Thanks!Special thanks to Paul Leichtnam and all the
other nice folks at the Lenox china factory in Kinston,
NC, for helping us out with this
article.
|
When
selecting tableware for your house, you have a number of
choices: earthenware, stoneware, and porcelain. Among
porcelain products, you've got basic porcelain, fine china and
bone china. Many well appointed homes stock at least one, if
not a combination of two or more of these options. In fact,
one of the oldest standing customs for a bride and groom is
registering for a china pattern.
Lenox china factory in
NC
|
No
matter how elaborate or lovely the place setting, when it
comes down to it, you're usually more concerned about what's
being served on the china, rather than the china itself. But
if you ever stopped to consider how china is made, you'd be
amazed -- it's actually fascinating.
In this edition of HowStuffWorks,
we'll go behind the scenes at the Lenox factory in Kinston,
NC, to see how bone china is made.
China Basics
People have been making and
using porcelain products for a very long time. Around
the end of the 18th century, an Englishman named Josiah Spode
developed a new formula for china that incorporated the use of
calcined bone ash. The addition of bone ash in china
mixtures continues today at Spode as well as many other china
manufacturers, including Lenox.
Lenox is the only manufacturer of bone china in the United
States. Considered by most to be the finest of porcelain
products, bone china is stronger and more translucent
than the basic porcelain and "fine" varieties.
Display of various china patterns in the
Lenox
lobby
|
Creating
bone china entails an involved series of steps carried out by
a number of highly skilled individuals and some really
impressive machinery. When you first enter the Lenox factory,
you're immediately struck by the size of the facility (about
150,000 square feet, 14,000 square meters) -- it takes a lot
of space to accommodate all the equipment and the 350-member
staff. Although this factory only produces bone china, what
we'll find here is generally useful information because other
porcelain products are made in pretty much the same way.
There are four main processes involved in creating china:
- Clay making
- Mold making
- Glazing
- Decorating
Another thing that stands out as you tour the Lenox
facility is that all of these processes rely on the four
elements. As you'll see in the next several sections, earth
(the raw materials), wind (there are air hoses everywhere),
fire (the kilns), and water (used during every process) are
all required to make china.
|
Presidential
PlatesLenox has made the
presidential china for five United States presidents:
|
Making the Clay
The clay making
process begins in the batch-house. Pulleys hoist giant
metric-ton bags of raw materials from pallets located on the
factory floor. They are raised up to a platform about a story
high. The bags are then left to hover over enormous
hoppers into which their contents will be emptied.
Supplies
|
Two bags of china clay hover over giant
hoppers.
|
From the hopper, the dry raw materials move to a high-speed
blundger, where the materials are mixed with water to
form a slurry. These slurries, stored in colossal
tanks, will later be blended together to form the final
mix and slip.
There are five main dry ingredients that go into the final
mix:
- Bone ash
- China clay
- Ball clay
- Flint
- Feldspar
These raw materials are both
domestic and imported products. For example, the feldspar used
at this plant comes from North Carolina, while the bone ash
comes from Holland and the United Kingdom.
Lenox creates two colors of bone china. The sale of white
china products comprises about 80 percent of its total sales;
ivory-colored china makes up the remaining 20 percent.
Although certain additives or pigments are necessary to get
the ivory color in the finished product, in the slurry state,
both clays appear to be slightly gray. To differentiate the
final mix for the ivory from that of the white, green
vegetable dye is added to the ivory mix. The vegetable dye
will eventually burn out in the kiln. If the dye isn't added,
there's no way to distinguish one clay from the other. It also
helps to avoid getting the two clays mixed together.
During the clay stage, which is any time before glazing,
all scrap clay that hasn't been contaminated by debris
(perhaps it was dropped on the floor and picked up some lint)
can be reclaimed. In fact, every finished product here
is made from 80 percent virgin clay and 20 percent reclaimed
(scrap) clay.
Slurry for ivory china (left) and a holding
tank for ivory slurry
(right)
|
After the final mix has been prepared, it is pumped to a
filter press to remove air and water from the mix --
the moisture level is reduced to about 20 percent. Final mix
left in a liquid state is referred to as slip. We'll
talk more about slip later in this article.
The sheets of clay that are formed in the filter press are
then passed through an extruder to remove more air and
change the flattened squares to a tube shape. These tubes are
referred to as pugs. Resembling a really huge piece of
chalk, each pug weighs in at a little more than 30 pounds
(13.6 kg).
Sheet of clay (left) and extruder
(right)
|
Pug
machine
|
A robotic arm called a pug stacker collects the pugs
and stacks them in a pyramid on pallets covered with plastic
sheeting. The sheeting looks a little like the plastic wrap
you would use in your kitchen, except that it's super-thick.
Rolls of plastic sheeting hang on a wall nearby. Pieces are
torn from the roll to cover the pyramid of pugs. The bottom of
the plastic is tucked along the underside of the bottom row of
pugs, forming a protective tent to maintain the
humidity level.
Some pug stacks are marked "for cups only." The moisture
content of these pugs is at about 15 percent rather than 20
percent.
Molds are used to transform the pugs and slip into plates,
cups, bowls, pitchers and other china pieces. Let's take a
look at how these molds are created.
Creating the Mold
The mold-making process is
an integral part of china production.
|
Mold
FactsEach plaster
production dinner plate mold should get about 100 uses,
while molds for serving pieces and more intricate items
can only be used about 10 to 15 times.
If you're wondering why they don't just use the metal
molds, it's because the plaster does something metal
cannot do -- it helps draw out moisture from the
clay!
|
Large
metal master molds and plaster are used to make
production molds. For dinner plates, the metal master
molds look something like two automobile hubcaps sandwiched
together.
To create a production mold, large bags of plaster are
mixed with water and then funneled into a big mobile bucket
that hangs overhead. Meanwhile, the metal master molds are
prepped by spraying a soapy mixture inside. This
residue will help with the release of the production mold
later. The metal molds are lined up, one after the other, on
three rows of tables. Each mold sits on top of something that
looks like a lazy Susan (a disc-shaped piece of wood that
spins).
This metal mold is prepped and ready to be
filled. Notice the finished production plate mold on the
right.
|
The aerial bucket is used to fill the metal molds
with thick, creamy plaster. This takes two people. One person
pours while the other person spins the metal mold to make sure
the plaster is distributed evenly.
Pouring the plaster
mold
|
Ready to be
released
|
It takes about 20 minutes for the plaster to set. A rubber
mallet is used to loosen the plaster production mold by
tapping along the outside of the metal. The mold is released
when the two halves are pulled apart.
Air hoses are used to spray plaster bits out of the metal
molds and to clean off the plaster molds, removing any excess
plaster dust or particles. At a nearby table, someone inspects
each mold and stamps it with the day's date. This helps track
the number of times each mold is used.
Something like 300 molds are made in this factory every
day. These molds are used in one of two ways: either with the
clay pugs or with the slip.
Forming a Plate
The forming operation, or
pug molding, starts at the jiggering unit. Like most of
the machinery here, there are two jiggering units: one for
white china (gray pugs) and one for ivory china (green pugs).
The pugs are pushed through another extruder to remove any
remaining/excess air. A giant slicer divides each pug into
several clay discs.
Each disc of clay is then placed on top of a plate mold.
The plate mold begins to rotate. A jigger head hovering
above starts to rotate, too, and presses down upon the
rotating pug slice and mold plate. A scraping tool cuts off
excess clay from the rim of the newly formed greenware
plate.
Pug slices are placed on production
molds.
|
A plate is formed: Note the excess clay
traveling down the conveyor belt to the yellow recycling
bucket.
|
The excess clay shoots down a conveyor belt to a recycle
bin. This reclaimed clay will be blended with water to create
a slurry that will eventually go into a batch of final mix.
The greenware plates are passed through a mold dryer, then
removed from the mold and passed through a second dryer -- at
this point, the clay has gone from a 20-percent moisture level
to a 0.5-percent moisture level. The plates move through a
finishing machine so that damp sponges can finish, or smooth
out, the edges of each plate.
Workers inspect each plate as it leaves the finishing
machine. The plates are placed on setters. Setters are
actually very similar to the plaster molds, except they're
made of material that can withstand the extreme temperatures
of the kiln. The setters, now carrying the newly made plates,
are stacked on metal racks to be passed through the kiln. The
setters play an important role. At this point, the plates are
still fairly malleable (they can bend). The setters ensure
that the plates maintain their form in the kiln.
A Lenox employee places a plate on a
setter.
|
There are separate machines for molding cups, mugs and
small bowls. The cups move through a jiggering unit similar in
concept to the plate unit. As mentioned earlier, the pugs used
for cups are at a 15-percent moisture level. Once the basic
cup form is made in the jiggering unit, it is put through the
profiling unit. A carbide blade forms the side and foot
profile of each cup.
Handles are affixed, by hand, to each freshly profiled cup.
These cups are then passed to a finishing area. Using small
finishing knives, water and sponges, workers smooth out the
lip and foot of each cup and make sure the handles are
securely attached. The finished cups are placed on small
setters, called chums, and stacked on racks destined
for the kiln.
Now, let's take a look at the casting process: forming
china from molds and slip.
|
Cross-trainingIn stations like this, there are several jobs to
be done. All station employees are cross-trained on the
various aspects of work done in that particular unit.
This benefits both the company and the employees.
For the company, cross-training helps ensure
continued productivity, even in the absence of employees
due to vacation or sick time. For the employees,
cross-training can help lessen physical strain. Some
jobs require close work that can cause eye
strain, while other jobs require long periods of
standing -- so switching tasks mid-shift makes a lot of
sense. |
Casting
In the casting area, 18 small lazy
Susans sit on top of a conference-sized round table. Upon each
of the 18 discs rests a casting mold. Three hoses hang from
the ceiling: one for air, one for white clay and another for
ivory clay. These hoses are used to fill each mold with liquid
clay or slip.
These four-piece molds are used to make small
pitchers.
|
Slip and air
hoses
|
The casting process basically works like this:
- You use the air hose to clean out the mold, making sure
there's no excess plaster or remaining slip from a previous
fill.
- You aim the nozzle of the hose and fill the mold with
the desired slip (white or ivory).
- You allow the slip to set for about 10 to 15 minutes.
- You pour out the excess slip and let the mold sit for
about another 10 minutes.
- You release the mold.
To release the mold, the giant red bands are removed and
the four mold pieces are gently pulled away from the clay
piece inside.
Because the mold is in several pieces, there are seams
along the greenware where the molds fit together. Workers use
damp sponges and finishing knives to smooth out the surface
and remove the seam marks.
Raw clay pieces that have not been fired in the kiln are
referred to as greenware -- not to be confused with the
green-colored clay pieces that indicate an ivory finished
product. Fired pieces are called whiteware. Once the
greenware is complete, it's ready to be fired in the kiln.
Cool
Facts!
- A 12-inch (30.5-cm) greenware plate will shrink to
10 inches (25.4 cm) after being fired in the kiln.
- The Kinston plant uses about 4 million pounds (1.8
million kg) of clay each year.
- The Kinston plant can produce 15,000 to 20,000
pieces of china every day.
- Lenox now makes some gilded china that's safe for
use in a microwave.
- From dust to dish, it takes about three or four
days to create a piece of Lenox bone china.
|
Firing
Once the greenware pieces (either
from the pug molding or slip molding process) are finished,
they're stacked on metal racks and sent to transportation
lanes (holding areas). Eventually, they'll be moved to and
passed along a conveyor belt through the bisque kiln.
This gas-fired kiln, which is 135 feet (41 meters) long, runs
in nine-hour cycles, meaning each piece of greenware is fired
for exactly 9 hours. The temperature inside this kiln is 2,290
degrees Fahrenheit (1,254 C).
Racks of setters laden with greenware dinner
plates enter the
kiln.
|
The temperature inside this kiln is a
whopping 2,290 degrees
F!
|
After the whiteware is removed from the kiln, each piece
gets a bath. Smooth stones and water are used to polish each
piece of china -- the vibration of the stones smoothes away
the rough exterior (pieces fresh from the kiln feel a little
like very fine-grained sand paper). This process is called the
vibratory finish.
Stone
bath
|
Shiny!
|
After the stone bath, the whiteware is run through a giant
industrial dishwasher and dryer. At the other end, each piece
of china is closely inspected for any damage or flaws. Pieces
that pass muster move on to the glazing process.
Glazing
China isn't something you think
about every day. In fact, if you're like many folks, you
probably only use the good stuff for special occasions. People
often do this because it seems so delicate. As it turns out,
china is actually a lot stronger than you would think -- a
whole lot stronger. Some clever marketing people at a large
department store in Canada decided to show folks just how
strong the good stuff can be by supporting the entire weight
of a Lola
race car on top of four Wedgewood
teacups!
So, what makes china so strong? We've already mentioned one
thing: The bone ash in bone china makes it stronger than other
porcelain products. Another thing is the glaze. Think of it as
liquid glass that, once heated, forms an incredibly strong
protective shell. The glazing process at Lenox is very
interesting to watch.
Each piece of china must be pre-heated so the glaze will
adhere to its surface. The glaze is pumped from giant holding
tanks to the glazing area.
Notice the glowing orange area to the right
-- this is where the dishes are pre-heated prior to
glaze
application.
|
Pre-heat
|
Bearing a slight resemblance to an automated car
wash, the glazing booth contains something like a dozen
spray guns. For the dinner plates that are being glazed, eight
of these spray guns are in use so that every part of the
plates will be covered. The plates, resting atop metal stands,
are pushed through the continuous stream of glaze. A wall of
flowing water (it looks like a series of waterfalls) faces the
row of spray guns.
Glazing
unit
|
This series of waterfalls serves an interesting and thrifty
purpose. The water catches the mist of glaze that doesn't fuse
to the clay. The great thing about this is that it turns out
the glaze is heavier than the water. So, after the water from
the glazing booth is left to sit for a while, the glaze can be
reclaimed and recycled for future use.
Prior to being placed in the gloss kiln, which is 185 feet
(56 m) long, the foot (bottom) of each piece of china must be
wiped clean with a damp sponge so it won't stick to the kiln.
This kiln runs for eight and a half hours at 2,020 degrees
F (1,104 C). Unlike the first kiln, which is all gas, this one
uses both gas and electricity.
Big
Bill!The Lenox plant
in Kinston, NC, spends 1.5 million dollars on gas and
electricity each
year.
|
For most
kilns, there's a warm-up stage, a hot-zone or soak stage, and
a cool-down stage. In the gloss kiln, the stages go basically
like this:
- Three or so hours for ramp-up
- Two and a half hours of soak
- Three hours of cool-down
During soak, there's a lot of turbulence in a gas kiln.
Because an even finish is needed for the glaze, the soak stage
of the gloss kiln is powered by electricity.
Stacks of setters and plates enter the
glazing
kiln.
|
Plates, soup bowls and tourines exit the
glazing
kiln.
|
Notice the shine on these freshly glazed
pieces.
|
After the gloss kiln, the whiteware is inspected again. Any
sharp or uneven edges on the foot of the whiteware are ground
on a diamond wheel.
Grinding the foot of a
plate
|
The whiteware is now ready for decals and decoration --
until then, it's kept in a holding/storage area.
Decorating with Style
With about 85
different patterns and something like 400 shapes to cover,
decorating the china can be a time consuming and tedious
process. Depending on the shape of the piece and the detail
involved, some processes require a personal touch while others
are done by machine.
There are three things that can be applied to adorn a piece
of china:
- Decals
- Precious metals, either gold, platinum or a
combination of the two
- Enamel
Decals can be applied by hand or machine. When a decal is
to be applied by hand, to a plate, for example, a thin, blue
line is drawn around the edge. This line will be used as a
guideline for the decal that comes next. The blue ink
eventually disappears; it burns away in the kiln. The decals
are soaked in water and then placed, by hand, on the plate.
Using a slightly damp sponge, the decal is smoothed onto the
plate. Once the decal is in place, the plate is flipped over
so the Lenox back-stamp (actually a decal made of gold) can be
applied to the bottom of the plate. The pigments (and
sometimes metal) of the decals are sealed into the whiteware
in a kiln running at 1,600 degrees F (871 C) for about two and
a half hours.
The Lenox back-stamp is applied to the
underside of a
plate.
|
This stack of decals and back-stamps will
soon be applied to a nearby stack of
dishes.
|
The metal rims shown here can be applied by
machine.
|
The
process of applying precious metal (gold or platinum) to
whiteware is referred to as gilding. Like the decal
application, this can be done by hand or by machine.
For pieces like creamers and cups, a human touch is best.
The metal, which is in a liquid state, is painted on each
piece with a delicate brush. For other pieces, such as dinner
plates or platters that are to be edged in a wide rim of
metal, a machine can handle the job.
No matter what the application, the metal is permanently
formed to the china in a kiln running at 1,400 degrees F (760
C) for about one and a half hours.
Painting on the
metal
|
When enamel is applied, the design will ultimately look
embossed on the plate. Enamel is applied either by hand or by
a machine that stamps an entire design on the china. At first
glance, the by-hand application looks pretty simple, sort of
like writing with decorator icing.
Applying enamel by
hand
|
It turns out, though, that it's a lot more difficult than
it looks. The work requires patience and a very steady hand.
For the plate shown below, close to 400 dots of enamel must be
applied to complete the decoration.
With a decal and gilding in place, 390 enamel
dots must now be added to this plate to complete the
pattern.
|
The machine used to apply enamel decals is one of the
coolest things we got to see at the Lenox plant.
Unfortunately, its many moving parts are encased in a glass
box, so photographing them was difficult. But here's how it
works:
- The decal, covered in a waxy residue, is heated.
- A giant silicone rubber bomb (looks like a huge, red,
rubber kickball, except it's cone-shaped on one side) is
squashed onto the decal.
- As the bomb is lifted, so is the decal.
- The bomb is squashed against a plate, transferring the
decal to the plate.
This pink enamel decal was applied in the
heat-release
decal
machine.
|
After the enamel has been applied, the china must go
through a 1,400-degree kiln for about one and a half hours.
Once the decorating is complete, the china is ready to
packaged.
Going to Market
Now
that the china is completely decorated, it's ready for final
inspection and packaging.
The finished pieces of china are moved out of the
decorating area and are inspected one last time. China that
passes muster will be bar-coded,
wrapped in foam and bagged.
The bagged china will then go to a boxing area and be
passed on to shipping.
Plates being inspected and
bar-coded
|
For a piece that isn't perfect, one of three things can
happen:
- It will be destroyed.
- It will be marked as a "second" and sold in a special
outlet store.
- If the imperfection can be fixed (maybe an area is
missing a bit of gilding), it will be fixed and sent through
the final inspection process again.
Caring For Your China
Most china
manufacturers agree that their products are created to be used
-- even every day! With proper care and storage, your china
should bring you years of dining pleasure. The Lenox
Web site offers the following tips:
- Leave the abrasive powders, liquid detergents, and steel
wool scrubbing pads for your pots and pans. Mild detergents
and gentle cleansers are best.
- For sink washings, line the basin bottom with a cushiony
towel or rubber mat, and use a soft sponge or cloth on the
china.
- Although hand-washing is preferred, you can use the
dishwasher. When using the dishwasher, choose a regular or
gentle cycle. The "pots & pans" cycle is not
recommended.
- To avoid chipping or cracks, load the dishwasher so that
the china cannot knock into or bump other pieces of
dinnerware, and make sure the china is adequately cooled
before unloading it from the dishwasher.
- If stacking is a necessity when storing your china, use
felt pads, napkins or even coffee
filters to separate each dish. This will keep the foot of
each plate from abrading the plate under it.
For even more information on bone china, fine china and
other porcelain, check out the links on the next page.
Lots More Information!
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