It is shown by X-ray point analyses and line scans that the concentrations of sodium and potassium, as crown ether complexes, in epoxy resin may not be of uniform distribution. The concentrations may be substantially higher in a thin layer at the base of the block. It is recommended that chemical analysis of a selected central region of a block, not the intact block, be carried out to establish the true concentration. This may be substantially lower than the nominal concentration. This problem appears to be less acute with cryptate complexes of sodium and potassium but a similar trend is nevertheless apparent.