Porcelain or Ceramic Tile: What Is the Difference?

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.

So, exactly what is porcelain tile, and is it better than ceramic tile?

The European Definition of Porcelain
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 backyard clay will do. Tile clay or "china clay" contains a high proportion of a mineral called kaolinite. 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.

The term "porcelain" has been used almost since the Roman Era to describe ceramic tile made of light-colored clay containing only a little, if any, iron oxide. To the old Italians the resulting tile had the the color and luster of the much admired shell of the porcellana crab. So, that's what they called it: porcellana. The French corrupted the word to "porcelain" and we adopted (the French say "purloined") the French word.

Tile clay is combined with other materials such as feldspar, silica, alabaster, bone ash and water into a mix called a "paste". The paste is formed into a "biscuit" or "bisque" — the body of the tile — and heated to a very high temperature in a kiln using a process at least 3,000 years old.

All clay tile is fired the same way. 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 vitrified by firing.

Firing drives out water and crystallizes some of the molecules in the clay into a form of low-order glass. The process is known as "vitrification" — which is just a fancy name for turning something into glass. The glass is not actually very good glass, but it doesn't have to be. It has to be just "glassy" enough not to absorb water.

How much clay 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 vitrification occurs: resulting in a denser, harder, glassier product more resistant to water absorption. Light-colored clays can be hard fired, as can more common terra-cotta clays. The color of the clay makes absolutely no difference to the firing process. Fire does not care about color.

So, our first definition of porcelain — the traditional or European definition — is a tile made from light-colored clay. It is the color of the clay that defines porcelain for Europeans. The tile may be hard, or not; fired for a long time, or not; 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 was made out of light-colored, porcellana clay 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. It derives from the particular American experience with fired clay products.

In the U.S. there are essentially three separate and distinct ceramics industries: tile, dishware/pottery, and sanitaryware. There is almost no overlap. Makers of fine china do not make toilets, and toilet manufacturers do not make floor tile. This is a little curious because all three industries 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, or floor tile — and then fired at high temperature to harden the clay.

In the early days, tile makers rarely made traditional porcelain tile. If someone wanted porcelain tile, he got it from Europe. But, the other clay industries adopted European porcelain very quickly, and their products soon earned a reputation for being of exceptional quality. By 1917 Lenox had replaced various European companies as the purveyor of fine china to the White House. American Standard had indeed established the "American standard" for nearly faultless porcelain bathroom fixtures by the turn of the 20th century.

When American tile makers needed a word to describe their better-quality tile, the word "porcelain" was available and already well-established in the minds of the buying public as describing ceramic products of exceptional quality. So, they stole it, and "porcelain" became the term reserved for better quality American tile. There is some evidence that American porcelain tile followed the European practice of using only light-colored clay for a few years. But, over time the 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.

So, in the American tradition, the defining characteristic of "porcelain" tile is the quality of the tile, not its color. The tile may be of any color — color does not matter, but it must be a tile that is considered by its manufacturer to be a high quality product.

Full-Bodied Porcelain
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 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 a deep red terracotta 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. Some Silly Porcelain Myths
A number of myths have grown up around porcelain, most of them utter nonsense. Here are a few of our favorites.

• Porcelain glaze has a depth and luster not available on ordinary ceramic tile The truth is that glaze is deep and lustrous if the manufacture applies a thick coat of lustrous glaze. It makes no difference what it is applied to. Glaze can be applied to clay tile, steel, iron, pottery, china, even concrete — in fact, just about any material that can stand the firing temperature.

• Porcelain tile is made from a special "refined" porcelain clay. Horse patootee. Of course, each manufacturer has its own "secret formula" for tile, but there is no universally recognized special clay mixture used to make porcelain tile. But, this fact has not slowed the many "composition" myths surrounding porcelain tile. These suggest that the clay formula used in porcelain has some special or unique properties. We have seen statements that porcelain contains "at least 50% feldspar", or is made of pure kaolinite "cleansed of all impurities", or consists of a "special sand-like substance" (a "sand-like substance", when heated in a kiln produces glass, not tile). Here are some of our favorite variations of the composition myth found just recently on the web from folks who should know better:

• "The only difference between Porcelain tile and regular ceramic tile is that the clay used in porcelain tile is more highly refined and purified. Consequently, porcelain tiles are denser than a standard ceramic tile." HomeAdditionsPlus.com

• "Porcelain tile is a tile that is generally made … from porcelain clays which result in a tile that is dense, impervious, fine grained and smooth, with a sharply formed face."BuildDirect.com

• "Porcelain tiles are composed of fine porcelain clays and fired at much higher temperatures than ceramic tiles." FloorFacts.com

It's all nonsense, there is no special clay formula for porcelain tile.

• Porcelain tile is harder to install than ceramic tile. Any well fired, dense, hard clay tile is more difficult to install than softer tiles not fired as long. Hard tiles are less porous and may, but do not always, require a special setting adhesive to bond well to whatever surface they are being installed on. They are also denser and harder to cut with diamond saws. These characteristics apply to any hard fired ceramic tile. Nor does porcelain require any "special tools" to install as suggested by some "experts", see e.g. FastFloors.com.

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

• The European definition that refers to any light-colored tile body 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.

Because American porcelain is high-quality tile it is often more expensive than foreign-made 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 had no luck.

Rating Ceramic Tile

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 what makes up porcelain tile. Does it require a specific type or color of clay, or a special tile-making process unique to porcelain? But, no, they haven't. And, if they had, it would probably be useless since there is no possibility of getting universal agreement.

Although tile "experts" sometimes expound at length on the "special" and "unique" properties of the clay mix used to make American porcelain tile, there is, in fact no such special clay mix (See sidebar). There are absolutely 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 give a hoot one way or another.

Nor does anyone particularly care about the process used to make the tile. Any manufacturing process that will work is just fine. The tile can be shaped by machine, or by hand; by using huge high-pressure presses, or as an extrusion, or by hand-globbing the clay mixture into a form. The tile can be fired using the old tunnel kiln, or the newer roller-kilns, or a kiln at the local high school. The standards don't care how you make the tile.

All the testers care about is how well the tile functions. Standards used to rate fired clay tiles are all performance standards.

Ceramic Tile 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 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 resistant a tile is to surface 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 wear resistance is important because a hard tile is less likely to show wear after normal use, and is especially important in floor tile used in high traffic areas. 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 will 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 surface wear resistance. It involves applying steel ball bearings and aluminum oxide 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. 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. Rectified Tile
When the guy at the tile store tells you that the tile you are looking at is more expensive because it has been rectified, it sounds pretty ominous — like someone's been naughty and sent to the principal's office. Just what does he mean?

Tile that is fired at very high temperature loses most of its moisture, causing the raw tile bisque to shrink. Shrinkage is very controlled these days so that the finished size of the resulting tiles is very uniform — usually less than 1/16th of an inch difference from tile to tile. But, if the tile has to all be exactly the same size, it is "rectified" by cutting all the tiles to exactly the same size on a saw or grinder. This extra step adds a little to the price of the tile

Rectified tile is for special applications and is just not needed for most home uses, so don't pay for it unless your tile installer insists your need it. Most often, you won't need it.

Class	Application
Group I	The softest tile. Suitable for walls and hobby crafts only, no floors.
Group II	Residential 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 III	All 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. Suited for residential floors that get a lot of use and for exterior applications where there is not a hard freeze in winter.
Group IV+ (or V)	The hardest tile. Extra heavy, high traffic, 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 or countertops, 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.

As we explained earilier, "vitreous" just means "glass-like". So, don't get waylaid by the fancy name. A vitreous tile is generally contains more glass crystals and is more glass-like than a semi-vitreous tile, which is more glass-like than a non-vitreous tile. An impervious tile is more glass-like than all the rest, but instead of calling it super-vitreous, the creators of the test settled on "impervious". But, while impervious tile may be the most glass-like tile, it is not 100% glass. It's just enough glass to be essentially waterproof. Most of the tile is still clay, and the clay is what gives fired tile its shape, strength and durability.

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

Under pressure from American tile manufacturers and seeking to clarify once and for all time the issue of what is a porcelain tile, the American National Standards Institute in 1988 adopted what it hoped would become the only official U.S. definition of porcelain tile in ANSI A137.1 which 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 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 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 extrusion 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".

The effect is that "porcelain" under the ANSI standard has become just an alternate name for an "impervious" tile. If a tile meets the criteria for being rated "impervious" to water, it may be called porcelain.

American tile manufacturers greeted 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 out of the fray over what is or is not porcelain tile. Consequently, imported tiles generally adhered to the European tradition — tile is porcelain if it is made with light-colored clay and its manufacturer elects to call it porcelain.

But, in 2012 the ISO finally caved in. The ISO 13006:2012 standard that defines and classifies ceramic tile established a definition of porcelain tile, adopting with minor variations the same definition as ANSI — 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 test — why let the ANSI guys have all the glory, right?)

So, finally, everyone is on the same page and there is a universal definition of porcelain that every tile maker has to observe. Right? Nope. Sorry. Wish it were that easy.

If tile was required to be rated by law, then the standards defining porcelain would virtually eliminate any issue about what is or is not porcelain tile. But, both ANSI and ISO standards are completely voluntary. No tile maker is bound to observe them. And 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 standards for porcelain.

So, this attempt by the standards organizations to create a universal standard for the use of the word porcelain as applied to ceramic tile has really had very little effect except to further muddle the issue. Many tile makers ignore these new standads, especially traditionalist manufacturers in Europe and South America who still adhere to the older color-based, definition of porcelain tile. And, while many American tile manufacturers have tried mightily to get the ANSI definition enacted into federal law, Congress has so far been busy with weightier matters: mostly getting re-elected and calling each other names.

How to Actually Buy Tile
Glaze vs. Enamel
In the tile world, the glass finish applied to ceramic tile is called the "glaze". In the bathroom fixture industry, the glass finish is called "enamel" — hence the term "enamelware". The two terms mean exactly the same thing, but there is an historical basis for the different names.

Contemporary Silver and enamel broach in the style of Art Nouveau. Available from Amazon. The traditional term, going back centuries in the jewelry-making trades, for glass applied to metal was "enamel". The process involves grinding glass into powder and mixing it into a slurry that is painted on the metal, then fired to melt the glass. It is not only beautiful, but is the ideal material for protecting steel and iron from damage by water.

In earlier times bath fixtures were made out of steel or cast iron. In fact, many bathtubs still are. American Standard and Kohler developed the process for applying glass to cast iron on a large industrial scale soon after the American Civil War, which gave birth to the modern bathroom fixture industry. Following the old tradition, the glass was called enamel.

When sanitaryware manufacturers begain applying over-glaze to ceramic bath fixtures like toilets and sinks, the name "enamel" stuck.

Enameled bath fixtures were so superior to the earlier wood and metal products, that the old products were literally driven from the market within a decade. Enamelware was durable, very sanitary, and easy to maintain; and became an instant hit with American homeowners of the late 19th century who were avid for anything hygienic and sanitary (See Arts & Crafts Styles: Craftsman, Prairie and Four-Square Architecture for more information).

Paint manufacturers soon took note of the reputation of sanitary enamelware in the public mind, and seeking to capitalize on the name, started calling some varieties of their more durable paints "enamel". Today the term is still used but has become essentially meaningless. Almost all modern paint is durable, chip resistant and washable, so there is little to distinguish paint that is called "enamel" from paint that is not.

Fixture manufacturers were a little miffed when the paint guys tried to steal their glory, and fought it for years. They lost. Paint companies were permitted to call their paint "enamel". Today, sanitary fixure manufacturers call their glazing "porcelain enamel" or "vitreous enamel" to distinguish it from that inferior stuff the paint companies sell.

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

A light bodied tile of any quality,
OR
A high quality (in it's manufacturer's opinion) tile of any color,
OR
A tile rated "impervious" by under ANSI standard A137.1 or ISO 13006 defintion of porcelain tile.

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 tradtion may be of any quality. In fact, it does not tell you much of anything useful about the tile. The term "porcelain" is completely ambiguous. If the tile meets any of these 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 completely ambiguous and largely made-up distinction between porcelain and other ceramic tile actually makes choosing tile much, much easier.

Concentrate on the size, pattern, price and color that works best for you in a tile rated for the use you intend it for. Ignore whether the tile body is tan, orange, red or brown. After the tile is installed you will usually never see the actual body of the tile. What you will see is the tile's glaze.

The Tile Glaze
Some fired clay tiles, quarry and saltillo tiles, for example, are not glazed. 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 (or "monocottura") 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. This is called a "bicottura" or double firing method. 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 is a wood fiber and gypsum cement composite.

The same is true of glazed tile. Once tile is installed you can't see the tile body, you see only 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.

By the way, 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.

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, often 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.

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.

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 at least 1/4" thick. Thicker is generally better. If the tile is glazed, then it is the glaze coating that is tested. If the tile is un-glazed, such as in quarry tile, the tile body itself is tested. If this rating is missing, the tile is probably not intended for floors — and will usually say so right on the box.

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, vitreous tiles can be used outdoors — not recommended in Nebraska, however.

A tile rated "impervious" to water absorption may be called "porcelain" under the ANSI standard for porcelain and may be certified by the Porcelain Tile Certification Agency, a trade group, as "porcelain" under the ANSI definition. It does not have to be certified, however. It is the manufacturer's option.

All tiles called "porcelain" do not necessarily rate "impervious" in this test. Don't rely on the word "porcelain" on the box, look for this specific test rating or the PTCA certification of "porcelain".

For floor tile, this Coefficient of Friction (COF) 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 can airily skip down slippery slopes that would kill us clumsier types, this test has some basic reliability problems. It has not been adopted outside of Europe.

If present, the "Frost" icon merely tells you that the tile is able to withstand repeated cycles of freezing and thawing. If there is no frost icon, it may mean that the tile is not suitable for use outdoors in any place where it might freeze, or the tile maker did not bother to order the test. A more reliable guide is the tile's rating on the water absorption (W.A.) test, above, for which almost all tiles are tested.

The tone and shade rating is an indication of how much variation there is in the color and shade of the tile. The range of ratings on this "V" scale is V1 to V4.

	V1 indicates low visible shade and texture variation within each carton.		V3 indicates a high shade and texture variation within each carton.
	V2 tile show distinguishable differences in texture and pattern within each color.		V4 file contains random variations of shade and texture within each carton.

Grades V3 and V4 need to be continually blended during installation to insure optimum appearance. This generally results in higher installation costs. Also, examine more than one tile, and more than one box of tiles to see if you like all the various tones. There may be considerable variation between cartons.

Some Informal Quality Tests
How did we tell good tile from not-so-good 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 than 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 your thumb and 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 more vitrified 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 COF 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 your 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.

The Informal Mohs Scratch Test: In 1882 a German mineralologist, Friedrich Moh, developed a table of relative hardness of minerals which has since become well-known as the Mohs Scale. Each mineral was given a number, with talc, the softest mineral ranked as 1, and diamond, the hardest, ranked 10. The minerals are:

Rank	Mineral	Substitute Test Material	Rank	Mineral	Substitute Test Material
10	Diamond		5	Apatite	Window Glass
9	Corundum		4	Fluorite	Pocket Knife Blade/Steel Screw
8	Topaz		3	Calcite	Copper Penny
7	Quartz	Case-Hardened Steel File	2	Gypsum	Fingernail
6	Orthoclase		1	Talc

Each mineral in the table will scratch any mineral ranked lower in the table, but will not scratch any mineral ranked higher. Since most of these minerals are a little hard to come by in daily life (just what is "fluorite" or "orthoclase", anyway?), substitutes are generally used for the informal Mohs scratch test. These are shown in the table above. The substitute will scratch any mineral lower than its place in the table, but will not scratch any material higher than its place in the table.

Wall tile should have a Mohs scratch resistance of at least 4. You should not be able to scratch it with a copper penny. Floor tile should be at least 6 (7 is better in high traffic areas). You should not be able to scratch floor tile with a piece of ordinary window glass. If even a case-hardened steel file does not scratch the tile, it's some kind of alien super-tile, possibly escaped from a secret government lab in Area 51. Check for radiation!

For comparison, vinyl floor tile and vinyl sheet flooring is Mohs 1-2. You can dent it with a fingernale. Site-finished wood flooring is Mohs 3 and can be scratched by a steel screw or pocket knife, but not with a fingernail, and rarely with a copper penny. Marble is typically Mohs 3-4. Engineered quartz countertops are around Mohs 7-8 — tough stuff that can be scratched only with a case-hardened file. Natural granite tops out at Mohs 4-5. Some can be scratched with window glass, but not with a pocket knife.

Do not scratch a tile without the store clerk's permission. In fact, you may not have to scratch it at all if it has a Mohs rating printed right on the box, and many tiles do. If the clerk does not give you permission, buy just that one tile, then see what will scratch it before committing to more.

Don't Rely On Informal Tests. These rule-of-thumb tests should not be relied on by themselves. Read the ratings on the box. But, you can use these to impress the sales clerk with your deep and comprehensive knowledge of fired clay tiles. It helps to throw around words like "monocottura" and "bisque" while you're at it, and refer frequently to ANSI A137.1. You'll have the guy on the run after just a few minutes.

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 fired clay tile.

Don't	pay any attention to the word "porcelain" on a box of tile. It does not tell you anything particularly useful.
Do	read the ratings on the box. Even if there are no handy icons, the ratings are probably in the fine print somewhere. If there are none, pass it by. You do not want to buy untested tile because you have no idea what you are getting. If you have questions about a rating or whether a tile will work for the application you have in mind, ask them of the manufacturer, not the clerk. The clerk probably knows less about it than you do after reading this article.
Don't	buy a better tile than you need. If you buy an impervious tile for your shower walls, you have probably paid more for features you don't need such as very high wear and frost resistance. A semi-vitreous tile would work just as well, and most likely cost less. Of course, if you just found the tile sale of a lifetime, forget all this.

So, is it Porcelain or is it Ceramic?
We don't actually care, do we?

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 ploy 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 — deceivin' scoundrel that he is.

A Little Something to Take to the Tile Store
OK, so now you know how to buy tile. If you read this article carefully, you also know more than 95% of tile store clerks. So now for the piece-de-resistance, here is our handy How To Read a Tile Label crib sheet that you can download and print to take with you to the tile store.

Happy tile hunting. Let us know how it works out. And, don't forget to rate this article, below. Also, take a look at our other in-depth articles on remodeling topics and issues. The complete list is in our Index to Articles. Have fun. We do.

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Rev. 6/06/12