AtD translation: the umbra of brushed hair and skull-heft

[Mike Jing]

P127.11-17   When required she could pose with the noblest here against the
luminous iceblink, as if leaning anxiously out of some portrait-frame, eyes
asking not for help but understanding, cords of her neck edged in titanium
white, a three-quarters view from behind, showing the face only just
crescent, the umbra of brushed hair and skull-heft, the brass shadow
amiably turned toward an open shelf of books with no glass cover there
arranged to throw back images of a face, only this dorsal finality.

What is "skull-heft" exactly?

Also, does the "umbra" and "brass shadow" suggest a lunar eclipse?
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