Others are probably better experts than Mai on this, but what I'm aware of with this is it's a shroud like cloth with a checkered pattern on it and little eyes within the boxes. It's commonly thought of as a window or doorway.
I've seen two of these. One I assume was real. I saw it in Romania in which Irving used it and it was torn from its stand. And apparently somehow it also got to Detroit, unless it was a different more authentic looking one and was used in an incident Manfred was involved in that also involved the Harbinger?.
The other one was an amateurish painting that was in Mai s ghoul's ( Adam the ghoul s ) bedroom and was apparently driving him quite insane.
Manfred and his coven of Tremere have studied it more extensively and would probably be able to supply more information here.
It now appears as if there are two shrouds, or the one can lead to different places. A realm of orange light and sand, which within a big black Malk lives. The other is a room of cubes in the sky, Manfred and Jon Areson have both been there. When the Shroud that leads to sky/ the sky shoud was at one time given to the Tremere Archon.
During From Saint Andrews Hall to the Vault game session the shroud that leads to sand was opened and The Face was thrown in along with a visit from Jenny Olson and Strauss's arm.