The sets of samples were lifted from the refractories using self-adhesive polymer foam (Technical Foam Services, Corby, Northants, foam grade TFS503 + 4210 SAB adhesive, Fig. ) so that the flat faces of the calcined discs were stuck to the foam. They were then surrounded by a 3D printed PLA frame which was partially filled with epoxy resin to embed the discs (Fig. ). The frame ensures that the top face of the discs will sit parallel to the table in the X ray diffractometer without requiring that the two faces of the cast epoxy be parallel or that the casting is done on a precisely level table (Fig S5). The one problem we have faced with this system is that the asymmetric filling of the frames can lead to bending as the resin completes its curing. Two solutions to this problem were identified. Curved blocks could be straightened by putting them on a flat metal plate and under a metal weight (> 500 g) in an oven at 125 °C for 1 hour and then cooling with the plate and weight still in place. To avoid having to do this extra step, the hardener to resin ratio was reduced from 0.5:1 to 0.27:1 and the bowing of the frames was reduced to within 0.05 mm of flat (Fig. ). Further details are given in the Supplementary Information.