As a rule, PCTE and PETE filters range from opaque in the lower pore density ranges and translucent in the higher pore density ranges. Because most depth filters are fairly thick, they are usually opaque and cannot be made transparent.

When using with a microscope, note that the polycarbonate and polyester have two (2) refractive indices (Birefringent at 1.584 and 1.625). Under the microscope, the pores display outlines (shadows). The 2 indicates polarize transmitted light into two sets of rays at right angles to one another. Using a mounting medium of 1.584 in a combination with polarized light (matching one refractive index) and focusing in polarized light makes the pore outline invisible.

One can also use the Cyto-Clear Slides, which virtually eliminate distracting pore outlines in polycarbonate filters, the shadows from the pores, and ensures clear observation of the specimen. There is no need to dissolve the filter with chloroform, to use pore-clearing solutions, nor to transfer the cells to a slide. All the valuable benefits of the polycarbonate filter are preserved.

The procedure is simpler and requires less time than present protocols. There are only three steps: filtering the specimen, fixing and staining the cells, and mounting the membrane and sample between glass for examination and preservation.