William Clark &amp; SonsWilliam Clark &amp; Sons William Clark & Sons William Clark & Sons is the oldest linen mill in Ireland and the textile company founded in Maghera, County Londonderry in 1736. The main product is a fine linen canvas for the tailoring industry, used is a unique process of beetling - pounding of the fabric to flatten it. In February 2017 a fire destroyed one of the factory buildings, but the production was intact. The Mills power source was from the Knockoneil River which is an artery of the Clady River. References. "Article contains translated text from on the French Wikipedia retrieved on 1 May 2017." William Clark