I don't see it, but that's not unusual, I don't see the "ghost" faces in window panes of "haunted" houses either. But, why would people that believe in those sort of things assume it was an angel, and not the image of one of the victims, attackers, a demon, or something else?
After the attack, salts, oxides and moisture on the steel's surface affected how the girder corroded, said P. Chris Pistorius, a materials scientist at Carnegie Mellon University who is co-director of the Center for Iron and Steelmaking Research. Air circulation around the ruined steel played a role as well.
"Atmospheric corrosion is very sensitive to microclimates," he told NBC News. "It's actually difficult to get even corrosion of such a surface. It's more likely to get a pattern than to get uniform corrosion."
If layers of steel are lying on top of each other, as appears to have been the case with the 9/11 girder, moisture can "wick in different areas and leave all kinds of different patterns," said Thomas Eagar, a professor of materials engineering at the Massachusetts Institute of Technology.