Note that the Orientation Slice is cut precisely to the (100) before the crystal is rotated and cut at either +.25 degrees and toward the flat, or â.25 degrees and away from the flat (as described in Figure 3).
The era was called the Dark Ages also because we don't have a lot of written sources from that time period, especially from the early part of the dark ages (500 to 800 CE).
To some, it refers to the entire period before a serious interest in classical literature and history began to re-emerge in the late Middle Ages -- the 12th-14th centuries or so. http://en.wikipedia.org/wiki/Dark_Ages.