Viscosity and density of high-pressure melts can be measured in-situ using the sink float method and neutron tomography. In this method a sample is implanted with objects, such platinum spheres, that have different density and neutron scattering properties compared to the material surrounding them, and the path of the object is tracked as it sinks, or floats, through the melt. Two objects with contrasting buoyancy can be used simultaneously to calculate the density. Pressure, like temperature, is a basic thermodynamic parameter that influences the molecular structure, and thus the electrical, magnetic, thermal, optical and mechanical properties of materials. Devices like the multi-anvil apparatus allow us to observe the effect of high pressure on material structure and properties. Multi-anvil presses are occasionally used in industry to produce minerals of exceptional purity, size and quality, especially high-pressure high-temperature (HPHT) synthetic diamonds and c-Boron-Nitride. However, multi-anvils are high cost devices, and are very adaptable, so they more often used as scientific instruments. Multi-anvils have three main scientific uses: 1) to synthesize novel high-pressure material; 2) to change the phases of a material; 3) to examine the properties of materials at high pressures. In materials science this includes the synthesis of novel or useful materials with potential mechanical or electronic applications, such as high-pressure super conductors or ultra-hard substances. Geologists are primarily concerned with reproducing the conditions and materials found in the deep earth, to study geological processes that cannot be directly observed. Minerals or rocks are synthesized to find what conditions are responsible for different mineral phases and textures citation needed). Geoscientists also use multi-anvils to measure the kinetics of reactions, density, viscosity, compressibility, ionic diffusivity and thermal conductivity of rock under extreme conditions . Figure 1: http://www.ucl.ac.uk/EarthSci/people/lidunka/GEOL2014/Geophysics7%20-%20Deep%20Earth/Earth%20Structure.htm  Figure 2: Earth science: probing the core's light elements Thomas S. Duffy Nature 479, 480–481 (24 November 2011) doi:10.1038/479480a