Moiré patterns are an optical phenomenon that may appear as a wavy, rippled or circular pattern under certain lighting conditions. Moiré patterns may be created when one semitransparent object with a repetitive pattern is placed over another and the two are not aligned.
Moiré patterns are not defects in the glass or silk-screen pattern—they are a pattern in the image formed by the human eye. This may occur when silk-screen patterns of lines or dots are closely spaced and a secondary pattern is created by the shadow of the ceramic frit on another surface of an insulating glass unit, for instance, when a spandrel panel is installed behind silk-screened glass.
Another potential moiré pattern may be the result of light transmitted through the glass portion not covered with ceramic frit.