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29 April 2011

Thursday 28th April 2011; Working Techniques of Stone

Week 3 of 12
Module 3: Material Characteristics and as a Building Material

The sculptor Peter Rockwell this morning introduced us to 'Working Techniques of Stone' and this afternoon took us to some of the famous sites in Rome to illustrate his lecture; Basilica di Santa Maria sopra Minerva, Pulcino della Minerva, Pantheon, Piazza Navona and the Fontana dei Quattro Fiumi. He methodically introduced us to the different tools available to masons both in Italy and abroad and explained how the types of tools used have varied according to history and location. Peter explained the differences we may see between the finishes on sculptures including a true polish (a painstaking process of hand-polishing stone using various abrasives) and a false polish (wax applied to the carved surface of the stone- often resulting in brown staining).

I have always thought of sawn stone being a (relatively) recent development for masons, however the earliest known saw cut in stone was in Egypt in the 3rd Millennium BC. Commonly the saw that is used on a stone will not have a sharp blade or have 'teeth', but a water and abrasive mix is dripped into the cut and the stone is abraded away by the moving saw.

Stone workers / masons use geometry as a tool for calculating angles and designs rather than arithmetic- callipers are used as an instrument for measurement. Simon Warrack commented that he had once asked his teacher when he was an apprentice stone mason if his straight line was good and was told that something either is a straight line or is not a straight line, but there's no such thing as a good straight line. Most carved work that is composed of more than one piece of stone usually has a rough margin left so that it can be finished in place, because inevitably things will not line up as expected. We were shown how an unfinished piece of work- and the stage at which it has been left, can be identified by examining the tool marks present on the stone.

Peter presented the interesting case study of Easter Island which I believe was inhabited in the 4th Century AD and no-one else arrived on the island until the 18th Century. The forms of quarrying and stonework are therefore considered to be indigenous and show an interesting development in techniques. No metal was available on the island and therefore the harder stones were used as tools for working the softer stones. Easter island is famous for its mo'ai statues of which there are c.800 on the island- c.300 of which are unfinished. This gives us a fantastic insight into the stages of their creation and it can be seen that a large amount of the carving would have been done with the stone in situ in the quarry until it was necessary to move it to complete. The largest sculpture is 20m in height, although this one has not been moved from the quarry. The largest standing is 9m in height.

Many statues break at the ankles/legs because this is their weakest point. It is believed that the Ancient Greeks did their carvings horizontally on the ground and then stood them up to reduce the risk of breakage, whereas the Roman sculptors would have carved theirs standing up but incorporated a support into the design- commonly a tree trunk.

The grave of Andrea Bregno, a sculptor, is within the Basilica di Santa Maria sopra Minerva and the tomb has been decorated with many carvings of masons tools.

The ceiling in the pantheon, one of the few examples of a truely Roman building including most of the original, marble walling columns and flooring, the cast 'Roman cement'  dome and brass doors. All as stunning as hoped for.

Fontana dei Quattro Fiumi (Fountain of the Four Rivers), 1651, designed and partially sculpted by Gian Lorenzo Bernini representing the World's for largest known rivers; Río de la Plata (S. America), Danube, Nile and Ganges. The base is formed of Travertine and the sculptures are white marble.

Close-up of 'Danube' who holds an oar to represent the longest known navigable river. The original tooling marks are visible on the oar and on some parts of the torso.

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