannot manufacture porcelain, or for that matter
anything else, in such a fashion."
"I know it," replied Theo. "Dad says we hurry so much over the little
things that we turn out quantities of poorly made goods that are just
hustled through instead of being carefully finished."
"Your father is right," Mr. Marwood admitted. "It is far too often
quantity and not quality with us. Just so long as men are paid on the
piece-work system we shall not better the condition, either. It
stands to reason that a man who is rushing to make as many objects of
one kind as he possibly can in an hour is not going to take the pains
to finish them very carefully. His daily bread depends on his
hurrying. Not a second can be lost. It is an unfortunate labor
condition, and one that I hope to see remedied some time."
The elder man smiled.
"But we must not take time now to go into labor problems," he
added. "In our day they are absorbingly interesting and one might
spend hours discussing them. What we all are eager to do is to see
them readjusted until they shall be fair to all parties."
"That is what Mr. Croyden wants," put in Theo.
"I know it is. He is heart and soul in this mill and his
employees. All the time he is working to improve conditions here. Now
we must go on, or we shall not get anywhere. To return, then, to our
clay; it is now ready to be carried to the floor above on elevators
and handed over to the potters."
"Are the ingredients for the glaze prepared in the same way?" Theo
inquired.
"Partially so. The formula for the frit and glaze is also a secret
one. Usually the frit, a material similar to glass, is crushed to
powder beneath stone rollers called chasers. Water is then added and
the compound turned into the grinding-mill where it is ground for an
entire day. Sometimes, however, a different process is preferred and
the material is put into a kiln and melted instead. In either case it
must finally be worked into a smooth liquid which can be strained
through fine lawn. It is then sent to the agitators and constantly
stirred until it can be pumped into the storage tanks in the
dipping-room."
"That is just what I wanted to know," said Theo.
"Any more questions?"
The boy shook his head.
"Not now, thank you."
"Then as we have finished here shall we go up to the clay-shop?"
"Yes, I am ready," Theo affirmed. Then as if confronted by an
afterthought he asked:
"Is the porcelain made here bone china or ----"
"Spar?" put in Mr. Marwood as the lad hesitated.
"I don't think I understand."
"Feldspar."
"Oh, then I know," cried Theo. "I did not realize you classified
porcelains as bone or spar."
"We do," was the quick reply. "Our finest grade of porcelain has
little or no phosphate of calcium, or ground bone, in it. But it is in
consequence very costly, and therefore to meet the demands of the
market we also manufacture a porcelain slightly strengthened with a
bone element. Nevertheless this is composed of such a wonderfully
blended body that it is as exquisite as any of the most beautiful
English wares. Personally I prefer it to a pure feldspathic china."
"My questions are all answered now," laughed Theo. "Shall we go up to
the clay-shop?"
They rang for an elevator and stepped in.
"Next floor, O'Keefe," said Mr. Marwood to the operator. "I am going
to teach this lad how to make dishes."
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