Porcelain vs. Ceramic Tile Is There a difference?

One of the things we are frequently asked about while helping cli­ents select flooring and countertop materials for kitchens and baths is the difference between por­ce­lain and ceramic tile.

People have a sense that ceramic and por­ce­lain tiles are different, and that por­ce­lain tile is somehow the better of the two but they're not sure how they are different or why por­ce­lain is better. ^[1]

The confusion is intentional. If you carefully examine the source of all the myths surrounding por­ce­lain tile, you will find that almost all originate with tile sellers.

Companies that sell tile want you to believe that you really must have por­ce­lain tile in your home because it is so much better than ordinary ceramic.

But, the real motive is monetary. Porcelain tile is usually the more expensive tile and if they can persuade you that you can't possible get along with the less expensive ceramic tile, they make more money.

We don't sell tile. We are tile buyers. We use tile, but we don't make it and we don't sell it.

Several years ago we started wondering what additional features we were buying for the extra money we were spending on por­ce­lain tile. What we found out surprised us, and will very likely surprise you.

So, exactly what is por­ce­lain tile, and is it really better than ceramic tile? Let's see if we can de-mystify por­ce­lain tile a little.

Let's start with this simple, basic fact:

Porcelain and Ceramic Are Not Different Kinds of Tile – They Are Both Ceramic Tile

Bet your tile seller did not tell you that little fact. But, it's absolutely true.

Ceramic is a word derived from the ancient Greek "keramos" meaning roughly "of fired clay". Porcelain is just one of many varieties of ceramic made by firing clay in a kiln.

Ceramic technology is very old. It pre-dates modern humans. The oldest ceramic object discovered so far is a statue called the Venus of Dolni Vestonice, made by a Cro-Magnon artisan some 26,000 years ago in what is now the Czech Republic.

The recipe has not changed over the millennia. All ceramic, including por­ce­lain, is still made out of clay, some additives such as feldspar, bentonite, and quartz; and water.

But, not just any old backyard clay will do. China clay, suitable for making ceramic tile, contains a high proportion of a mineral called kao­li­nite, and, for that reason is often called kao­lin clay or just kao­lin.

The European Definition of Porcelain

Kao­lin results from the chemical decay of silica minerals, mostly feldspar.

Pure kaol­i­nite is bright white but oure kaol­i­note is very rare. Most deposits of tile clay are mixes of kaol­i­nite and other minerals such as alumina, silica, mica, quartz, and, especially, iron oxide.

Iron, which is plentiful in the earth's crust, is the main source of the orange, brown, and terra-cotta colors of most china clays.

The term "por­ce­lain" has been used in Italy at least since at least the late 13th century ^[2] to describe ceramic tile made of white clay.

To medieval Italians, or so the story goes, the resulting ceramic products had the color and luster of the much-admired shell of the porcellana cowrie. So, that's what they called it: porcellana. ^[3] The French corrupted the word to "por­ce­lain" and we adopted (the French say "purloined") the French word.

The clay and additives are mixed with water to produce a paste (or slip) which is formed into a biscuit (or bisque) — the body of the tile — and heated to a very high temperature (usually between 2,000° and 2,500° Fahrenheit) in a kiln using a process first discovered by early humans about 10,000 years ago.

All clay tile is fired the same way. Folk wisdom has it that por­ce­lain tile is better because it contains a higher proportion of kaol­i­nite than red or terra-cotta tile.

But, in fact, it's not the proportion of kaol­i­nite in the mix ^[4] that makes a better tile but the proportion that is chemically trans­formed by firing the tile.

Firing drives out water, hardens the clay and fuses the clay particles together – a process known as sintering. ^[5]

It also changes the silica in the mix to a crude glass which flows into the gaps between the clay particles, sealing them up. This process is known as vitrification. ^[6]

If all of the gaps in the tile are filled with glass, the tile is considered highly vitrified and becomes essentially waterproof.

How much of the mix is vitrified depends on how long and how hot the bisque is fired. If fired for a long time at a high temperature more water is driven out and more sintering and vitrification occurs resulting in a denser, harder tile more resistant to water absorption.

Light-colored clays can be hard-fired, as can more common red, brown, or terra-cotta clays. The firing process is color-blind. The color of the clay makes absolutely no difference.

So, our first definition of por­ce­lain — the traditional or European definition — is simply

A tile made from white or light-colored clay.

That's it. There is no difference between por­ce­lain and other types of ceramic tile in the European tradition other than the color of the bisque.

The tile may be hard, or not; fired for a long time, or not, and very fused and highly vitrified, or not. As used in this traditional sense, the term por­ce­lain tells us nothing about the quality of the tile. It tells us only that the tile is made out of light-colored, porcellana clay rather than red or brown terra-cotta clay.

So, if it's that easy, why is there so much confusion about por­ce­lain tile?

Very briefly, here's what happened: Columbus discovered the Americas; Washington, Franklin, and Adams engineered independence from King George III of England; Americans began making their own ceramic tile and in the process thoroughly muddled the definition of por­ce­lain.

The American Definition of Porcelain

The American definition of por­ce­lain is much newer and very different — almost the exact opposite. It results from the particular American experience with fired clay products.

In the U.S. there are three separate and distinct ceramics in­dus­tries:^[7] ceramic tile, dishware & pottery, and sanitaryware.

There is almost no overlap. Makers of fine china do not produce toilets, toilet manufacturers do not make floor tile and floor tile companies do not manufacture vases or those cute little figurines for your curio cabinet.

This is a little curious because they all use basically the same raw materials and roughly the same manufacturing process: a clay paste is shaped into a product — a salad bowl, sink, vase, floor tile, etc. — and then fired at high temperature to harden the clay. Then the product is covered with an impenetrable, baked-on, glass coating.

In the early days, American tile companies rarely made traditional por­ce­lain tile. If someone wanted por­ce­lain, it was imported from Europe.

But, the other clay industries adopted traditional Euro­pean por­ce­lain very quickly, and their products soon earned a reputation for being of exceptional quality.

By 1917 Len­ox had replaced Euro­pean manufacturers such as Spode and Wedg­wood as the purveyor of fine china to the White House. Koh­ler and Amer­ican Stand­ard had firmly established the "Amer­ican stand­ard" for nearly faultless por­ce­lain bathroom fixtures as early as the 1890s.

By the time American tile makers needed a word to describe their better quality ceramic tile, "por­ce­lain" was available and already well-established in the minds of the buying public as describing ceramic products of exceptional quality.

So, they borrowed it, and por­ce­lain, over time, became the term reserved for better quality tile.

There is some evidence that American por­ce­lain tile followed the Euro­pean practice of using only light-colored clay for a few years. But, after a while, this limitation began to give way so that by the 1970s the term was applied to any high-quality tile no matter the color of the clay.

Today, American por­ce­lain may have a tile body that is red, tan, white, brown — any color so long as the tile is of good quality tile. And that's our second definition of por­ce­lain:

Tile that is considered by its manufacturer to be a superior product.

So, for American tile makers, the defining characteristic of por­ce­lain tile is the quality of the tile, not its color. The tile may be of any color — red, white, buff, gray, terra-cotta, black, blue, or indigo — but it must be a tile of good quality.

Full-Bodied & Through-Bodied Tile

The problem with the American definition is that it conflicts with the general public perception of por­ce­lain.

While most people don't know very much about por­ce­lain, they are pretty sure that it is supposed to be a white- or light-bodied tile, not red, brown, or terracotta.

Con­se­quent­ly, tile sellers often meet with a lot of skepticism when they try to sell red-brown clay tiles as por­ce­lain.

To overcome this problem, American tile manufacturers have come up with a clever distinction between red or brown and light-bodied por­ce­lain tile. Light-bodied tile is "full-bodied" or "through-bodied" por­ce­lain.

So, the salesman can tell you, with an absolutely straight face, that the wine red ceramic tile you are looking at is actually por­ce­lain, it's just not full-bodied por­ce­lain — implying that you must be an unwashed country bumpkin for not knowing the difference.

Irreconcilable Differences

So, we now have two almost opposite and conflicting definitions of por­ce­lain:

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

• The American definition that refers to any high-quality tile as por­ce­lain, irrespective of the color of the tile body.

So, if the tile store clerk claims that the tile you are looking at is "por­ce­lain", what does he mean? Is it a high-quality tile, or a light-bodied tile? Both?

When you buy a tile labeled "por­ce­lain", just what are you buying?

Testing & Rating Ceramic Tile

Although some tile "experts" expound at length on the "special" and "unique" properties of the clay mix used to make por­ce­lain tile, there is, in fact, no such special clay mix (See Some Silly Porcelain Myths).

There are no composition standards at all for general-use clay tile.

No one cares about the type or color of the clay used or just how much or how little kaol­i­nite, or feldspar, or quartz sand, etc. is included in the mixture.

Manufacturers can make tile out of any composition and color of clay, and include any additive that they think will produce a better tile. The standards don't care one way or another.

Nor is anyone particularly concerned about how the tile is made. There are no process standards for general-use tile.

Any manufacturing method that will work is just fine. The tile can be shaped by machine, or by hand. It can be extruded, pressed, or globbed into a form. The tile can be fired using an old tunnel kiln, or the newer roller-kilns, or a kiln at the local high school.

With rare exception — for special purpose tiles — the heat-shield tiles on the space shuttle, for example, the standards simply don't give a hoot how a tile is made.

What the standards do care about and do test extensively is how well the tile performs.

Standards used to rate fired clay tiles are all performance standards.

If a tile performs to a certain standard, it gets rated for that standard no matter what it is made of, how it was made, or what color it is.

Ceramic Tile Performance Standards

Ceramic tile is subjected to a great many tests. It is tested for slipperiness; resistance to cold, heat, and chemical damage; breaking strength, and stain resistance, among others — and we will touch on a few more of these tests in Part 2 of this article.

But, the two most widely used — and certainly the most widely quoted and misquoted — tests of fired clay tile are the wear resistance and water absorption tests.

The wear resistance test, developed by the Porcelain Enamel Institute (PEI) reveals how well the tile resists damage from foot traffic. The absorption test, supervised by the American National Standards Institute (ANSI), looks at how waterproof a tile is.

These distinctions do not necessarily make one tile better or worse than another, they merely help 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 not at all.

A tile that is not very hard may not work for floors or countertops but will be just fine for walls, backsplashes, and hobby crafts where surface wear is not an issue.

PEI Rating: Resistance to Surface Wear

The rating developed by The Porcelain Enamel Institute is a test of surface wear resistance. It involves applying steel ball bearings and aluminum oxide (the grit used in sandpaper) to a tile. A tile is scored by how quickly it shows visible signs of wear.

The classification is colloquially known as the PEI Scale or "Wear Scale". The 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.

(View the PEI Wear Resistance Ratings.)

ANSI Rating: Resistance to Water Penetration

The rating developed by The American National Standards Institute (ANSI) is a test of resistance to permeability by water. It consists of weighing the tile, then boiling it for five hours. The tile is then soaked in cold water for another 24 hours. It is then measured again to find its gain in weight from the original dry state.

Any weight gain indicates water absorbed by the tile. The result is stated as a percent of change from its original dry weight. ^[8] Four ratings resulted from ANSI's studies of clay-fired tiles. These are, from lowest to highest: Non-Vitreous, Semi-Vitreous, Vitreous and Impervious.

Non-vitreous tile is the most permeable. Semi-vitreous is slightly less so because more of the tiny spaces between clay particles have been filled with glass. A Vitreous tile is even less permeable.

An Impervious tile is the least porous — in fact, it is essentially waterproof — but instead of calling it super-vitreous or waterproof, the creators of the test settled on Impervious.

Waterproof would actually be the more accurate term. Impervious (in regular English as opposed to engineer-speak) means more than just waterproof. It also means "impregnable" or "invulnerable".

Impervious tile is neither impregnable nor invulnerable.

Hit it with a hammer, it will break. So, when you see or hear the word impervious applied to tile, think "waterproof". That way your mind won't be fooled into thinking the tile is something it's not.

(View the ANSI Water Re­sis­tance Ratings.)

The ANSI-PEI Relationshiip

There is a relation between the two ratings, at least for unglazed tiles such as quarry or saltillo tiles.

Tile that is harder and thus more wear-resistant is a tile that was fired longer or at a higher temperature or both. This is also the tile that tends to be more resistant to water penetration.

With glazed tiles, however, the relationship breaks down. If a tile has a surface glaze, the glaze becomes the wear layer, and it is the glaze that is subjected to the PEI wear test, not the body of the tile beneath the glaze.

A very hard glaze can be applied to a very soft tile, so, with glazed tiles, it is possible to achieve a high wear rating with a low water-resistance score. (More about tile glaze below.)

The ANSI Definition of Porcelain Tile

We already have two different definitions of por­ce­lain tile: the traditional or Euro­pean definition, and the newer American definition. And, just to make things even more fun, there is yet a third generally accepted definition: the ANSI definition of por­ce­lain.

In 1988, under pressure from American tile manufacturers and seeking to clarify once and for all time the burning international issue of what is a por­ce­lain tile, the American National Standards Institute (ANSI – the same guys that developed the water-resistance test) adopted what it hoped would become the only official U.S. definition of por­ce­lain tile, assigning, they hoped, the traditional color-based definition to oblivion.

In its American National Standard Specifications for Ceramic Tile (ANSI A137.1) ANSI declared a tile to be por­ce­lain only 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 a 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 (See above). The second is something rarer — a "process" test. To be called por­ce­lain, tile must be made by the "dust press" method or process.

The dust or "dry" press method is a process for manufacturing tile that has very little to do with tile quality. It is mostly a measure for controlling tile shrinkage.

All fired clay tile shrinks when it is fired and water in the biscuit evaporates. If there is a lot of water, there is a lot of evaporation and, consequently, a lot of shrinkage. Controlling shrinkage is important if the resulting tiles are to be the same finished size, or "caliber".

Caliber is important. If tiles vary too much in face dimensions they are much harder to set in a pleasing, un­iform manner and often require a wide grout line to mask the unevenness of the tile. Tiles that are very similar in finished size can be set with a narrower grout line.

The dust press method does not actually use dust to make a bisque. A little water — about 6% — is required to dampen the clay mix which is then pressed into shape. The pressure helps the clay particles stick together so the bisque retains its shape. With so little water in the mix, 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, as we know, pro­cess standards are very rare in the tile world, and almost unheard of when rating general use tile. Accordingly, this one did not last long.

Since the standard was first issued, tile chemists and materials engineers have made enormous strides in controlling shrinkage using the extrusion process — primarily through additives, such as calcium lignosulfonate, that make water "wetter". ^[9]

Wetter water means less water is needed in the paste. As a result, extrusion now produces tile of very uniform caliber.

Recognizing this change, ANSI dropped the requirement that por­ce­lain be made by the dust press process in its later versions of A137.1. Any manufacturing process may now be used to make por­ce­lain tile as long as the tile rates Impervious.

The effect is that "por­ce­lain" under the ANSI standard has become just an alternate word for "Impervious", which, as we noted earlier, is just engineer-speak for "waterproof". If a tile meets the criteria for being rated Impervious to water penetration, it may, according to ANSI, be called por­ce­lain.

American tile manufacturers welcomed the new standard with warm applause and great enthusiasm. Euro­pean, South American, and most Asian tile makers greeted it with a great big yawn and cheerfully ignored it.

Imported tile is generally rated under a different set of standards published by the International Standards Organization (ISO), which had until recently, very wisely, stayed far away from the fray over what is or is not por­ce­lain tile

Consequently, imported tiles were free to adhere to the Euro­pean definition that declared tile to be por­ce­lain if made with light-colored clay.

The ISO Definition of Porcelain Tile

But, not having an "official" definition of por­ce­lain caused problems for the ISO.

The U.S. market for ceramic tile is massive — about equal to the entire continent of Europe, so most foreign tile manufacturers want to export to the U.S. But, in order to get an "official" por­ce­lain designation for their qualifying tile, they needed to be certified by ANSI.

This started costing ISO customers as more manufactures switched to ANSI for tile certification.

In 2012 the ISO caved in. The standard that defines and classifies ceramic tile (ISO 13006) was revised to define por­ce­lain tile as tile that is

fully vitrified tile with water absorption coefficient less than or equal to a mass fraction of 0.5%…

which is essentially the ANSI definition — a tile may be called por­ce­lain if it absorbs less than .05% water by volume, or is, in other words, rated Impervious in the ANSI water absorption test.

(Actually, the ISO has its own slightly different, somewhat less stringent test — why let the ANSI guys have all the glory, right?)

So, it was a long road but everyone finally agrees that the old color-based definition of por­ce­lain is extinct. The term por­ce­lain will be reserved only for high-quality tile in the American tradition that meets either the ANSI or ISO standard for Impervious tile. Right?

Not a chance! Sorry! Wish it were that easy.

If some law required ceramic tile to be graded, then a standard defining por­ce­lain would eliminate any issue about what is or is not por­ce­lain tile. The question would then be which of the competing standards to use.

But, both ANSI and ISO standards are completely voluntary.

No tile maker is bound to observe them. And, a great many don't. Ceramic tile may legitimately be called por­ce­lain even if it is not "Impervious" as long as it does not claim to meet the ANSI (or ISO) standard for por­ce­lain.

So, where does that leave us?

Unfortunately, just about where we started. The attempt by the standards organizations to create a universal standard for por­ce­lain has really had little effect except to make a confusing situation even more confusing.

Both the ANSI and ISO standards are less than 50 years old in an industry that was already many thousands of years old before Rome was an Empire.

Many tile makers choose to ignore these new standards, especially traditionalist manufacturers that still adhere to the older color-based, definition of por­celain tile.

And, while American tile manufacturers have tried mightily to get the ANSI definition enacted into federal law, our Right Honorable Congress-Persons have so far been busy with much weightier matters — primarily getting re-elected and calling each other names. ^[10]

As the situation now stands, the use of the word por­ce­lain to describe ceramic tile has been left almost entirely to the discretion of individual tile manufacturers. Whe­ther they have their tiles tested and certified under either ANSI or the ISO standard as por­ce­lain, and how and when they use the term to describe their tile is completely up to them.

As a result, when the word por­ce­lain appears on a box of tile it is often not possible to discover what it actually means. It may legitimately mean …

So, does the word "por­ce­lain" printed on the box actually help you select a suitable tile?

It tells you nothing about the color of the tile — por­ce­lain in the American tradition can be of any color.

It does not reveal anything about the quality of the tile — por­ce­lain in the Euro­pean tradition may be of any quality.

In fact, it does not tell you much of anything useful about the tile. The term "por­ce­lain" is so ambiguous as to be useless. If the tile meets any of the many definitions of por­ce­lain, and its manufacturer elects to call it por­ce­lain, then it is — legitimately — por­ce­lain.

Our best advice: ignore the term por­ce­lain altogether when shopping for clay-fired tiles. Disregarding the dubious distinction between por­ce­lain and other ceramic tile actually makes choosing tile much, much easier and a lot less confusing.

To find out how to actually buy the right ceramic tile for your project, Continue to the next section: How to Choose Ceramic Tile.

Footnotes

Rev. 05/31/21