From the (now defunct) Netbook of Tinkering (which I wrote)
COMPASS
A compass is a small device that contains a magnetized arrow, made of a sliver of metal, which floats in water. This arrow, when used outdoors, away from metallic objects, will always point towards the magnetic north pole. In our world, magnets have existed since the ancient Greeks and Chinese first discovered them in the form of lodestones. The first known compass was probably first developed by the Chinese some 4500 years ago. This earliest compass used a splinter of a lodestone that floated on the surface tension of water. Other early compasses used small lodestones that could be suspended from a string to determine direction.
For a tinker to create a compass, he need only build a container for it, and find a lodestone. That last part is the tricky bit. Lodestones aren't terribly common. A lodestone is actually just a rock that contains high amounts of a material called magnetite. Magnetite can be found in large quantities in volcanic regions or near large iron deposits. Lucky tinkers might be able to purchase lodestones at curio shops where such oddities appeal to rich nobles.
Once constructed, a compass will point to true magnetic north. These compasses are not terribly powerful, however, and any large amount of metal (suits of armor) nearby may skew the results of the compass. These compasses function particularly well in a forest, or outdoor setting.
* The cost of a compass does not include any costs associated to the lodestone. If it is found, it is free, otherwise it is subject to availability.
Components:
Lodestone, glass lid, small round tray, some water
And this is an answer to Zhure's question -
(From the Artificer's Handbook, from a section that I wrote, coming to a store near you soon). The Artificer's Handbook is at the printers currently.
Iolite
Description: Iolite exhibits a property known as pleochroism. This means that the gem has a different color depending on the angle in which you view it. An iolite cube will appear blue to violet in color from one side, clear as water from the other side, and honey yellow from the top. When cut properly it is usually purplish blue.
Lore: Leif Erikson and other Viking explorers used iolite lenses to help them navigate the oceans. Looking through the lenses, they could determine the exact position of the sun, and could navigate successfully using this technique.
Uses: Any color-based spell such as color spray or any of the prismatic spells benefit from iolite. Additionally, divination spells that reveal locations also use iolite.
