Moiré is the enemy of what may have otherwise been an award-winning print. Moiré is any pattern created by an unintended conflict between mesh-weave, digital or analog raster, and garment knit, which is independent of the halftone image.
Inversion moiré is indicative of a screen with corner distortion, usually related to improper clamp placement or incomplete corner softening. The inversion pattern does not exist in the central areas of the image but becomes conspicuous at the edges of a very large image and gets progressively worse near the corner of the frame. Proper clamp placement and proper tensioning will eliminate inversion moiré.
If the corners are excessively tight, inversion moiré is likely to occur in any or all four corners with a large image. Relax the corners if the frame is retensionable. If the stretcher is mechanical or pneumatic, adjust the clamps so the corners are free. If a panel is used, relax the tension 5N/ cm² and compensate with a 1/16" increase in off-contact distance.
Source: Joe Clarke