How is Italian marble polished

marble

Shiny limestone

All decorative limestone that can be polished is colloquially referred to as marble. They mostly consist of calcium carbonate. This calcium compound is of organic and inorganic origin: Calcareous deposits, such as coral reefs with the community of plants and mussel animals from the primeval oceans, have found their way into different layers of the earth through tectonic movements over the course of millions of years.

Where this calcareous rock was pushed into the interior of the earth, it came under high pressure and had to withstand extreme temperatures. The limestone crystallized and became real, crystalline marble over the course of millions of years.

In areas where the limestone was shifted less deeply, exposed to less pressure and a lower temperature, crystallization did not occur. This geologically younger limestone can also be polished and is therefore also known as marble.

It is not as hard as the crystalline one, but it is very colorful. The term "marble" for the different qualities has more to do with the common property of having a polished shine: In Greek, "marmaros" means shiny.

Import hit since ancient times

Marble can be found in many regions of the world: for example in Italy, France, Belgium, Germany, Greece, Spain, Portugal and Turkey, but also in Iran, India and China. In each of these areas the marble has a different quality.

It differs in color, structure and hardness. Each mining area therefore has different customers who manufacture different products from it. This is also the reason why Italian marble from Carrara is also used in France, although there are also marble quarries there. Marble is always imported when it comes to a certain quality or color. That was already the case in ancient times.

There was a real marble cult in ancient Greece. This was not only because the stone was suitable for magnificent temple buildings, but also because it could be found there in large quantities and in many places. The high-quality marble from the island of Paros and the Pentelikon Mountains on the Attica peninsula was famous.

This Greek marble also adorned Roman temples up to 100 years before Christ. It was exported. That changed when the Romans discovered their own marble in the Apuan Alps of Tuscany. Settlements for slaves were established, such as Luni.

For example, the Pantheon in Rome, the Forum of Trajan and the Trajan Column were built from Luni marble. The Roman Emperor Nero declared all newly discovered sites to be state property, including those in Gaul, now France. There were many colored marbles there, which the emperor liked better than the white ones from Luni. With the fall of the Roman Empire, the mining of the marble deposits came to a standstill.

It was not until the 15th century that the precious stone began to be used again in the Renaissance. A particularly beautiful marble was discovered near Carrara in Tuscany. Carrara marble is brilliant white and therefore particularly suitable for sculptures.

"Statuario" is the name of the variety made famous by Michelangelo's statues. Due to the purity of this white stone, there is not so great a risk that it will crack during processing. Today Carrara is considered to be the only mining area in the world for this pure white and expensive Statuario marble.

The marble quarries in Estremoz in eastern Portugal, not far from the Spanish border, are also gigantic. They are among the largest in the world. The colored marble lies just below the surface of the earth. That makes dismantling easier. It can be found in three places: in Estremoz it is marbled pink, in Villa Vi├žosa it is white and in Borba it is brown to reddish. The marble of this area is mainly used for the production of tiles.

Laborious dismantling

How can a cuboid block be cut out of the massive stone wall of a mountain? Over the centuries, better methods have been developed to break out blocks in a calculated and controlled manner. But it has remained dangerous to this day.

The Romans still had to accept a lot of waste with their method. They drove iron wedges into natural cracks and crevices in the rock until a block broke out. Wooden wedges were also driven in and kept constantly wet. This caused the wood to expand and put enough pressure on the rock to burst it. This termination method was in use for a long time.

The misshapen pieces were then cut into rectangular blocks and brought down to the valley. That meant you just let them roll down the steep slope and wait for them to come to a standstill somewhere. Later wooden rails were laid. The marble block then slid down the slope in a targeted manner, held by ropes.

Even so, there were always fatal accidents when ropes broke and blocks fell unexpectedly. Each block of marble was attached to the axis of a wooden drum and rolled for transport over several kilometers. An elongated cuboid was connected to two wooden drums like an axis. Oxen pulled the cargo or slowed it down when it went downhill.

In the 18th century, the rock began to be blasted with gunpowder. This made degradation much easier, but not easier to control. Holes were drilled in the marble and hydrochloric acid was poured into them. The acid-sensitive limestone was hollowed out at this point, into which the explosive powder was filled and ignited.

Of course, much was destroyed in such an explosion. Large heaps of rubble were created. In 1896 there was a new, completely revolutionary method. The marble block was now cut out of the rock with the help of a circumferential, spiral-shaped steel cable.

The principle: First you drilled a horizontal hole in the rock wall and then you created the connection with a second hole from above. The steel cable was passed through this connection. Silica sand was used as a cutting agent and water to cool and rinse the joint. For the first time, precisely calculable cuts were possible.

Another important improvement came around 1980: the diamond-studded steel cable. Technical diamonds, which are firmly anchored in the rope at regular intervals, replace the sand as a cutting agent. Today, laser-controlled machines are used to process the blocks, which can cut 30-ton blocks with millimeter precision.

Bulldozers for removing the blocks weigh around a hundred tons, have tires almost three meters in diameter and can easily move huge blocks. It is still dangerous in the marble quarry today: when a steel cable breaks and the diamonds fly through the air like projectiles or when truck drivers maneuver the truck over serpentines with enormous inclines and frightening slopes through narrow, rain-soaked hairpin bends.

Diverse marble

Large sculptures made of white marble are rather rare today. But wherever there is to be represented, marble is used. As wall cladding in large reception halls, in stairwells, entrance areas of exclusive hotels and increasingly also in private apartments and houses. Bathrooms are fitted with marble tiles.

Marble floors in living areas do not have to be cold either if they are above underfloor heating. Terrace slabs, outside stairs, sculptures in the garden are not damaged even in severe frost. Since marble has a very small pore space or a very smooth surface, it is extremely frost-resistant. It proves this quality as a tombstone in cemeteries.

Marble is less suitable for the kitchen because it is sensitive to acids. It reacts to vinegar, wine, citrus fruits and strong cleaning agents with stains. But industry already has a means against it. The marble comes in a bath that closes the pores against all harmful influences. A plastic coating, on the other hand, is more useful than beautiful, as is the case with the small, round bistro tables.

In addition to the aesthetic purpose, there is also the technical one. Marble powder is used as an abrasive, in the finest form also as an admixture in toothpaste. The pharmaceutical industry makes calcium supplements from it, such as tablets for allergy sufferers or to promote bone formation.

In the past, the local marble works sold their remains to industry, which used them for technical and pharmaceutical purposes. Today these industries have their own quarries.