Collyweston stone slate is a traditionalroofing material found in east-centralEngland, primarily inNorthamptonshire,Cambridgeshire,Lincolnshire, andRutland.[1]
It is not a properslate but alimestone found in narrowbeds. It is considerably heavier than true slate.
Geologically, the Collyweston slate forms part of the Lower Lincolnshire Limestone Member of theLincolnshire Limestone Formation, part of theInferior Oolite Group, dating to theBajocian age of theMiddle Jurassic, around 170 million years ago.[2]
The slates are quarried near the village ofCollyweston in Northamptonshire, nearStamford and close to the borders of Lincolnshire and Rutland. Traditionally the mined stone was left outside for three winters until the frost revealed layers that could be broken ("clived") into flat slates.
In the late 1990s,English Heritage (now Historic England) worked with theBurghley Estate andSheffield Hallam University to develop an artificial system to reproduce thefreeze-thaw cycle needed for production of slates. In 2012, when new slates were needed to reroof parts ofApethorpe Palace, further testing was commissioned by English Heritage to develop the artificial frosting and new Collyweston slates have been produced. New slates have been used to repair the roofs ofUfford Church in Cambridgeshire andHigh Wycombe Guildhall.[3]
In 2015 a planning application to reopen a slate mine in Collyweston was approved; the slate mines had not been used since the 1960s.[4] Slate from the mine has been used to repair Bodley's Court inKing's College, Cambridge,[5]Clare College, Cambridge andOld Westbury Gardens inLong Island inNew York.[6]
