I am currently working on a research project aimed at explaining hardness variation of glasses with applied load (indentation size effect) and loading time (hardness creep). I am using the Vickers Hardness scale. My question (that hopefully someone here can answer) is what factors and properties of a material affect its hardness? In glasses, there is a correlation between fictive temperature of a glass and hardness, but I'm looking more for atomic scale properties that influence hardness. Any insight would be greatly appreciated.