STONE project.


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11 Actions and Procedures

Stone Grading

Some quarries produce ‘dimensional’ stone in large blocks.  Other quarries immediately break up the stone for use in roads or as filler. The quarries that produce dimensional stone may even try to salvage the residue.  To be useful, the stone needs to be sorted by size.  Essentially the stone is passed through large sieves. This is the primary quarrying technique in sand quarries, and a secondary technique in quarries harvesting dimensional blocks.

 

Stone seive, Henraux Quarry, Pietrasanta, Italy Spittal Quarry, Watten, Caithness, Scotland

Granite residue, after it is graded, is used for roads and building, or as aggregate. Granite dust is sometimes used as soil conditioner. Marble and limestone residue has many different uses depending on its purity.  It can be ground up and used for medicine, toothpaste, food additives, or filler for paint. Lime has many other uses.

Moving stone

Stone is heavy, and moving it is not a simple matter.  Large heavy weights can be moved by putting rollers, round tubes or pipes under the stone. A very heavy stone can be pushed with relative ease on rollers.  Stones can also be moved on sled, skid or ‘stone boat.’  A block and tackle, or ‘come-along’ can help to pull a stone along. The strain on the cable can be intense. To minimise risk of injury due to cable snap-back, a blanket, tarp or a coat can be thrown over the strained line to absorb any suddenly released tension force.

 

 

 

Once a year in Carrara an ancient technique called Lizzatura is reenacted.  Lizzatura is a preindustrial technique in which large blocks of stone down from the mountain.  Stone Project planned its research visit to coincide with this event, which can be seen on film.

Stone can be lifted using jacks for small elevations or a hoist such as a gantry or crane for bigger open lifts.  A gantry is an A - or H- shaped frame equipped with pulleys.  A gantry will allow slow and careful lifting.  There are different ways of rigging the stone to a gantry or crane.  Often slings are used but there are other options, such as a device called a Split Pin Lewis.

Fork lifts and pallet movers are recent tools that have been adapted to stone use.

Once a year in Carrara an ancient technique called Lizzatura is reenacted.  Lizzatura is a preindustrial technique in which large blocks of stone are carried down from the mountain.  Stone Project planned its research visit to coincide with this event, which can be seen on film.

Cushioning and Transportation

Stone, as tough as it appears to be, has the unfortunate combination of being both heavy and fragile.  Throughout its life cycle it needs to be cushioned again and again in different ways.

When a large block is split from the edge of the quarry its fall is softened by rubble that had been piled under the projected place of impact. This doesn’t always stop cracks but it reduces the possibility considerably.  Various other devices perform similar roles.  Large inflated ‘pillows’ in thin metal are also used.

When a smaller stone is carved it is elevated to a convenient height by putting it on a banker, which is an elevated solid work table.  It is usually made of wood, because wood has a natural cushioning effect.  Occasionally an extra bit of carpet is put on top to further cushion and keep the stone in place. In Croatia the bankers were wooden barrels filled with stone chips.  This elegant and efficiently designed banker has been used without interruption since Roman times.

After the stone is placed on top of the banker, it might need to be supported again with small sandbags or wedges. These are positioned according to the vulnerabilities of the stone. If force is applied to unsupported stone it is more likely to break.

Transporting heavy and fragile objects present unique challenges.  Sometimes stone is packed in sturdy crates surrounded by woodchips or straw.  Styrofoam ‘peanuts’ that are commonly used today for packing lighter objects are not practical for stone because they will flatten under the weight of moving stone.

Larger objects can be strapped to pallets and surrounded with a protective cage.  Allowing part of the stone to be seen seems to add additional protection because the worker moving the crate is reminded of its fragility.

Stone Fixing

Sandstone and limestone absorb water.  A stone actually breathes as it holds and releases water from the air or rain.  Iron fittings were used to anchor stone together but it was not a good idea because in a stone that might be damp, iron can rust and expand.  If it does it can crack the stone.  Wood like iron also expands when it absorbs water.  In fact in ancient times wood wedges were driven into cracks then wetted so that they would swell and crack open the stone. 

Sea shells because they are calcium like limestone seemed to be a logical way to fix stone.  Lead was sometimes used by being poured into prepared spaces in a molten state and then left to cool, anchoring the stone.

Orderly Storing of tools

A craftsman likes to store the tools in an orderly way because it is a pleasure to look at them. Tools do sometimes seem to have a talismanic or fetishistic aspect.  Beyond aesthetic pleasure or psychological thrill, there are solid advantages to orderly tools.  To be able to quickly find a working tool in a moment of need is the only way to estimate how long a job will take.  Time spent looking for misplaced tools is really misspent.  Tools in clean working order can lead to speedy application and predictable results.

Splitting 

‘Rift’ and ‘Grain’ are the easiest and second easiest directions in which to ‘part’  (i.e. split) stone.  In most granite deposits one is vertical, or nearly so, and the other is horizontal or nearly so. Rift is parallel to the mica plates and is the direction of predominant feldspar cleavage. The direction at right angles to the rift and grain is called the ‘hardway’ for obvious reasons.   It splits with great difficulty so the term is exactly descriptive.

Stone that is not split with approximately equal mass on either side of the intended split is likely to curve out at the bottom rather than splitting straight through the stone.

The introduction of saws increased the production of stone for tiling, cladding, and other veneer-type uses, but it uses a different approach to get there. A saw is basically a tool of abrasion.  It can ignore the natural vulnerabilities of the stone. Some stone work still relies predominantly on splitting for its production, slate for instance.


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