The asymmetric filling of the frames which is required in this step can lead to bending as the resin completes its curing. In early experiments the bending was evident after 24 hours curing and increased with time. Thirty days after casting, early frames showed up to 0.5mm bend leaving the top surface convex and defeating the aim of presenting a flat sample array to the diffractometer. Two solutions to this problem were identified. Curved blocks could be straightened by putting them on a flat metal plate and under a flat metal weight (> 500g) in an oven at 125C for 1 hour and then cooling with the plate and weight still in place. To avoid having to do this extra step, trials were carried out in which the hardener to resin ratio was varied and the bowing of the frames after the resin had been cured was measured using an engineer's dial gauge. Using Mouldcraft CLR resin, which had a recommended hardener to resin ratio of 0.5:1, the trials covered ratios from 0.2:1 to 0.5:1. The mixture tested at 0.2 :1 hardener / resin ratio remained viscous and tacky, and was not able to be measured. At the standard ratio of 0.5:1 the frame bowed by almost 1mm after 22 days curing but this could be reduced to <0.2mm by using a hardener to resin ratio of 0.3 -0.4.