The bricks were made of locally-found clay which was called 'shale' by the people making the,. There has been very little written about this major industry. Call into the library or email
[email protected] and he will point you towards anything which has been written. I think there is a national Brick Society , who would be able to give you technical information. I can probably find you address of Brian Dempsey, who was at Nori all his working life. There must be plenty of former employees who can assist. I will sent you a private message (PM)