Intro
| The Tile-Making Process | Historical
Background | Ceramic Floor Tile Types | Laying
Ceramic Tile Floors | Historic Ceramic Floor Tile: Preservation and
Maintenance | Historic Ceramic Floor Tile: Damage and Deterioration
Problems | Historic Ceramic Floor Tile: Repair and Replacement | Summary | Some Sources for Replacement Tiles
Ceramic floor tiles can
generally be divided into two types: unglazed and glazed. Unglazed tiles
include: quarry tiles; encaustic and geometric tiles; and ceramic mosaic tiles, which can
be either glazed or unglazed. Most other ceramic floor tiles are glazed.
The thickness of historic ceramic floor tiles varied considerably according to
their intended use and when they were made. Floor tiles were thicker and harder than wall
or ceiling tiles.
Stove tiles, meant to retain the heat of the stove, were sometimes as much as several
inches thick. Medieval floor tiles were usually one inch thick; encaustic tiles of the
Victorian era tended to be slightly thinner.
Modern, 20th-century tiles, with the exception of some art pottery tiles, are the
thinnest, as a result of modern manufacturing methods. The backs of most, but not all,
ceramic floor tiles are covered with raised (or sometimes recessed) ridges, circles or
squares which help to increase the bonding capability of the tile.
Unglazed Tiles
Quarry tiles are the most basic type of historic ceramic floor tile. Originally
made from quarried stone, they are machine-made using the extrusion process. Quarry tiles
are unglazed, semi-vitreous or vitreous, and essentially are square or rectangular slabs
of clay baked in a kiln. The colors of quarry tiles are natural earthen shades of gray,
red and brown determined by the clay and, to some extent, the temperature and duration of
firing. Quarry tiles, which range from ¼" to ½" in thickness, are available in
square and rectangular shapes in sizes that include 3", 4-1/4", 6" (one of
the most common sizes), 9" and 12" squares; 6" x 12", 6" x
9", 4-1/4" x 9", 3" x 6", and 3" x 9" rectangles; and
4" x 8" hexagon shapes. (Pavers or paver tiles are a simpler, and tend to be
somewhat cruder, version of quarry tiles. Like quarry tiles, they are usually unglazed,
but slightly thicker. Machine-made pavers are either semi-vitreous or vitreous, and
generally formed by dust-pressing, although sometimes are extruded. Hand-made pavers which
are common in Mexico and southern Europe are non-vitreous.)
Encaustic tiles are a type of traditional unglazed-yet decorative-floor tile,
manufactured by the dust-pressed method. Whereas most ceramic tiles are surface-decorated
or decorated with impressed or embossed designs created by a mold, encaustic tiles are
unique in that their decorative designs are not on the surface, but are inlaid patterns
created as part of the manufacturing process.
First, a thin, approximately ¼" layer of fine, almost powder-dry, clay was
pressed into a mold with a relief design at the bottom which formed a depression in the
face of the tile. A second, thicker layer of coarser clay was laid over the first layer,
then covered with another layer of fine clay. This "sandwich" helped prevent
warping and ensured that the body of the tile was strong and had a fine, smooth surface.
The layers of clay "dust" were compacted by presses, after which the mold was
inverted and the die removed, thus producing a tile with an indented or intaglio pattern
on top. After the tile dried, colored slip (liquid white clay colored with dyes), was
poured to fill in the intaglio pattern. Each color had to dry before another color of slip
was added.
The recessed area was overfilled to allow for shrinkage, and after drying for several
days, and before firing, the excess slip was scraped off the surface by a rotating cutter
that created a flat, although not completely smooth, face. Problems might arise during the
firing. Due to the dissimilar rates of contraction of the different clays, the inlaid clay
could shrink too much and fall out of the tile recesses; or, the tile could be stained by
the different pigments used for the design if impure or unstable. By the 1840s, encaustic
tiles were made entirely with almost-dry clay using the dust-pressed method. This served
to eliminate the possibility of staining the body of the tile with other colors and
permitted the use of more colors on a single tile.
Thus, an encaustic tile can sometimes be dated according to the complexity and the
number of colors in its pattern. Red tiles with white figurative patterns were generally
the earliest, followed by brown and buff colored tiles. In the 1860s, blue tiles with
yellow or buff patterns were popular, succeeded by more subtle color schemes featuring a
"chocolate" red with a soft grey. By 1860, up to six colors were used in a
single tile to form a pattern. Toward the end of the century, white encaustic tiles with a
black or gold design were common, as well as tiles with complicated color patterns of
white, black, gold, pink, green and blue.
Encaustic tiles were decorated with traditional as well as original designs. Some,
particularly intricate, designs were painted on the surface of the tile with opaque
colored glazes, instead of being inlaid. Most major tile manufacturers sold many of the
same pre-formed encaustic floor tile patterns through catalogues. Encaustic tiles were
produced in a variety of sizes, mostly square or octagonal in shape, and almost any design
could be custom-made for a special purpose or to fit a particular space.
Historic, 19th-century encaustic tiles were generally slightly less than 1" thick,
about 15/16." Cheaper tiles of lesser quality were also made of clay or cement. These
designs resembled those commonly found on encaustic tiles but applied as a transfer
printed pattern, or using a multi-color lithographic or silkscreen process. These are
still manufactured and popular in many parts of the world.
Smaller, single-colored versions of encaustic tiles that, when assembled together form
a geometric pattern, are called geometric tiles in England. However, in the United
States they are generally not differentiated from encaustic tiles. Based on the
geometric segments of a six-inch square, they were typically rectangular, square,
triangular or hexagonal in shape, and about the same thickness as patterned encaustic
tiles.
Geometric tiles were especially well suited for decorative borders, and a wide variety
of floor designs could be created with their many shapes, sizes and colors-either alone or
combined with patterned encaustic tiles. The cost of producing geometric tiles was much
less than of encaustic tiles because each tile involved only one type of clay and one
color. By the end of the 19th century, over 60 different shapes and sizes of geometric
tiles were available in up to ten colors, including buff, beige or tan, salmon, light
grey, dark grey, red, chocolate, blue, white and black.
Ceramic mosaic tiles are essentially smaller versions of geometric tiles
(usually no larger than 2-1/4", and no thicker than ¼") ranging in size from
½" to 2 3/16", in square, rectangular or oblong, hexagonal, pentagonal and
trapezoidal shapes. Both vitreous and semi-vitreous mosaic tiles were available, unglazed
in solid or variegated colors with a matte finish, or glazed in unlimited colors. Single,
one-piece tiles were also fabricated to give the appearance of multiple mosaic pieces.
This was achieved with a mold, which gave the appearance of recessed mortar joints
separating individual "mosaics" .
Glazed Tiles
With the exception of quarry tiles, encaustic tiles, and some mosaic tiles, most
ceramic floor tiles are decorated with a glaze.
While unglazed tiles derive their color solely from the clay, or from oxides, dyes or
pigments added to the clay, the color of glazed tiles is provided by the glaze, either
shiny or matte. Some potteries specialized in certain kinds of glazes and were famous for
them. The earliest and most common method of clay tile decoration made use of tin-glazes
which were essentially transparent lead glazes.
Tiles were either dipped into the glaze or the glaze was brushed on the tile surface.
Glazes were generally made with white lead, flint, or china clays ground up and mixed with
finely ground metallic oxides that provided the color. Colored glazes were commonly known
as "enamels".
Colors included blue derived from cobalt, green from copper, purple from manganese,
yellow from antimony and lead, and reds and browns from iron. An opaque glaze was created
by adding tin oxide.
