What is Quality in Dimensional Stone

by | Oct 4, 1994 | Articles

Originally Published in 1994

For years the question of quality has always been an issue in the dimension stone industry. Is “quality” texture, color, ceramic, natural, defined, standardization, legal, or perceived? Many people ranging from architects to contractors, suppliers to fabricators have asked what is quality? People have gone to court to determine the quality of a stone or installation. Many times people have perceived that the stone is poor quality and this is why failures occur. Failures in stone are usually understood to be an issue of the quality of the stone. Others have attributed the color variation of the stone as a quality concern. When a stone has cracks, fills, veins, or has mesh backing, or glued together, or other natural inherent characteristics it is considered poor quality. WRONG

Is Quality: Texture?

The first thing everyone must admit is that stone is a natural product formed in the earth under pressure for millions of years. We stone people come along and take it out of the earth because we think the color may make it sellable to an architect or buyer for a specific application. Thousands of millions of dollars are spent to extract the stone and work it for resale. Some people make money quarrying the stone only and sometimes this is considered the most profitable part of the stone business. Others make money cutting the raw blocks into simple tiles and slabs. Still other manufacturers work the stone into intricate patterns, designs, statues, moldings, columns, furniture, specialty items and so forth. Everyone is looking for a way to capitalize on the raw material and transform it into something the buyers will want. Buyers are always looking for different stones and have demanded so much that there are now thousands of quarries trying to satisfy every color palette under the rainbow to give the buyers what they want. Some buyers will find a stone ugly while others will find it beautiful. The tastes of buyers in the world differ so much that it is not easy to guess what will sell or not sell. These tastes vary from one section of the country to another.

In past years buyers wanted mirror polished stone for flooring. Today the trend is rustic flamed or honed stone. Rustic may even mean that the buyer wants cracks to appear in the stone to make it look more aged and antique. Factories are appearing now to specialize in the making of antique stone. For years producers have fought to take a stone which is natural and make it modern looking. Now they are being asked to take a 20 million year old stone and transform it into a product which looks old naturally. This is true irony.

Suppliers have worked with machinery manufacturers to take the stone and treat the surface of the stone in many different ways. Stone can vary with such finishes as flamed, sandblasted, polished, honed, acid washed, cleft, sawn, water jet, and liquid antique to name a few. Each stone may flame or polish differently. Some stones will not take a mirror polish well. As it is the nature of stone to have different degrees of hardness and abrasive resistance and contain hard and soft spots within the same face of the stone, it only shows that the stone can vary in the degree of finish. It is this natural difference that gives a specific stone the warmth and texture that architects and buyers want. It is the nature of dimension stones to exhibit variation. A stone which is polished may not appear to look similar to itself when flamed.


Is Quality: Color?

Buyers have taste in colors that vary so much that no one really knows what colors sell internationally. Color is determined by the amount of certain types of minerals or feldspars or impurities. Certain colors that may not sell well in North America do sell well in the Far East or Mid East. Buyers have selected stone in the past due to the color variation a stone portrays. Now some buyers want the same stone but only 5% of the production as they may not want to see all the color variation but only a select portion of it. Some stones require 20 samples to show the color range while others you can see the overall appearance with two samples. The ability of a supplier to control the color to the limitations and expectations of a buyer varies. This limitation may be achievable or may not. It may be a consideration of cost or time. It may be limited to a smaller size. The limitation of color in supply is more of a factor of the supplier than the quality of the stone. In any case, a buyer should never determine the selection of a stone from a mere photograph or one small sample.

In a recent study in France on color it was noted that the human eye can distinguish over 785 color variations. Thus even the ceramic producers who try to control production by color lots and mark the boxes with color codes are themselves showing the difficulty to match and control color. How can natural stone be controlled in color?


Is Quality: Ceramic? 

Some stone producers sense that the buyers are being dictated by the ceramic industry. In ceramic the color is matched very well to the buyers needs and the consistency and uniformity of the product is well known. How can buyers expect that of a natural product like stone? Why even select stone if you want a vinyl or ceramic look. In fact, now the big push by ceramic tile producers is to make ceramic tile look like limestone, granite, and marble. The problem they have is to match the beauty and warmth of natural stone. The ceramic producers will keep searching for the ideal product they can produce to look like stone which will give them a larger share in the market taking away sales of natural stone. Richard Dray of Richard Dray Engineering calls this attempt by ceramic producers as a way “to provide predictable patterns, perfect color matches, reliable supply and known physical characteristics more economically.” This attempt to duplicate natural stone is very difficult in its entirety. However, since this is a buyers market and there is so much competition many ceramic producers will keep trying. They will succeed eventually as this is a credit to man and the innovations of technology.


Is Quality: Natural?

What makes the stones different? Some stones are different because of the granular structure like dolomites, whereas Calcite marbles have a mosaic structure. The metamorphism of the stone causes certain impurities such as clays and quartz to react with calcite and dolomites to form minerals such as garnet, talc and olivines. The presence of other minerals such as iron oxide produces red colors; chlorite and epidote a green color; and graphite a blue color. Some stones are from mountain tops while others are underground or from old river beds. Some stones will have fossils in them showing the true age of the stone. Some stones have open seams or veins that open when exposed. A few factories will leave these natural occurrences alone while others will fill the voids or holes with matching colored epoxies. Many stones have cracks or are inherently weak and will break when put under the pressure of the polishing machine so some factories put a mesh backing on the stone to hold it together. Many green stones warp when not under the pressure of the earth. This is due to their cellular structure. None of these issues deal with the quality of the stone. Some of these issues must be addressed however in the production or installation of the stone and the buyers must be aware of this as well.

“Marble owes its beauty and strength to the skeletons and shells of countless millions of tiny sea animals called crustaceans and is made of calcium carbonate. Onyx are calcium carbonates deposited by water. Verde antiques are marbles made up chiefly of serpentine, a hydrous magnesium silicate. There are three major types of rocks quarried: igneous, metamorphic, and sedimentary. Marble, quartzite, gneiss, and slate are metamorphic. Sedimentary rocks are shale and sandstone, while granite is igneous rock usually containing quartz, feldspar, mica. Limestone comes from sea shells and corals whose chief by product is carbonate of lime and is a sedimentary rock. Travertine is really a form of limestone. Slate and shale have predominant minerals such as mica, chlorite, and quartz.”

There are so many different stones with varying degrees of hardness or abrasiveness that not all stones polish with the same mirror polish that a buyer may expect. Many stones have different degrees of absorption which will affect the long term maintenance of the stone or make the stone perhaps not suitable for certain exterior applications or flooring applications. Some stones will fade in color when in direct sunlight; while other stones will spall or chip or peel when water is applied to them like Negro Marquina; while other stones will effloresce when water is used on them like some of the Taiwan green marbles. Some stones such as slates or sandstone’s do not split evenly when cleft finishes are required so the variation in thickness can be a lot more than expected or the face of the stone can be more or less variation. All these occurrences are natural and quality is not an issue. There are over 5000 different stones from over 34 different countries. The buyers are strained to know all the variables about each stone.


Is Quality: Defined?

Defining quality should be to understand what issues are not quality concerns. Quality should not be considered as the nature of a product to exhibit its own characteristics. Natural stone can not be made artificially or reproduced in a laboratory. It is natural and this is why buyers have selected it in the first place. The Marble Institute of America years ago started to classify marble by grades A-B-C-D as a soundness classification. “A” was to mean a very consistent stone with a sound structure which did not require gluing or fixing. “D” stone was a marble whose characteristics required sometimes gluing and exhibited a lot more color variation. None of these soundness classifications had anything to do with quality. A “C” stone could be used on floors or walls and once installed properly would perform its function as well as a “B” stone. However, today many architects are trying to define their needs as wanting an “A” marble of which there are very few “A” marbles in the world. In many architects minds they consider “A” to mean quality for which this was never intended. The elements of design are the line, color, value, space, mass, and texture. The architect will use these elements to design a building and select a product such as stone to suit these elements. As there are many design tastes there are also many natural stones which can be selected to suit most design elements. The oldest known examples of architecture are in Egypt and are made of stone blocks called pyramids.

The market in stone has never agreed on defining quality in stone. In past years, for example, I have spoken with numerous producers or fabricators of stone. In each case one claimed to produce better quality than another producer. No one agrees what is a quality polished edge or a bullnose edge. Each producer says he can do a better job than his competitor. Since the machines to produce the labor items as well as the workers techniques vary from shop to shop, it is easy to see this contradiction in what is so called quality. What is acceptable workmanship must be determined by the buyer as it is in the furniture industry. In furniture, there are different manufacturers of sofas and perhaps one is better quality than another, but who is to determine the standard of quality and rate it or define it.


Is Quality: Standardization? 

Recently Europe has introduced ISO 9000 which is being implemented in many countries. It is trying to define “Quality Standards” yet in the United States this presently is called Q90 released by ANSI/ASQC and is a complex set of requirements to help establish a unified quality policy in manufacturing. However, how this applies to the stone industry is obscure. The system of ISO 9000 is primarily a paperwork one in which the standards of management, principles, marketing, procurement, test equipment, corrective action, personnel, product safety are all quality issues. No attempt has been made at defining the quality of stone as it is natural. The procedure a company follows to produce a product and sell it and stand behind it are the real issues. “Quality control is a system for verifying and maintaining a desired level of quality in a product or process.” However, it does not define quality in stone except to say it is “character with respect to grade of excellence…” This ambiguity in terms of defining quality is confusing as natural products such as dimension stone has been used for exterior or interior applications due to its quality which really refers to integrity or the ability to withstand the natural elements or man made elements.

Quality has to be definable. A.S.T.M. defines in section C119 standards for terminology in stone but says nothing about quality. It further defines the standards of testing stone and the results for physical requirements as it relates to matters which can be tested such as abrasion, compression, absorption and so forth. These are all definable and controllable. The results of such testing can be used to define the integrity of the stone for a specific application. Certain results of testing can then be made to make sure the stone will perform within minimum standards. These standards set by A.S.T.M. are accepted generally as a guideline only to what should be used as a minumum for a specific application. If a stone does not meet the standard it does not mean it can not be used. It only means that engineers and architects will need to determine the thickness, or anchoring method, or sealant, or maintenance, or limitation in size that will work with this specific stone for their application. Stones, for example, with higher absorption have been used on exterior high rise cladding even though they have a higher than acceptable amount of absorption. Further, the amount of testing done on a stone during its manufacturing process varies thus some stone may pass certain standards while the same stone may not pass in other areas. All the tests that may need to be run on the stone are not necessarily performed nor are the standards even addressed by A.S.T.M. such as the affects of sun on coloration changes on the stone. The industry is growing and learning. In time more standards will be invented and need to.


Is Quality: Legal in Stone?

There is a legal issue in the word “Quality”. In old legal documents it was called Caveat Emptor or “Let the buyer beware”. Since our economy has grown we have become protective of the consumer and thus the legal system has established not only express warranties, that which is written and defined on the product, but also implied warranties, or that which implies a quality of the product that makes the product suitable for which it was sold. The U.C.C. or Uniform Commercial Code states that “every sale implies warranties such that the goods are fit for the purpose you had in mind in making the sale and that if you ordered from a sample or a description, what you will receive is like the sample or is as it was described to you.” It is therefore up to each sales person to know the product he or she is selling and know where it should be used and where it should not be used and how it will perform. The samples shown to make a sale must represent the material being sold. This, many times, is most difficult for various reasons. Sometimes this is difficult since some stones vary a lot in color, or have holes, or carbon spots, or cracks, or fills and therefore besides a sample a clear written description should accompany the sample.

Quality must be defined in workmanship of the stone to assure the quality control as may be established by such standard documents as the M.I.A. Design Manual. In this manual you can refer to tolerances in size or thickness, or to the installation method, patching of stone, A.S.T.M. standards of stone performance, warranty, and maintenance of the stone. These have been defined and can be used for reference. If specifications such as outlined by the M.I.A. or A.S.T.M. are tied into the contract of sale or purchase orders than perhaps their is a legal basis to revert back to this document as a way of stipulating the quality controls that were to be expected. It is common practice that most buyers do not presently do this.

It should not be the place of the buyer to look at stone and because it has natural flaws or not the exact color they expected to imply the quality is poor. There are selections many times within a stone family that may give the buyer less or more color variation. The natural flaws of a particular stone are natural and can not be normally avoided. In any case this is not a quality issue. It is a selection issue. If the finish on the stone does not match the sample then perhaps the quality of workmanship was not controlled. Some stones are difficult to polish evenly and with uniformity as they may naturally have, for simplicity sake, soft and hard spots. On filled travertine, for example, to polish the face evenly and give a mirror polish is impossible since the face is stone and cement. Again this does not imply the travertine is of poor quality. Some limestones for instance have an absorption of 20%. This does not imply a poor quality limestone, only that it has high absorption. Knowing the weakness of a stone will allow the buyer, architect, or installer to know how to handle the stone for its intended use.


Is Quality: Perceived?

I once visited a buyer who ordered Crema Marfil. He was rejecting the Crema Marfil due to its poor quality. Upon visiting the client we found out his complaint was the stone showed too much gold veins and had a slightly darker background then he was used to receiving. The supplier and I studied the stone and inspected the size, finish, packing, uniformity etc. and found the stone to be of exceptional quality. In reviewing with the client what he wanted or expected, it was found that there are 3 distinct types of crema marfil. Some of the marfils have a lighter background with light white spots in it, which are very soft and eventually crack, and with less veining. The soundness of this stone is inferior to what he received. The complaint strictly revolved around color and veining and it was determined that in no way was this a quality issue. In fact, it just so happened that the representative of the stone association from the area in Spain where this material was quarried was in town. We brought this individual back to see the product and told him the complaint perceived as “the buyer said this was not good quality”. Immediately, without hesitation, the representative stated the material was of far superior quality. The point of the story is that buyers do not always want quality or do not understand themselves what is quality, but they do know color. Color in many cases is why the stone is selected, besides its texture, or finish, or wear.



Therefore, in conclusion, the industry must now define and relate to buyers the knowledge about the stone prior to selling it. Items that should be discussed and perhaps put in writing are: quality, quality control, color variation, durability, hardness, absorption, warping, filling, cracks, spalls, spots, veining characteristics, how to maintain the stone, how to install it properly, and inherent problems that can be foreseen in its lifetime of use. Many times even the seller does not know all the answers to these issues. However, if we as a group of marble people expect to sell more stone than we can not allow the caveat of “Buyer Beware” or the buyers will eventually not wish to buy stone. The word “quality” should sometimes be referred to in the selling and the knowledge of the stone and not the stone itself