Granite:

Quarrying

Granite is a hard, resistant rock which has widely spaced horizontal and vertical joints. This property enables roughly rectangular large blocks of granite to be quarried. If a series of vertical holes are drilled between joints and filled with a small amount of explosive, a block can be displaced along a horizontal joint without damage.

Originally it took many days to bore a hole by hand. Two men struck a heavy boring rod with sledge hammers, while two more were needed to give the rod a half turn between each blow. Compressed air drilling began in the mid-1870s, using steam power; electric-powered compressed air drills came into use in the 1890s.

Very large loosened blocks of granite were split into smaller pieces by a small charge of gunpowder or by 'plug and feather'. The latter consisted of boring a number of holes in line and inserting therein a series of steel 'plugs' or 'feathers' which, when hammered in, acted as wedges splitting the rock in two.

Stone Dressing

Once a block of granite has been broken down to the appropriate size required, the sides have to be roughly smoothed off before polishing can begin. This process is known as stone dressing. Stone dressing was usually carried out at stone-cutting and polishing works, rather than at the quarry itself.

Originally, rough dressing was done with a blocking hammer or a dressing pick, with puncheons and chisels for finer work. A more efficient dressing tool was the bush hammer, or patent axe.

The dressing process left a relatively smooth surface which could then be polished.

Cutting of granite blocks into slabs was once a laborious process taking months, using an iron saw with sand and water as an abrasive. With the invention of chilled iron shot (smallpellets of iron) and the use of steel saws, the cutting time was reduced to days.

In the 1960s, endless wire loop saws superseded the old frame saws. Diamond tipped circular saws have also been used for many years.

The later sawing processes usually left a surface sufficiently smooth as to require no further polishing before dressing.

Stone Polishing

Dressing of stone left a roughly flat but uneven surface; polishing produced a smooth, or even shiny, surface. For thousands of years the only way to polish stone was to rub one against another, using sand and water as an abrasive.

Polishing machines were introduced in the early nineteenth century. Flat iron rings were turned by hand over a dressed surface, using sand and water as an abrasive. Steam power for turning the iron rings was introduced in 1830s.

In the 1880s the Jenny Lind polishing machine was introduced (the machine so called from its humming noise, which was likened to the Swedish singer of that name). This had a steel ring - shotting ring - which rotated over the dressed stone surface, iron shot and water were used as an abrasive. Finer polishing stages used carborundum then emery.

With modern saws leaving smoother finishes, the shotting process is unnecessary, and carborundum polishing can begin immediately. A modern version of the Jenny Lind, the Seaton polisher, has four small rotating solid carborundum heads and is often fully automatic.

Carving of granite was always a long difficult process, not speeded up till the introduction of compressed air drills with tungsten tipped chisels. Polishing of detailed intricate carvings was carried out by rubbing the surface with a stone using sand as an abrasive. When chilled iron shot came into use, shotting fiddles were used, with emery and tin oxide putting for later polishing stages.