Asphalt shingle ferrous metal corrosion?

This photo had the name Johnny M. Prater attached to it. I can’t find him and I’m trying to confirm that ferrous metal corrosion is actually what is shown in this photo.
Anyone know him or know anything about this photo or how ferrous metal might get into shingles?

Are those rust stains or a case where water is running down the rain trough and coming in contact with the zinc covered nails. That would clean that portion of the shingle.

The shingles look like a more vivid burnt sienna coloring under each rain trough.

Excellent work Kenneth, thank you! How’d you do that?

Jeff, discoloration seems to be concentrated below keyways (rain troughs), and since the keyways concentrate water, that would support the theory that there is ferrous metal in the shingles. The fasteners should be located at least a half-inch above the tops of the keyways, so I don’t know how fasteners would be getting wet and corroding. I have never seen a photo like this.

Johnny sent a sample to CertainTeed and they diagnosed it.

So was it the upper half of the shingles that had the ferrous metal? Or was it just because there was more water concentration in that area.

Johnny said that CertainTeed said that somehow ferrous metal (metal containing iron) had gotten into the production line at some point. You see more corrosion beneath the keyways because water is more concentrated there. The upper halves of the shingles are not exposed to water since they’re covered by the shingles in the course above, so you wouldn’t see corrosion from there. The corrosion is only where the shingles surface is exposed to water.

At least that’s my understanding. I don’t think CertainTeed was real specific.