Many of you who visit the forum probably know that I have been on a quest to create replacement disks. I've become convinced that the original disks have a property that are basically the "secret ingredient" required for correct operation. Read my old posts for a more detailed explanation. One possible factor may be the reddish/green hue seen on original working disks. This has been very hard to photograph. I've been unsuccessful many times before but have finally captured it. Below are seven large photos of a disk surface taken at approximately 30x at different angles so you can see the rainbow effect in action. These were taken with an Olympus D510 digital camera and a 10x loupe over the lens.
The next four photos are from a different disk. This is the area of the disk that gets no head contact at all. Notice that the color is all but gone from the area that does get head contact. It stands to reason that the entire disk surface would have looked this way when they were new. Also notice how liquid-looking the rainbow effect is. I believe this is pretty good evidence that a substance was added to the surface after anodizing.