"Necromancy" by Clark Ashton Smith

My heart is made a necromancer's glass,
Where homeless forms and exile phantoms teem,
Where faces of forgotten sorrows gleam
And dead despairs archaic peer and pass:
Grey longings of some weary heart that was
Possess me, and the multiple, supreme,
Unwildered hope and star-emblazoned dream
Of questing armies. . . Ancient queen and lass,
Risen vampire-like from out the wormy mould,
Deep in the magic mirror of my heart
Behold their perished beauty, and depart.
And now, from black aphelions far and cold,
Swimming in deathly light on charnel skies,
The enormous ghosts of bygone worlds arise.

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I'm unclear on the first line what "glass" is supposed to mean. There are many options: the thing you drink from, though that seems extremely unlikely; a mirror, which is certainly possible; an hourglass, but not here; binoculars or spy glass, but probably not; barometer, but that doesn't feel right here; vision correcting device, but definitely no. So I guess the most likely thing is a mirror.

Unless... the object of the poem is, in fact, dead, and 'glass' here means gem or jewel to contain whatever spirit or essence the necromancer uses to reanimate the corpse. That's a nasty thought, but seems like it could be a possibility.

aphelion: the point in an orbit which it is furthest from the sun

The picture used is "necromancer" by Alissandra, used here under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported license (https://creativecommons.org/licenses/by-nc-nd/3.0/).

To follow along: http://www.eldritchdark.com/writings/poetry/362/necromancy