Floors can be pre-finished at the factory or finished on site after they've been installed.
Going the pre-finished route spares you from a few days of irritating dust and fumes. But the wood options are fewer, so you may not be able to match new floors exactly to existing ones or coordinate color with other decorative elements, such as molding and trim. Whether finished on site or done at the factory, the process involves multiple steps.
After boards are sanded, they are often treated with a stain, which can range from clear to ebony (flooring professionals can also combine more than one stain to create a custom color or add gloss to increase its shine). Keep in mind that darker floors, while striking, show scratches and dust more than lighter ones. Alternatively, you can forgo the stain, preserving the wood's natural color.
Stained or not, boards should always receive a few protective topcoats. The main options are oil-based urethane, which has an amber tint and takes about eight hours to dry, and water-based urethane, which stays clear and dries in two to three hours.
Wax is also used and develops a distinctive patina, though it must be buffed and reapplied far more regularly than urethane.