In this work we present a psychometric, visual search-based study analyzing the perceptual appearance uniformity of 3D printed materials. A 3D printer's quality, precision, and capacity to produce smooth surfaces directly affects the perceived uniformity of its outputs. This work represents the first steps towards building a perceptual model of uniformity for 3D printing. Such a model will greatly assist in advancing the quality of 3D printers, especially as they become capable of creating complex, spatiallyvarying appearances. We demonstrate the effectiveness of applying visual search to appearance perception problems by analyzing 288 appearance variations formed from the combination of 18 printed surfaces, 8 virtual transformations of those surfaces, and two illumination conditions. The virtual transformations allowed us to explore the impact of bumpiness, glossiness, and spatially-varying color on perceived uniformity. Significant effects were found to be caused by several of these dimensions. Additionally, the measured psychophysical data is a valuable contribution to the general study of the perception of spatially-varying appearances.