Diagonal cutting pliers are usually coated with a rust inhibitor which lubricates the joint as well as providing resistance to corrosion.
A few models are plated in chromium which helps to prevent corrosion and provides an attractive finish.
The chrome-plating process involves placing parts in a vat, or bath, and using electrical currents to bind thin layers of a metal to the parts. A copper layer is applied first to increase the electrical conductivity of the pliers (how easily electricity can pass through it), then layers of nickel which protect the copper against corrosion and, finally, layers of chromium.
Other models may have titanium coatings on their joints. Titanium is a very corrosion resistant and durable metal, perfect for reinforcing the moving parts of diagonal cutting pliers.
