Examination of the PAS-positive epidermaldermal basement membrane and the basement membranes of eccrine sweat glands by phasecontrast microscopy showed that large segments of these membranes were azure blue in color. This phenomenon has been shown to be characteristic of Schiff-positive material. Some parts of some basement membranes demonstrated an orange or reddish color rather than azure blue. This observation may indicate that the polysaccharide content of all basement membranes, and sometimes even the same basement membrane is not homogenous. Merging of some of the blue material of the epidermal-dermal and sweat gland basement membranes suggests that these two basement membranes may originate from interaction between the epithelium or epidermis and the adjacent stromal connective tissue.
Cawley EP, Wood BT, Weary PE. Examination of Basement Membranes by Phase-Contrast Microscopy. Arch Dermatol. 1968;97(1):78-79. doi:10.1001/archderm.1968.01610070084012