Fig. \[fig:phasediag\]. (These observations have been presented and briefly discussed before [@unsticking].) In agreement with equilibrium theory [@cptheory] for systems with short-range attraction, we observed an expansion of the fluid-crystal coexistence region upon increasing polymer concentration (diamonds). To the left of this region is a stable fluid phase (triangles) and to the right is the fully crystalline phase (inverted triangles). These observations also agree with previous experiments on similar systems [@cpphaseexpt].

However, samples with very high colloid volume fractions and/or polymer concentrations (filled circles, squares and crosses) failed to crystallize for weeks to months even though equilibrium statistical mechanics predicts either fluid-crystal coexistence or full crystallinity. Samples with high colloid volume fractions and low polymer concentrations (circles in Fig. \[fig:phasediag\]) showed all the characteristics of hard-sphere colloidal glass [@HSNature]. Weeks after homogenization and left undisturbed, sedimentation showed its effect: very thin layers at the top of the samples developed heterogeneous crystals due to the boundary effect of the meniscus and gravity. Samples denoted by squares in Fig. \[fig:phasediag\], with high polymer concentration and moderate colloid volume fraction, showed signs of transient gels. They collapse under gravity after some ‘latency time’ as observed previously in similar systems [@lowPhiCP1; @lowPhiCP2]. However, the 