Pressure scales and hydrostaticity

Pressure scales are intimately related to the stress conditions of the actual experiments performed at high pressures. In the present article, I describe the effect of non-hydrostaticity on the pressure standard, comparing two X-ray data sets of gold taken with a He-pressure medium. The analysis of the uniaxial stress component clearly indicates different stress conditions in the He-medium in the two experiments. By taking the difference in the stress states into account, the equation of state parameters of gold are better constrained. This suggests the importance of evaluating the uniaxial stress in the pressure standard in any high-pressure experiments performed beyond the hydrostatic limit of the pressure medium.