Cast iron
In the fence world, cast iron is often used for decorative castings like fleur de lis spikes.
Cast iron is not the ideal material for fence components, because it is very brittle and breaks easily. But it does work well for ornamental features.
One of the main benefit to using cast iron to manufacture decorative elements for fencing is that it's a relatively fast and cheap process, which lowers the cost to create ornate fences using this type of embellishment.