The Ultimate Practice Lock is made from Brass. Brass is a great choice for high quality lock cylinders because brass is self-burnishing. As brass keys slide across brass pins thousands and thousands of times, the brass surfaces polish each other instead of grinding away at each other. If locks, pins, and keys were made of iron or steel, repeated use would wear all parts. This happens less with brass.
Brass does have one downside – brass will corrode and loose it’s shine. Fortunately, the solution is easy. The old standard for keeping brass polished to a shine is Brasso brand brass polish and it does work great. But if you want a quick solution to tarnished brass, you can soak your lock in white vinegar for a couple of minutes and the dirt and corrosion will disappear.