Wavelength

Peak to peak or trough to trough or somewhere in-between makes no difference to the wavelength, but the wavelength makes all the difference to any of the three.  Another piece of plate steel has developed this odd blue patina, similar to the "bubbles" one from a few days ago.  I pulled back a piece of scrap leaned against this piece and was surprised to discover these turquoise waves.  Now, I'm becoming curiouser and curiouser about their origins.