METACOL III
METACOL III is the best firearm coating available and has made all other coatings obsolete. METACOL III is a bonded, solid-film lubricant. Unlike paint, it will never chip, peel, bubble, or crack and is thin enough (.0003" to .0007") to coat the most delicate internal components. When cured, it chemically bonds at the molecular level with the base metal. It is unbelievably tough (the toughest black finish available), impervious to rust, and self-lubricating. It is the ideal coating for modern weapons and can be applied to carbon steel, stainless steel, aluminum, titanium, brass, "pot metal," and some high-temperature plastics (like HK collapsible stocks). METACOL III is available in standard colors - HK-style satin black (most popular), Colt-style dark gray, classic patina - a gray/green/brown; And special colors - NATO green, desert tan, earth brown, and Camouflage patterns - four-color woodland and three-color desert, and urban.
...ARS did an absolute perfect job on my MP-5. The new [METACOL III satin] finish is undetectable from the original. I should know - my brother and I examined every nook and cranny over the entire receiver. Even the sights and three-lug barrel were properly finished.
- Bob Bishop, Machine Gun News/Small Arms Review
The dark gray is a perfect match for Colt-style gray anodizing (AR-15, SP-1, AR-10). Classic Patina results from a special curing process and exactly matches the World War II gray/green/brown color originally caused by long term storage in Cosmoline. This special process has the added advantage of being an even color throughout and hiding areas of different hardness that standard Parkerizing would highlight, such as weld marks. It is super on Garands, M1As, Springfields, M1 Carbines, Israeli FALs, and the like.
Our most famous METACOL III color is satin black. We specially adapted this black coating to match the factory finish on Heckler and Koch rifles, and have earned the honor of being the refinishing center for Heckler and Koch, USA. It is an excellent match for the Uzi, Galil, L1A1 and Belgium FAL factory finishes.
http://www.arizonaresponsesystems.com/finish/pagemetacol.htm
This is from ARS website.