Coopering involved the making of barrels or casks of staves that were bound together by hoops of copper or wood. They were fitted with a head and bottom. The barrels were made of oak and had to be fitted extra tight so that dampness would not seep into the powder when it was stored. Copper nails were used. In the late 1830s, 16,000 barrels of gunpowder were produced each year in Ballincollig. By 1856 there were about 50 coopers and apprentices employed in the mills.