Four different processes to produce porous MgO have been studied; firstly, calcination of powders at several temperatures before forming by uniaxial pressing; secondly, effect compaction of powders at high mechanical isostatic pressure (400 MPa), followed by sieving and classical forming, addition of dopants, such as Li, Na and Al, and finally, a pressure gas sintering, even after long dwell times at high temperature (1700 °C/24 h). Densification during sintering has been studied. The microstructure evolution during stabilisation test, i.e. 1700 °C up to 24 h has also been characterised. Thermal treatment of the powder does not permit a good dimensional stability of sintered samples, the shrinkage rate after 1 h at 1700 °C is about 0.2% min⁻¹. The addition of shrinkage delaying dopant (Li, Na) is not efficient, Al has a positive role, but depends on the addition process, the shrinkage rate after 1 h at 1700 °C is about 0.002% min⁻¹. The high pressure powder compaction has an intermediate effect (the rate of sintering is about 0.01% min⁻¹). Using a high gas pressure during sintering results in pores with flat surfaces, without re-densification during the 1 h treatment at 1700 °C. Nevertheless, the microstructure shows a grain growth.