hourglassing

[derekleffew]

Phenomenon of sharkstooth scrim and sometimes other drops where where the center pulls onstage from the top and bottom. Side masking, either standard legs, or hanging legs the same height as the scrim from the same pipe, is usually the remedy.

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From Scrim and Gauze - Theatrical and Stage Fabric - I. Weiss :

Note: When hung without any side support, sharkstooth scrim manifests an hourglass effect that is natural in the weave. If the sides of a scrim drop cannot be masked and are visible to the audience, we recommend supporting them either with shock cord for stationary pieces or side guides for flying pieces.