When measured on the Mohs scale (Named after Friederich Mohs, a German mineralogist who invented a scale for determining the hardness of a rock or mineral), the hardness of stone can be compared and measured against the tools available in its dressing.
‘Imperial porphyry’, for example, a deep purple stone from the Eastern desert of Egypt, is a 7 or 8 on the Mohs scale and is one of the hardest stones to have been worked in large scale and will quickly wear out diamond tooling and saw blades (diamond is 10 on the Mohs scale). This porphyry is extremely hard to polish, and incredibly difficult to carve. Examples of incredible workmanship of this stone are a huge circular bath found in the Emperor Nero’s palace, which is on display in the Vatican museum, Rome and ‘‘The Four Tetrarchs’ made in 300 a.d., which adorn the façade of St Mark’s Basilica in Venice. I have great admiration and sympathy for the creators of these pieces; their task would have been most arduous, and taken many years to complete. This particular stone is thought to have been used by the Romans in and from the first century a.d., and there are apparent records of slaves forced to work in the porphyry quarries.
It was a highly prized stone because of its purple colour, and was used solely for the Emperor of the time.
Sometimes a decorative stone can only be identified by a nickname, which refers to its colour, or characteristics, or antique history. Often its origins are unknown and such stones have been frequently misrepresented or wrongly classified. These stones can, however, become the most highly valued, and are often found in important stately homes, in specimen tables, ornament, or inlaid within chimneypieces.
It is surprising how many stones are incorrectly classified; limestones are regularly described as marble because they can be colourful and take a polish, but limestones are sedimentary rocks, and marble is truly a metamorphic rock. It is difficult to determine the true classification without geological knowledge and instrumentation. However, this is perhaps a lesser concern to the stonecutter and his patron who appreciate the natural aesthetic beauty evident in the work produced.
Pietre dura is the Italian name for hard stone inlay, and can be seen in tabletops, pictures, chimneypieces and ornament. The masters of this trade are said to be the Florentine artisans in Firenze, or Florence, in Italy.
Ornate, foliate designs and classical motifs are frequently employed in the design, along with various other flora and fauna. However, the variation, colour and pattern visible in stone can inspire endless possibilities. The process of pietre dura involves the artisan carving out a recess in a background stone, usually Paragona di Fiandra. (belgian black). For example, the outline of a stylised image of a bird or a flower is drawn onto the background stone, and the area within the outline removed. The individual pieces of different decorative stones to make up the bird are shaped and fitted together using wire saws and files.
It could be likened almost to an elaborate jigsaw or mosaic. The individual pieces are then glued into the carved recess of the background marble or cut oit shape and polished flat. The inlay work can be unbelievably skillful, meticulous and awe-inspiring, and in some examples (such as in the Pitti Palace in Florence), visitors are often astounded to discover the images within the tables are made of stone and not painted. Were it not for the simple designs I have since made, I could not have possibly imagined their creation.
The art of pietre dura in particular, has given me a profound appreciation of decorative stone. It is always exciting to discover a new medium or learn more of the history of an existing stone, perhaps through the chance meeting of a mason or artisan who has had previous knowledge of that material, or by discovering a specimen for sale. The formation of all specimens is apparent in their polished state; fossil remains can be seen, veins of minerals can seep into fissures during the formation, pieces of other detritus or foreign stones can be caught up in the matrix, in turn forming a new specimen. Simple limestones, which could be considered common, are also beautiful to behold, especially when they have been carved and cut to form the buildings of antiquity or of the modern world; the stones are in themselves, timeless.
They will remain long after mankind has disappeared.
Evident within these stones are the creation of the earth, the remnants of extinct life, and once violent eruptions from now dormant volcanoes.
Stone is used to celebrate the living, to furnish the home, to commemorate the dead and preserve the image of long dead kings, popes and poets in eternity. The permanence and legacy of an empire or religion is reinforced by its use of architecture.
Where writing did not exist or does not remain, stone carving provides archaeology with a text, an explanation in the form of a bas-relief, inscription or statue of a god or ruler; a temple of worship, or a sacred wall. Timeless and familiar, mankind has sought shelter in ancient caves; he has removed mountains to build castles and homes.
In Peru, the Inca fashioned altar stones mimicking the mountains around them. This fascination with stone is a reflection of a primitive understanding and connection with the earth, which in some part, we have perhaps lost in modernity.
By Matt Hurley, Stonemason, Hurley Marble, Devon
Part 1 of this blog on decorative stone work and architectural ornamentation can be found here.
Examples of one-off decorative marble table tops and fireplaces by Matt Hurley, a Devon based stonemason of 20 years experience can be found at www.hurleymarble.co.uk