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When I was asked to write a history of ceramic tile
in the United States I took a long time thinking about
how to approach the subject. Ceramic tile has a long
history. Probably no one knows the actual beginning
but tile has been around for a very long time. I remember
how impressed I was with the tile still in good condition
in the ruins of ancient Rome. The tile in Pompeii is
still in excellent shape after 2000 years, although
it was buried in volcanic ash for much of this time.
Recently a kiln was unearthed in Centamura del Chianti,
near Siena, Italy from the 3rd century b.c.e. Broken
pieces of ceramics were found in the ruins of the kiln.
These were surmised to have been offered to the god
of the kiln to bless the outcome of future firings.
Making ceramics was a hazardous and speculative business
in those days. But this article is about the more recent
past where the outcome of the firings is much more predictable.
North American tile making had its roots in Europe
where tile had been manufactured for years. Tile artisans
brought this craft with them in the 1800's and set up
tile making factories all over the country. Tile was
largely made by "batch firing" the tile in
some form of stationery kiln, such as a beehive shaped
brick kiln. The tiles were placed into the kiln and
heated or baked until some transformation of the mineral
particles occurred. This would cause the body to solidify
and, if glazed, for the glaze to melt and fuse to the
body of the tile. The process could take 24 hours or
more for this single firing.
In the pre-World War II era, much of the tile was made
in this batch fashion. The tile body material was fed
into a press usually by hand, then dried, glazed and
baked in a batch kiln. Loading and unloading kilns was
a major labor-consuming item. Finishing was laborious
as well and could involve hand painting tiles, silk
screening, inserting different colored glazes and other
forms of decoration. If a multi-colored tile was to
be produced multiple firings would be required. Thus
the tile would have to be hand-loaded in and out of
the kiln and heated for many cycles before it was completed.
This could take many days for completion of a production
run. The amount of labor was very high.
The firing temperature in these batch kilns could vary
quite a lot from one area of the kiln to another resulting
in size and color variations as well as a high scrap
rate. Thus the yield of a given run could be quite low.
One major improvement from these early method was the
development of the tunnel kiln, a long structure that
had moving transport devices conveying tile through
continuously. The tiles ready for firing were loaded
onto carts with support devices called "kiln furniture"
and the carts pushed through the kiln by some means
including human-power. It took a strong back to push
kiln carts through a 200-foot or longer kiln. Other
innovations in the early 1900's included the use of
conveyor belts to transport the tile from the press
to the finishing department and into the kiln and mechanical
presses to take the human muscle out of the process.
But the industry didn't stop there and is still innovating.
In the 1960's early experimenting with a device called
a "roller-hearth" kiln began. The device consisted
of a series of ceramic rollers that were gear-driven
and would transport a single layer of tiles through
the firing zone of a kiln. This method had several advantages.
Each tile was exposed to a very similar firing condition
making the tiles more uniform. Also the firing time
was reduced to less than 45 minutes and finally, the
tiles could be automatically fed into and out of the
kiln.
By the early 1980's roller-hearth kilns were being
installed in the United States. This was a sea change
for our industry. Other innovations from this period
included hydraulic presses that could generate very
high pressure allowing for larger-sized tiles, greater
body uniformity, and more output per stroke of the press.
The output of the earliest production roller-hearth
kilns was about 6-7 million square feet per year. Today
there are large kilns that will make 30 million square
feet per year with the same number of workers. The process
that is used for most tile production today is known
as the pressed-dust method. It involves grinding the
mineral constituents of the tile body in water slurry.
The tile body is made up of a mixture of various mineral
components depending on the desired properties of the
finished tile, such as feldspar, ball-clay, talc, shale,
etc. ground to a various particle sizes.
This slurry, which contains about 50% water is then
spray-dried to a damp powder and stored to season it.
From storage the powder is fed to the large presses,
some exerting up to 7 tons of pressure, where it is
pressed into the shape of the tile body. The next step
is to convey the tiles into a drier to reduce the water
content to about 2% and then to the glazing line (some
tiles are not glazed) where a plethora of devices may
be used to create the desired look. Some devices include
sprayers, silk-screening devices, dry-glaze dispersers,
waterfalls, rollers, texture imprinters etc.
From the glaze line the tiles enter the kiln where
they may be fired once (monocottura) or several times
if required by a specific design, Then the tiles are
transported directly to an inspection area where a visual
and/or electronic inspection of every tile occurs. The
latest technology provides for complete computer testing
for size, shape, flatness, and finish. Tiles are automatically
sorted to a tolerance of ½ millimeter size and
placed into appropriate caliber stacks and then put
into marked cartons. Most of these steps take place
with no human intervention in the latest technology
driven factory.
At the end of the line, a robot places the cartons
of tile on a pallet for movement into the warehouse.
This is not to say that there are no workers in the
plant. With all this high tech equipment the factory
needs a highly trained and capable maintenance department.
Unfortunately most plants have to contend with kiln
fires, broken rollers, and other mishaps. Since the
process is continuous for 24 hours a day 7 days a week,
the crews must be ready at all times. Changeovers are
required for the various colors, sizes of tiles, and
textures. Ceramic engineers and technicians must be
on hand to develop formulations and techniques for the
different designs. The production managers would love
to run all off-white 12X12 inch tiles all the time but
today's educated consumer wants variety.
Interestingly enough, despite all this technology there
are still tile producers making hand-painted and formed
tile that is batch-fired in the old way (except they
are using small electric kilns instead of the old brick
beehives). The Tile Council of North America has about 50
art tile makers using some of the techniques of yesteryear
mentioned above.
What does this mean for the consumer? For one thing
the reduction in labor has made ceramic tile very affordable.
The price has never been lower in the current period.
Tile is available in many sizes, designs, styles, textures,
and colors thus freeing the designer to create a given
look. Modern techniques permit the manufacturer to make
tile that emulates natural products such as marble,
limestone, granite, slate, etc. Tile that matches older
styles is available for the period look. The properties
of tile such as strength, shape, size tolerance, slip-resistance,
color, shading, are much more uniform and predictable.
New equipment can make individual tile that are 2X4
feet or larger.
In short we've come a long way since the days of the
ancients and we are still going forward.
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