Porcelain or Ceramic: What Is the Difference?
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Reader Comments:
Thank you so much for a very well done, under­stand­able, common-sense explanation.

J.T., Arlington, VA One of the things we are frequently asked about when helping clients select flooring materials for kitchens and baths is the difference between porcelain and ceramic tile. People have a sense that porcelain tile is somehow better, but they're not sure of exactly why it is better.

That's because, despite all the hype, porcelain tile is not necessarily better than ceramic tile, so there is usually no reason to spent more money on a tile just because it calls itself porcelain.

So, exactly what is porcelain tile? Let's start with a definition of the term "porcelain".

The European Definition of Porcelain
Photo: Trikeenan Tile Works. Tile bathroom An extraordinary tile bath composed of Trikeenam Tile Milk Wite tile on walls and Fog Weave on the bathroom floor. Tile used on the floor of a bath should be rated at least "Vitreous" and PEI Group II (light duty floor). The ratings are printed on the box. Porcelain and ceramic are not different kinds of tile. Porcelain is just one of many varieties of ceramic tile. Ceramic is a word derived from the ancient Greek "keramos" meaning roughly "of fired clay". All ceramic tiles, including porcelain, are made out of clay, some additives (such as feldspar and quartz sand), and water.

But, not just any kind of clay will do. Tile clay contains a high proportion of a mineral called kaolinite or "china clay". This clay results from the chemical decay of silica minerals, mostly feldspar. Pure kaolinite is bright white, but white deposits are very rare. Most natural deposits of kaolinite also contain iron oxide which darkens its color. A little oxide results in yellow, tan, pink or light orange clay. A lot of iron oxide produces the more familiar red or brown terra-cotta clay. Traditionally, the term "porcelain" or "porcelano" has always been used to indicate a ceramic tile made of lighter clays containing only a little iron oxide. The more expensive white clay is used mostly in chinaware and dishes — not tile.

This clay mix is formed into a "biscuit" — the body of the tile — and heated to a very high temperature in a kiln using a process at least 3,000 years old. Folk wisdom has it that porcelain clay makes a better tile because it contains a higher proportion of kaolinite than red or terra-cotta clay. But the plain truth is that it is not so much the proportion of kaolinite in the clay that matters, but the proportion that is crystallized by firing.

Firing drives out water and crystallizes some of the molecules in the clay into a form of low-order glass. This makes the tiles harder and more water-resistant. How much clay is crystallized depends on how long and how hot the clay is fired. If fired for a long time at very high temperature, more water is driven out and more crystallization occurs, resulting in a denser, harder product more resistant to water absorption. Porcelain clays can be hard fired, as can traditional terra-cotta clays. The color of the clay makes no difference to the firing process.

So, our first definition of porcelain — the traditional or European definition — is a tile made from light-colored clay. It tells you nothing about the quality of the tile. The tile may be hard, or not; fired for a long time, or not; and very crystallized, or not. Used in the traditional sense, the term "porcelain" tells us only that the body of the tile was made out of light-colored rather than a red or brown clay.

The American Definition of Porcelain
The traditional American definition of porcelain is very different — almost the exact opposite, in fact.

American tile makers have long reserved the word "porcelain" for only their premium lines of tile. These may have a tile body that is red, tan, white, brown — any color so long as the quality of the tile is very high. Porcelain as the word is used by U. S. manufacturers tells us nothing about the composition of the tile or the color of the clay. It tells us only that its manufacturer considers it to be very good tile.

The problem with this definition is that it conflicts with the general public perception of porcelain. While most people don't know much about porcelain, they do know that it is a light-bodied tile, not red or brown. Consequently, tile sellers often meet with a lot of skepticism when they try to sell red and brown tiles as porcelain. To overcome this problem, American tile manufacturers have come up with a distinction between red porcelain tile and light bodied porcelain. Light-bodied tile is "full bodied" or "through bodied" porcelain. So, the salesman can tell you, with an absolutely straight face, that a deep red tile you are looking at is actually porcelain, it's just not "full-bodied" porcelain — implying that you are an unwashed country hick for not knowing the difference.

White Tile bathroom Tile for use in wet areas like a bath floor should be highly slip resistant. This narrow format tile applied vertically creates a striking setting for a modern urban bath. So, we now have two almost opposite and conflicting definitions of porcelain:

•  The European definition that refers to any light-colored tile as porcelain, no matter the quality of the tile; and

•  The American tradition that refers to any high quality tile as porcelain, no matter the color of the tile body.

Because American porcelain is high-quality tile it is often more expensive than European and Asian porcelain that may be of a much lower quality and therefore cheaper to make. This competitive disadvantage irritates American tile makers to the point that they have long clamored for a standard that excludes lower quality tile from being called porcelain. So far they have not had much luck.

Ceramic Tile Standards
You'd think that as much as the term porcelain is used to describe ceramic tile someone would have long ago come up with a universal standard defining porcelain tile. But no, they haven't. There are no "composition" standards at all for general-use clay tile. No one cares about the type or color of the clay or just how much or how little kaolinite is included. There are no standards that specify the type of additives that may be used. Manufacturers can make tile out of any composition and color of clay, include any additive in the mix that they think will produce a better tile, and (with some rare exception) use any manufacturing process they want. The standards don't care. All the testers care about is how well the tile performs. Standards used to rate fired clay tiles are all "performance" standards.

Tile is subjected to a great many tests, and we will touch on a few more later in this article. But probably the two most important tests of fired clay tile are the hardness and water absorption tests.

The hardness test, developed by the Porcelain Enamel Institute (PEI) tests how resistant a tile is to wear from foot traffic. The absorption test, supervised by the American National Standards Instituted (ANSI), looks at how well a tile resists penetration by water. Relative hardness is important because a hard tile is less likely to wear and less likely to break. Water absorption is also important because the more water-resistant a tile, the more diverse applications it has. These distinctions do not necessarily make one tile better or worse than another, they merely determine where and how a tile may be used. A tile that absorbs a lot of water should not be used outside where it freezes because the freeze-thaw cycle will crack the tile. But it may be quite suitable as wall tile around a fireplace where water absorption matters little. A tile that is not very hard may not be suitable for floors, but may be just fine for walls, table tops, and hobby crafts.

PEI Rating: Resistance to Wear
The rating developed by The Porcelain Enamel Institute, is a test of hardness. This test is approved by the American Society for Testing and Materials (ASTM). The classification resulting from this test is of the relative resistance of a tile to surface damage caused by abrasion and wear.

The classification is known as the PEI Scale. These classifications are numeric. The numbers define the suitable uses for the tile. The higher the number, the more wear-resistant the tile and the more places it can be used.

Class Application
Group IThe softest tile. Suitable for walls only, no floors.
Group IIResidential use in low foot traffic areas. In rooms where there is usually no through traffic, this tile might work. But in kitchens, where there is often a lot of through traffic, this tile would be suspect.
Group IIIAll residential, medium commercial, normal foot traffic (interior only). Any bathroom or kitchen, mudroom, laundry room or hallway, but nothing outside.
Group IV Heavy commercial. Any interior use.
Group IV+ (or V)The hardest tile. Extra heavy commercial (interior or exterior use).

ANSI Rating: Resistance to Water Penetration
The rating developed by The American National Standards Institute (ANSI A137.1) is a test of resistance to permeability by water. It consists of boiling the tile in water and measuring its gain in weight from the original dry state. Four ratings resulted from their studies of clay-fired tiles. These are, from lowest to highest:

Rating Description Application
Non-vitreous Water absorption of more than 7.0% by volume. Tile for non-wet areas. Around fireplaces, for example. Typically intended for walls, hobby and crafts use.
Semi-vitreous Water absorption of more than 3.0 percent, but not more than 7.0 percent. Tile for areas that may get wet on occasion, but are unlikely to see constant or standing water. Kitchen backsplashes, for example.
Vitreous Water absorption of more than 0.5 percent, but not more than 3.0 percent. Virtually any indoor application including shower walls and floors. Outdoors in areas that do not freeze.
Impervious Water absorption of 0.5 percent or less. Any indoor or outdoor application.


The ANSI Definition of Porcelain Tile
We already have two different definitions of porcelain tile: the European definition and the American definition. There is a third definition, however: The ANSI definition.

Under pressure from American tile manufacturers and seeking to clarify the issue of what is a porcelain tile, ANSI in 1988 adopted what it hoped would become the standard definition of porcelain tile in ANSI A137.1 which declared a tile to be porcelain if it is:
"...generally made by the dust-pressed method of a composition resulting in a tile that is dense, impervious, fine-grained, and smooth with sharply formed face."
While this is definitely written in engineer-speak, what it does is define two different tests for identifying a porcelain tile. The first is the same performance test used to rate all tile. A porcelain tile must perform at the highest "impervious" standard in the ANSI water-absorption test. The second is something new — a "process" test. To be called porcelain, tile must be made by the dust press method or process.

The dust or "dry" press method of forming tile has little to do with tile quality. It is a measure for controlling tile shrinkage. All tile shrinks when it is fired and water in the biscuit evaporates. If there is a lot of water, there is a lot of shrinkage. Controlling shrinkage is important if the resulting tiles are to be the same finished size. The dust press method uses very little water in the clay mix, so shrinkage is minimal and the resulting tiles are likely to be of a more uniform size. The other, more widely used method, is the extrusion process in which slightly wetter clay is fed into a mold that extrudes a ribbon of biscuit that is then sliced into individual tiles. In the past, shrinkage was a little less controlled using this method. However, since 1988 tile chemists and engineers have made enormous strides in controlling shrinkage using the extrusion process, so much so that either method now produces very uniform tile. Recognizing this change ANSI dropped the requirement that porcelain be made by the dust press process in its latest version of A137.1. Any manufacturing process can now be used to make porcelain tile as long as the tile rates "impervious". Ceramic and Porcelain Tiles The top row contains ceramic tiles, the bottom row porcelain tiles. Can you tell the difference? We can't.

The effect is that "porcelain" under the ANSI standard has become just an alternate name for "impervious" tile. If a tile meets the criteria for being considered impervious, it is automatically porcelain.

Does this mean that only tile meeting the ANSI standard can be referred to as porcelain? Unfortunately, it does not.

European and most Asian tile makers have studiously ignored the ANSI definition. Imported tile is tested under a different set of standards published by the International Standards Organization (ISO), which has, wisely, stayed out of the fray over porcelain. It has made no attempt to define its own standard for porcelain.

Consequently, imported tile generally adheres to the European tradition — tile is porcelain if it is made with light-colored clay and its manufacturer calls it porcelain.

Not even American manufacturers are bound by the standard. American-made tile may legitimately be called porcelain even if it is not "impervious" as long as it does not claim to meet the ANSI standard for porcelain. You can generally count on American-made "porcelain" to be good quality tile, but how good varies from firm to firm and is determined only by a company's internal standards.

So, this attempt by ANSI to set a standard for the use of the term has really had very little effect except to further muddle the issue. And while many American tile manufacturers have tried mightily to get the ANSI definition enacted into federal law, Congress has so far remained wholly uninterested.

How to Actually Buy Tile
So, If you see the term "porcelain" on a box of tile, just what does it tell you? The answer is: not very much.

It may legitimately mean So does the word "porcelain" actually help you select a suitable tile? No, it does not. The term "porcelain" is ambiguous — you cannot tell exactly what it means when applied to a particular tile. Things may change later, but right now, the term is little more than a an indication of the tile manufacture's opinion about its own tile. If the tile legitimately meets any of the three definitions of porcelain, and its manufacturer elects to call it porcelain, then it is porcelain.
Photo: NET Television. Tile kitchen backsplash
Click to Enlarge
 Tile protects the wall behind a kitchen prep sink and provides a decorative element to enhance the area.


Do we actually care about that? How useful to us is a manufacturer's opinion about its own tile?

Our best advice: ignore the term porcelain altogether when shopping for clay-fired tiles. Pretend the word was never invented, or is a strange word in an obscure foreign language, like Cornish (10 known speakers worldwide). Disregarding the completely useless distinction between porcelain and ceramic tile actually makes choosing tile much easier.

Instead of trying to figure out if a tile is or is not porcelain, just look for the size, pattern, price and color that works best for you in a tile rated for the application you intend. Ignore, for the moment, whether the tile is light-bodied or red. It will only rarely make any difference to the appearance of the installed tile. What does make the difference is the tile's glaze.

The Tile Glaze
Some fired clay tiles, quarry and saltillo tiles, for example, are not glazed. In these tiles the color of the tile body is the color you see, so it makes a difference what clay was used to make the tile. But most ceramic tiles have a coat of opaque, glassy material on the face of the tile that we call the glaze.

There are emerging one-step processes in which the tile and glaze are fired at the same time. But traditionally glaze is applied after the biscuit is fired, then the tile is fired again to set the glaze. It's this glaze that gives the tile its color and texture, not the composition of the tile body. The glaze is the tile's paint.

Think of wood siding. You don't see the wood in your siding. What you see is the coating on the wood — the paint. Most likely you don't even know what kind of wood was used for your siding, or if it was wood at all. It may be Masonite™ or one of the more contemporary products, cementitious siding, for example, which contains no wood at all yet when painted looks exactly like wood siding.

We have heard mentioned from time to time that the glaze on good porcelain tiles is "deeper" than that on ceramic tiles, but that's just another nonsense myth. Glaze is "deep" if the producer applies a thick coat of glaze, it makes no difference what kind of backing material the glaze is applied to. This is yet another of those fables surrounding porcelain tile that just won't go away.

Once tile is installed you don't see the tile body, you see the glaze. So what difference does it make if the tile body is white, sand, terra-cotta or puce? If you need to go around a corner where the edge of the tile will be exposed, there are special edge tiles made just for that purpose. And if you can't find a matching edge tile, your tile setter has a few tricks to disguise the edge.

How to Read a Tile Label
Once you have found the color and pattern of a tile that you like, then all the other information you need to assess the usefulness of the tile is printed somewhere on the box in the form of icons. These icons tell us all about the tile, and since their use is regulated, the information in the icons is probably not going to be just marketing hype. Let's see just what these icons can tell us.

Grade Icon This grade is the result of a visual inspection. The range is 1 to 3, the lower the number the better the tile. A grade 1 or Standard Grade tile exhibits no obvious imperfections when visually inspected at a distance of 3 feet. A grade 2 tile shows no visible imperfections at a distance of 10 feet. Almost all tile in a tile store will be grade 1. Sometimes you will find grade 2 tile on a "special purchase" sale — often at quite the discount. Grade 2 is just fine for many applications. The durability of a grade 2 tile is usually not suspect, it merely has visible imperfections. We sometimes use it in historical renovations to simulate 19th century tile that often had many visible flaws. Grade 3 tile is rarely seen in retail stores. It usually has major aesthetic problems including wide variations in tone and sizing. Let the tile professionals buy this tile. They know where and how to use it.
PEI Icon This is the result of the PEI wear test that we introduced earlier (See chart above). Many manufacturers use this test only on floor tiles. The higher the rating, the more wear-resistant the tile. A tile used as flooring or on a countertop should be rated at least in Group III. A higher rating is even better for floors. It should also be between 3/16" and 1/4" thick. Thicker is generally better. If this rating is missing, the tile is probably not intended for floors.
WA Icon This is the score the tile received on the ANSI test for resistance to water penetration (See chart above). A tile that is installed outdoors where there is a real Winter should be rated impervious to water penetration. Otherwise, water trapped within the tile may freeze, fracturing and cracking the tile. For indoor applications, semi-vitreous and vitreous are strong enough for floors, and non-vitreous for walls. In some locations where the freeze is neither hard nor long, semi-vitreous tiles can be used outdoors — not recommended in Nebraska, however.
COF Icon For floor tile, this Coefficient of Friction (C.O.F) ranking is important. The test establishes how much force is required to move an object across the face of the tile, dry or wet. It tells you how resistant a tile is to slipping. The higher the score, the more slip-resistant the tile. Tile COF can be rated "wet" or "dry". For a general floor, look for a dry rating of 0.5 and above. For a bath or kitchen, where the floor is likely to get wet, a wet rating of 0.5 or greater is required and 0.7 or higher is better. Some tiles specifically designed for wet floors are rated above 0.85. COF is an important consideration, especially in wet areas. One of my neighbors ignored COF when selecting impervious tile for his front stoop, and now, on wet days, you have to tip-toe over the tile with a death-grip on the handrail to avoid major injury.

There are problems with this test, however. The testing process involves pulling a weighted board with a Neolite (rubber) sole (used to simulate the bottom of a shoe) along the surface of a test tile. This is called a static slip test. However, the way we walk involves more than just slip-sliding along. There is both downward and outward force applied with each step we take. The standard slip test tells us nothing about the effects of these forces.

To test downward and outward force, what's needed is a dynamic test. There are a number of dynamic resistance tests, but none has yet been approved for testing tile in the U.S. The most widely accepted test in Europe is the ramp test (DIN 51130). The test involves a person walking along a platform of tiles that are being tested. The incline is then increased to a point where the person starts to slip. Obviously, since people react differently when anticipating a slip — including changing their stride and walking more carefully — and some acrobatic individuals walk just fine on slippery slopes that would kill the rest of us, this test has some basic reliability problems. It has not been adopted outside of Europe.
FROST Icon If present, the "Frost" icon merely tells you that the tile can be used where it might freeze — in other words, it is an impervious or at minimum a vitreous tile. Look at the W.A. test to find out which. In Nebraska, don't rely on the Frost icon. Look for impervious tile for use outdoors. If there is no frost icon, the tile cannot be used outdoors in any place where it might freeze.
TONE Icon The tone rating is an indication of how much variation there is in the color and pattern of the tile. If there is a lot of variation in the tone grid, examine more than one tile, and more than one box of tiles to see if you like all the various tones. Tone variation is very common. Only pure color tiles such as pure whites and blacks have almost none. Perhaps more important than tone variation is size variation. Check to see that there is very little variation in the size of the tiles in a box. Tile made in the U.S. has very little variation, but tile made elsewhere may not be as precise.

Some Informal Quality Tests
How did we tell good tile from bad before there were these helpful package ratings? There are traditional tests that can be used to help judge the quality of a tile. Here are some rule-of-thumb tests that have been around for many years.

The Weight Test: Hard fired tile is generally denser and therefore heavier that softer tile. You probably can't judge comparing single tiles, but heft the boxes. The heavier box is usually the harder tile.

The Ring Test: Hold a tile between thumb a forefinger at one corner and let it dangle. Snap near the opposite corner with your fingernail. A tile with a high crystallization content will ring like a lead crystal glass. The sharper and higher the ring, the better the tile. If it goes "thunk", think of it as wall tile.

The Color Test: Hard fired terra-cotta tile is generally browner. We don't know why. It may be the composition of the clay or the fact that high firing turns the clay browner. And it's not always true. But generally hard fired tile is browner.

The Slip and Fall Test: The C.O.F. rating indirectly tells you whether a tile is slippery, but the direct test is still probably the best test. Put the tile on the floor and walk on it. If you slip and fall, don't buy the tile, and call a lawyer. If you need a wet slip test, toss some water on it first. The tile store clerk will probably go batty when you do this, but if you want to be completely satisfied that a tile is not slippery, do it anyway. We do.

Don't, by the way, rely exclusively on any of these rule-of-thumb tests. Read the ratings on the box. But you can use these to impress the salesman with your "in-depth" knowledge of fired clay tile.

The Three Tile-Buying Do's and Don'ts
So, at the end of all this discussion we end up with just three simple rules for buying tile.
So, is it Porcelain or is it Ceramic?
Who cares? As we have seen, a tile deemed "porcelain" by its manufacturer is not necessarily better, harder, more durable, more scratch resistant or even always more expensive than a ceramic tile; and if you paid more for a tile because it said "porcelain" on the box, you've just been had by a marketing trick that dates back beyond the ancient Greeks to the even more ancient Chinese.

The only two things that actually matter are whether you like the look of the tile and whether it is rated for how you intend to use it. A tile rated for the application you have in mind will work whether the manufacturer chooses to call it porcelain or not.

So, if the tile salesman tries to "upgrade" you to a more expensive "porcelain" tile, look bored and yawn a lot. You know that there is no practical difference between ceramic and porcelain tiles. Aw, what the hell, "accidently" drop a box of tile on his toes for trying to trick you — scoundrel that he is.