stacked upon one another the connecting points of the polymer strands can be referred to as nucleation sites hence by increasing or decreasing the nucleation sites one can dictate the pore size and porosity pore size determinations are made by the 34 bubble point 34 test which involves surface tension of the material at hand viscosity of the fluid that the capillary is filled with and the capillary diameter almost all specimens of diagnostic significance urine spinal fluid etc contain measurable amounts of protein which will be bound to the cellulosic membrane causing background staining most staining protocols for cellulosic membranes offer modified stains which attempt to minimize this protein staining the more protein that is present the more the membrane will absorb and stain also the more obscured the diagnostic information becomes polycarbonate membranes composition and manufacture are totally different than cellulosic membranes polycarbonate membranes are made by bombarding a thin 10 microns film of polycarbonate material in a nuclear reactor the atomic particles pass through the material and weaken the chemical bonding of the polycarbonate a subsequent etchant bath creates a precise pore whose size can be very accurately controlled as a consequence of how long the material is allowed to stay in the bath unlike cellulosic membranes the exact size of a nuclepore polycarbonate membrane may be physically measured under a scanning electron microscope to assure the proper pore size the.