Their primary use was to take waste gases away from the gorge. The existing stack stands 18 metres high. Early photographs show that there were two stacks on this site and there may have been a third.
The stack and the annealing furnace alongside it are the best-preserved remains of the tinplate era.
Annealing is a process of heating and cooling to prevent brittleness. Thin sheets of iron were brought from the Rolling Mill, fed into the furnace, reheated and cooled with water. The water would then run out into the river. You can see this outfall under the footbridge.
Steps leading down to the heat-damaged firebox provided access for boys as young as eight. They'd climb down to rake out the ashes. It was dirty - and dangerous - work.