Abstract The determination of the past ancient magnetic field intensity is typically very difficult and error prone. Fresh volcanic glass has been suggested to be an ideal material for obtaining direction and strength of the magnetic field. Domain state bias is generally absent, thermal alteration is normally negligible and, as demonstrated in this study, cooling-rate differences can be corrected for. Major issues remaining include alteration and the origin of the remanence: that is, whether it is a true thermo-, a thermochemical or, for altered samples, a chemical remanence. Hydration, devitrification and perlitization lead to incorrect estimates of the palaeointensity, which are very difficult to recognize as the palaeointensity analysis does not easily expose these biasing effects and points towards ‘reliable’ results. Particular care on sampling and/or volatile measurements are necessary to overcome these drawbacks.

Progress in the understanding of the volumes and viscosities of granitic and related pegmatitic melts generated by experimental studies are reviewed. The results of a series of investigations of the volumes and viscosities of melts derived from a haplogranitic base composition, HPG8, located near the 2 kbar water-saturated minimum melt composition in the albite-orthoclase-silica system are discussed. Melt volumes, obtained using a combination of dilatometric and calorimetric methods at 1 atm and relatively low temperatures yield an internally consistent set of partial molar volumes for 18 components in granitic melts. These partial molar volumes, combined with an estimate for water, allow the estimation of melt densities for granitic and related pegmatitic magmas. Melt viscosities, obtained using a combination of high and low range viscometry techniques, provide a template for the estimation of melt viscosities in more complex natural systems. The parameterisation of the non-Arrhenian temperature-dependence of the viscosity of such melts is presented, together with some structural implications of the variation of melt viscosity with temperature and composition. Outstanding questions related to the PVT equation of state of granitic melts and to the mechanical response to shear stresses are discussed, with an outlook for the experimental solutions to those questions in the next few years.