This is where the workers produced the metal components for all sorts of machines and equipment used at Gilfach Ddu. It's a very good example of how self-sufficient these workshops were. This, too, is the highest room in the Museum — the height is necessary to house the 9.5 metre-high furnace, the crane and jib.
The first step in producing the various components was carving the patterns for them (see below). These would then be placed on the foundry floor and packed round with special foundry sand. (You can see several patterns, in their moulding boxes, on the foundry floor.) After removing the pattern the sand in the moulding boxes would be sufficiently compacted to receive the molten iron, that would then harden to the shape of the pattern which had been in the box.
Scrap iron, pig iron and cokes were transported to the foundry on small wagons. The layers of iron, alternating with layers of cokes, would be fired in the furnace. When the iron was molten, the clay plug would be pulled out of a hole at the bottom of the furnace. The molten iron would then flow along a chute and into the ladle.
From 1872 to 1966, when the foundry closed temporarily, the crane was used to raise and lower the moulding blocks. It was also used to hold a ladle steady to receive the molten iron from the furnace before moving it to its position above the mould, then pouring the iron. There is a smaller brass smelting furnace to the right of the cupola. This would be used to cast bearings and other such pieces.
These days, the brass furnace can be seen at work at regular intervals. Working in the foundry on casting day could be hard, hot work and the men were allowed to go home early, as soon as they had finished casting. Today the foundry on a casting day is one of the warmest places in the workshops on a winter's morning!