Corogard

Corogard*—also spelled Corrogard, Coroguard, etc—was required by the Navy on the forward facing edges of inlets, wings, and empennages of some airplanes beginning in the early 1950s. It was a clear epoxy paint that provided an additional degree of erosion and corrosion protection to those surfaces. The Navy specified that it be "aluminized" by the addition of aluminum power.

It is sometimes described as an unpainted surface and it occasionally might have been. However, it was almost always paint, as specified here for the F4H-1:

This is a picture of the Sageburner F4H at the Smithsonian's Silver Hill storage facility. I'm not sure how soon the inlet was covered after the airplane was placed in storage by the Navy.

Since it was a relatively thick coat of clear epoxy mixed with aluminum powder, the perceived color and shininess varied with lighting and length of time since it had been applied. Some knowledgeable observers report it as being close to silver when new but that weathered to a light gray. Another reported shade is close to aluminum lacquer paint. Another description is “semi-gloss medium metallic gray.”

Note the difference in the following two pictures between the leading edges of the wings and vertical fins.

There are very complicated ways to replicate it, but I tend toward just spraying on matte silver.

*3M filed for the wordmark "Corogard" in October 1951 and it was registered a year later. It is described as a "transparent protective coating material applied in liquid form ... said protective coating material drying after application to form a hard, tough transparent film." 3M allowed the trademark to expire in 1993.