Magical Items and Practical Magic

The Korosian mages are often the innovators of Korosian society, each in his or her own way. The flamecallers created the kiln and rudimentary forge to aid in the creation of pottery and metalshaping. Alloying is relatively unknown.
Stormcallers are too few and valued for much innovation, but they often aid in irrigation design.
Masons or stonecallers most recently perfect the oilpress to squeeze the tallowtree nut and collect its oil for lights during the wet season. The oilpress is a huge affair with five pillars around a two ton pestle or pressing stone. Each pillar has a rope which hired men pull on to raise the stone. The base of the press is another large stone with a depression and groves leading to spouts. The oil runs through these groves and drips into collection urns. This oil collecting has given rise to fire arrows. While rare and only used in war for fear of destroying a town or caravan's goods, these darts have a tendency to make quick work of their targets. The tallowtree kil burns hot and spreads on impact.

Utility

The pressing stone, a two ton cylindrical slab of granite, has been known to break the pillars holding it. This gives a sense of dread to those who are hired to lift it.

Access & Availability

The oilpress is a fairly common sight, but its production is heavily controlled by the Takulan mages. They fear the economic collapse of releasing it into other kingsoms.

Complexity

While any mason or engineer could fashion an oilpress, the mages have a natural affinity which gives them a benefit to stoneworking. They control most production and so, many believe only the mages can create.

Discovery

A mage named Nirakut once watched a rice field being flooded. He noticed oil on the water's surface and asked the farmers about it. One told him that the oil came from the tallowseeds hidden by vermin. He returned home and experimented with techniques for extracting the oil. He eventually settled on a press and they proceeded from there.