Learning

Perryfield Quarry

The Lions and Unicorns are being carved using Portland Stone, from the Perryfield Quarry on the Isle of Portland, Dorset.

Perryfield Whitbed

Perryfield Whitbed
A popular buff white stone with a medium to fine grained texture. This stone contains shell fragments in the size range 1mm to 5mm, it is known to be a durable building stone and has been used extensively in the United Kingdom, including in the restoration of Westminster Abbey in 1993.

 

It exhibits a low saturation coefficient, good strength and good resistance to salt. Historic use indicates that it is capable of service life well in excess of 60 years providing that exposure conditions are not subject to severe frosts or high concentrations of sulphur dioxide and that good stone detailing methods are employed to give best protection from surface water ingress. It is estimated that the likely weathering rate of this stone would lie between 1mm to 3mm per 100 years in normal exposure conditions.

Perryfield Quarry
Perryfield Quarry

Blocks of stone are extracted using a method known as 'stitch drilling'. A series of 30mm holes are drilled generally 150mm apart along the line required to be split. The stone is then broken along this line using a method known as 'plug and feather', which are wedges driven into metal guides in the hole.

 

Whitbed Stone Blocks
Whitbed Stone Blocks

After selection, the raw block is ‘primary sawn’. This transforms an uncut block into slices and is done with large circular saws that have diamond-tipped blades – cutting one slice at a time.

A block, saw and operator
A block, saw and operator
(gives you an idea of size).

The blocks being cut by the
The blocks being cut by the
diamond-tipped blades

The block is cut into slices called ‘scants’. The thickness of the scant being equal to the course heights of the finished blocks, which in the case of the Beasts were 1.5 metres.

Scant
The Scant

At the secondary saw (at Fairhaven) the other four sides of the scants will be cut to the widths shown on the template drawings.

Printable version Printable  
Last updated: 26 January, 2008