In this paper we employ the non-destructive technique of laser scanning confocal microscopy (LSCM) to characterize NaX zeolite membranes synthesized via in situ and secondary growth at temperatures ranging from 70 to 115 degrees C. A suite of new protocols is developed and applied for the first time for more quantitative LSCM analysis of membrane polycrystalfinity. Through rational segmentation of sets of fluorescence and reflectance LSCM images, membrane thickness and surface roughness are quantified and percolating polycrystalline entities are identified. Through subsequent application of novel image calibration techniques, we measure sub-resolution features based upon differences in fluorescence intensity. These techniques, coupled with evaluation of statistical metrics such as porosity, feature autocorrelation, and feature size distribution, enable more quantitative and conclusive rationalization of even subtle differences in permeation performance based upon membrane polycrystallinity. This underscores the viability of LSCM as a powerful tool for quantitative membrane characterization. (c) 2006 Elsevier B.V. All rights reserved.