BZP forms colorless, large, light square plates. The plates are very light and are best photographed with a cover slip. The square plates appear a light blue under crossed polars but only when they are suspended in the drop and not in the same plane as the glass slide. Like other tests for piperazines described in other section, this test is very sensitive and can easily overgrow at concentrations of BZP as low as 1 μg.