Tribbe's idea is similar to that proposed by Ian Wilson in his 1978 book The Shroud of Turin: The Burial Cloth of Jesus Christ? -- that is, the Shroud was folded up into eighths and viewed through a grilled window. Wilson's theory is that such a representation led to the Shroud being known as the Image of Edessa.
Tribbe's suggestion is that the term "holy grail" derives from the "sacred face" being viewed through such a screen. Grill = grail.
I was also bemused to find a couple of notes from the author in the copy I picked up at a thrift store.
Well, that's the tale of this book. Track it down and evaluate Tribbe's ideas for yourself! Until then, sorry to get all up in yer grail!
See you Monday.