Making Ceramic Tiles
At one point or another, most ceramists decide to make their own tiles. Often
they are disappointed with their first attempts, most commonly because of
warpage. The following tips should help you make tiles that do not warp.
Clay Bodies
The first thing is to start with a good clay body for tiles. Generally this
means tiles that have a high amount of grog. Clays designated for sculpture and
Raku are usually good clays for making tiles. Some people swear by clay bodies
that have a mixture of large and small sized grog.
For durability and waterproofness, you want a clay body that matures at the
temperature you will glaze fire at. This is especially critical for tiles which
are outside or in bathrooms. The absorption rate after firing should be 3% or
less, otherwise water will seep in and cause the tiles to crack. If
waterproofness is not a requirement, you can sometimes achieve flatness easier
by under firing the clay. This is something to experiment with, as other times
a tile that is warped after bisque firing will become flat after glaze firing
if the clay is allowed to mature.
Low fire, smooth, earthenware clay is generally the worst to use for tiles. Not
only does it not fully vitrify, it's lack of grog can be very challenging. An
example of earthenware tiles are Saltillo tiles from Mexico. Since these are
low fired (unvitrified) and unglazed they become easily soiled and must be
sealed several times a year.
Working with the Clay
Once you have chosen a clay, it is best to work with it rather dry. This
reduces warpage problems.
Make sure your tiles are thick enough. If tiles are too thin, they will tend to
warp. An 8 square tile should be at least one half inch thick. This is
thicker than commercial tiles you buy, but those are made with a special dry
pressing process that allows them to be thinner.
It is important not to bend your slabs while they are wet. If you do, the clay
will have a tendency to warp once it is dry. So find a way to handle the slab
without bending them. How? For starters, if you have rolled the slab onto
fabric, do not peel the slab off the fabric. Instead, put a hard board
(plywood, drywall, etc.) on top of the slab, flip the whole thing, then peel
the fabric off the clay. Or simply slide the slab onto a drying board without
bending it.
Alternatively, you can roll the slabs directly onto a board and keep them
there, flat, until they can be slid off. This works with slab rollers like the
Brent where the clay stays stationary and the roller moves across it.
To prevent warpage, some people roll out the slab, flip it over, and roll it
again. Especially if using a slab roller that has a single roller. Since the
North Star type has two rollers that the slab runs through, it is thought to
compress the clay equally on both sides so this step isn't needed.
You can use various materials over your canvas to eliminate the canvas texture
on the tile, as well as keep your canvas from becoming wet and the clay
sticking. Heavy Pellon is sometimes used. It is an interfacing material found
in fabric stores that doesn't stretch or bunch up. Vinyl flooring, and old
lithographic printer's mats are also used for rolling slabs onto.
Alternatives to Rolling
Some people wheel throw their tiles. Just figure the diameter you need to reach
corner to corner on your finished tile including shrinkage, mark that size with
a magic marker on your bat, and throw to the mark. Weigh out the clay balls so
the tiles are always the same thickness when thrown to the mark.
Some people press their tiles. You can make a bottomless frame out of wood,
pound the clay into this form, use your cut off wire to cut off excess clay,
then push the clay out the bottom. To avoid bending, use a piece of wood the
size of the clay to push it through. You will have to let the clay dry to the
point where it doesn't stick to the wood, or use something like WD40 or cooking
oil to coat the wood.
Some people cut their tiles directly off the block of pugged clay. You can buy
devices that act like cheese slicers to cut the clay off at a certain
thickness. Or, to make your own, take two wood dowels (or wood strips) and make
notches at even intervals (one half inch apart for half inch thick tiles.) Wrap
a piece of wire between and around the wood dowels, starting at the top notch.
Grab onto one piece of wood with each hand, pull the wire tight, and sliding
the wood pieces toward, pull the wire evenly through the clay. Make sure you
hold the wood pieces vertical as you pull. Then move the wire to the next lower
notch and repeat.
Cutting the Tiles
Wait until the clay is leather hard before cutting the actual tiles out. Also,
if you are impressing designs make sure you do this before cutting the tiles
out, or the pressing action will deform the shape.
Make a template from metal or wood to make it easy to cut out same size tiles.
Drying
Drying is very critical. You want to make sure the tiles dry evenly on both
sides, or they will warp. Keep them away from drafts, and dry them slowly by
covering with plastic. There are two main techniques used to dry tiles.
1. Place each tile between two pieces of drywall (also called sheetrock.) This
is the stuff used to build walls. You can sandwich many tiles between layers of
sheetrock and stack them up. The moisture is pulled evenly out of both sides. A
variation on this is to dry between layers of three quarter inch thick plywood,
or layers of calcium silicate board (often used as a non-asbestos fire proofing
board).
2. Place the tiles on a wire rack to dry. This allows good air circulation. A
variation on this is drying on plastic grids that are often used in fluorescent
light fixtures.
Other tips are:
7 Use drywall method for the first day or two, then transfer to wire racks.
7 Wax the edges before they dry. This prevents them from drying much faster
than the center. Or wrap dry-cleaning plastic over the edges.
7 Weight the corners with kiln posts overnight -- each stilt laid across the
adjacent corners of two tiles.
Grooves
For functional tiles, people often cut grooves in the back of the tiles. This
allows more surface area for adhesion; they dig into the mortar bed better. An
interesting way to get the grooves is to roll the tiles out onto corrugated,
grooved cardboard. Grooves do not seem to affect warpage.
Firing
For bisque firing, you can stack tiles on top of each other, or put them into a
tile setter.
For glaze firing at low temperatures, tiles can be put into many types of tile
setters. But if you are using high fire clay and firing it to maturity, the
tiles will slump at high temperatures. In these cases you have to fire the
tiles on a flat surface.
Fire tiles on a kiln shelf dusted with silica sand.
Make a moat around your tiles by putting bars of clay around their edges. This
helps them heat from above and below rather than the edges heating faster.
Remember that clay will shrink, and you have to adjust for this when making
your tiles. To determine shrinkage, take a slab of clay and incise a line 100
millimeters long. Re-measure this line at the bisque and high fire state. If
the line ends up 90 mm's long then your shrinkage rate is 10%. If your ending
number is 87mm's then your shrinkage rate is 13%, etc. Remember to make the
first line at the same dryness stage as you will be cutting your tiles, as
there will be shrinkage between wet and leather hard as well.
International Potters' Path
Finally I would like to tell you about a very interesting tile project called
The International Potters' Path. Located at the Chapel of Art, in the shadow of
a 13th century Castle in the UK, this pathway will eventually be 50 square
meters completely paved with 5000 tiles. What is unusual about these tiles is
that they are all being made and donated by ceramic artists, potters and tile
makers from around the world. You can donate a tile yourself! Details can be
found at The
Chapel of Art web site including specifications and some great examples of
tiles already received. Tiles should reflect you, your environment, your
country or culture, and include the name of your town/province or country on
it.