The bubble diameter evolution and growth time for forced flow boiling events at two natural and one artificial cavity are quantified. One of the natural cavities had depth of 18μm and a circular diameter of 12 μm and the second was smaller than the resolution of the confocal microscope (i.e. <0.25μm). The artificial cavity had diameter 200 μm and depth 975 μm. Even though the ebullition characteristics at the natural sites are similar to reports in the literature, the bubble evolution at the artificial cavity displays significant longer timescale and larger bubble sizes at lift-off. At the artificial cavity, the ebullition cycles are repeatable leading to lower fluctuations of ensemble averaged quantities than for natural cavities. The effect of cavity size on bubble characteristics is quantified. Finally, the results demonstrated that natural nucleation sites with size less than 0.25 μm can initiate boiling with superheat levels much lower than current expectations.