Powder coating was invented in the 1950s, and it's one of the fastest growing finishing technologies available. Currently, it represents 10% of all industrial finishing applications on the market.
The powder itself can be either a thermoplastic or thermoset polymer. Thermoplastics do not undergo a chemical change during the curing process, and so can be re-melted and reused if necessary. Thermoset polymers do change chemically in high temperatures, so they cannot be reused once they're applied. However, they tend to be more durable than thermoplastics. The powder can be made of polyester, polyurethane, acrylics, or epoxy.
The coating is applied via electrostatic charge. The dry powder is given a positive charge as it's shot through a special electrostatic gun, and it naturally adheres to the negatively charged, grounded metal piece. An oven heated up to 400 degrees finalizes the coating.
A powder coating's performance depends on the pretreatment of the product, and the powder's resin and pigment. The product should be stripped of any oils, residue, and rust beforehand for a higher quality coating.
This type of finish is great for a multitude of applications, both decorative and protective, consumer or industrial.