THE HISTORIC ENGLAND
COLLYWESTON PROJECT
THE HISTORIC ENGLAND
COLLYWESTON PROJECT
RE-ESTABLISHING PRODUCTION OF COLLYWESTON SLATES
5/10/14
INTRODUCTION
MINING
THE GEOLOGY AND FROSTING OF SLATE LOG
SLATE MAKING
ROOF SLATING
GLOSSARY OF COLLYWESTON STONE SLATER’S TERMS
Clive - setting a frost-split log on edge and gently tapping with a cliving hammer along each edge in turn until splitting is completed.
Dressing - shaping the clived logs to the largest size slate obtainable.
Foxing - the method of mining by removing the sand bed from under log and allowing it to fall.
Frosting - exposing the log to frost to open the laminations.
Heap - quantity of dressed slates of all sizes on the ground made up as follows:
-Case = three slates
-Hundred = forty cases = 120 slates
-Heap = seven hundreds = 840 slates plus thirteen large ones.
Log block of stone of no defined size quarried for the purpose of making slates.
Parting a set of slates of the same length.
Pied method of storing logs during the summer to prevent drying out.
Pit mine or quarry for the extraction of stone for slating.
Square one hundred square feet of slating laid on the roof. A "heap" should produce about two squares of slating.
SLATE SIZES AND NAMES
Lengths in inches
Ridge
Anything under 6” is called an outrule
6” even mope.
6 1/2” large mope
7”even mumford
71/2”large mumford
8”even job
8 1/2”large Job
9”even short‑un
9” 1/2”large short‑un
10”even Iong‑un
10 1/2”large long‑un
11”even shortback
11 1/2”large shortback
12”even middleback
12 1/2”large middleback
13”even longback
13 1/2”large longback
14”batchelor
15”wibbett
16”twelve
17”fourteen
18”sixteen
19”eighteen
20”in‑bow
21”out‑bow
22”short ten
23”middle ten
24”long ten.
Eaves
On a large roof and if suitable slates are available the half‑inch graduations may be continued beyond 13 1/2” with the prefixes 'even' and ‘large’. Slates up to 27" long are sometimes available.
The production and use of Collyweston slate has a very long history. As early as 1286 Cambridge Castle was roofed with ‘slatestone of Peterborough’, referring to the slate shipping point on the river Nene. By the late fourteenth century the trade was well established with 14,000 slates supplied to Rockingham Castle and 5,000 to Oakham Castle.
The production process relied on frosting to clive the log. This involved laying it out in the fields when a frost was anticipated and keeping it wet until it started to split. But during the late twentieth century a period of warm winters led to a decline in production and the loss of many roofs as slate was taken from less important buildings to repair others. For a number of years, log had been available from Bullimore’s aggregate quarry but the continuing frosting difficulties failed to solve the problem with fewer and fewer new slates available. By the beginning of the twenty-first century the situation had become critical and English Heritage (now Historic England) initiated research into how slates could be artificially frosted. This is the story so far.
August 2014
Update 2016
Following the completion of the research Messenger Construction, who managed the project, has continued making slates. Also Claude N Smith roofing contractors has successfully reopened their mine and are now producing slates throughout the year - see last video below.
Completing the story. Mining and frosting at Claude N Smith Collyweston Slaters Link