The exfoliation of two dimensional (2D) oxides, established on the surface of specific liquid metals, has recently been introduced. One such liquid metal is molten tin, which forms a variety of surface 2D oxides. However, the development behaviour of these surface tin oxides is still unknown. Here the evolution of stoichiometry and thickness from single-layer SnO to highly oxidised multi-layer SnO2 in ambient oxygen is explored.