This book focuses on the experimental determination of the physical properties of silicate melts and magmas close to glass transition. Abundant new data are presented. The same type of measurement is performed on a range of melts to test the effect of composition on physical properties; and a range of different techniques are used to determine the same physical properties to illustrate the relationships between the relaxation of the melt structure and the relaxation of its physical properties. This book is of interest to experimental researchers in the discussion of data obtained from both a materials science and a geoscientific point of view.