The Production Of Collyweston Stone Slate
The process of producing stone slate is a time-consuming activity, dependent on the weather and requiring great skill. From Roman times to the 17th century, most of the slate used was obtained from outcropping rock or from the by-product of other quarrying activity. An increasing demand led to the excavating of slate using open-cast methods and by 1633 there were open Pits at Collyweston. This was not a wholly satisfactory method, however, as the slate needs to retain sap in order to be split by frost action, so quarrying only takes place during six weeks in December and January.
A second method of extraction was to quarry the slate below ground via tunnels, shafts and adits known as 'fox holes'. Working conditions were cramped, with the workmen having to lie on their sides due to poor headroom. They would pick away at the rock and sand which lay under the stone slate - working the face in this way was called 'foxing'. Columns of ragstone were left to support the ceiling, with pit props being used in later quarries. Occasionally the workman would tap the rock close to his head to check it was safe to progress along the face. When the ceiling was about to collapse, a series of clicks, known as 'talking', would be heard. Ideally, it would be ready to collapse at the end of a days foxing, and the workmen would retreat knocking the supports down as they went. The mass would then fall to the floor, hopefully breaking into easily managed pieces. If the ceiling did not collapse, steel wedges would be driven into it with a 'lions tail' (an iron bar) which would then be used to lever the ceiling away.
The rocks, known as 'logs', were loaded into barrows, or 'shims' and hauled out. It is vital that the stone remains damp so that the freeze-thaw action of the frost will initiate splitting. At the surface, the logs were laid out on a bed of shale, called the 'patch', to allow air underneath. The log would be watered until the initial frost split was visible. In mild winters, when the log had not split, it was pied', that is laid in a pit and covered in wet earth to prevent drying, and brought back up to the surface again for splitting the following winter. Even today, slaters are still reliant on the frost to split the log.
Once the initial splitting had started, the slater 'clives' (splits) the slates with a 'cliving hammer' by tapping them gently around the edges. The aim is to produce the largest possible slate. Once split, the slates are dressed into the various sizes (
see figure) using a dressing hammer which produces the characteristic rough-edged appearance. A nail hole is made at the top of the slate, traditionally with a 'bill and elves' - an old file worked to a point and set on a wooden handle - but more recently drilled. Originally, the slates were held in place with oak pegs hung over the battens. The dressed slates are Then 'parted up', that is, using a slaters rule' to arrange them into groups depending their size and stacked into heaps each of a 'slaters thousand' - 840 slates! The slates are then taken to site and laid in diminishing courses, with the size of the courses reducing towards the top (ridge) of the roof - one of the important characteristics of stone slated roofs. The bottom of the rafters is tilted up, known as 'sprocketting', to make it easier to fix the largest slates and helped throw rainwater away from the walls of the building.