: On other possible explanation could be the state of the sizing applied to the
: cloth. The sizing effects how well the cloth wets out. If the sizing is
: damaged do to age or handling, the cloth may not wet out as well. I
: suspect your index of refraction is probably true, but it may not be the
: only reason for different results.

Nick,

The sizing certainly is one possible reason for the different appearance. But the wet out occurred without any indication that it was compromised (up close and in person). No lingering white strands in the middle of yarns, no odd appearance, no thick resin... So, it seems to me that any contribution from the sizing would be to the bond state at the interface, not to incomplete wet out. Since the glass/sizing/epoxy interface may be considered a third phase involving various chemical bonds, it would likely have optical properties distinct from the other two phases, glass and epoxy. (Perhaps you are lumping those sorts of details into the heading of wet out?)

Although I have yet to see confirmation, I suspect the sizing used on the S glass is the same as that used on the E glass. So the third phase formed in the S glass and the E glass would be the same - unless of course one had aged to a different condition than the other. If changes in the bond state (third phase) with sizing age caused the appearance of the S glass panel, then we would occasionally see the same effect in E glass. But I've never seen this strong of a "ghosting" effect in E glass. Sure there is always some ghosting with E, especially for the heavier open weaves, but not this strong.

I think Ryan was looking for more direct feedback on his post, so I hope he isn't too put-off by this attention to minutia.

Thanks,
Sam