The invention relates to soluble metal oxides and mixed metal oxides and to solutions comprising metal oxides and mixed metal oxides. The invention further relates to a process for preparing a soluble metal oxide and a soluble mixed metal oxide and additionally relates to a process for modifying the solubility of a soluble metal oxide. The metal oxides, mixed metal oxides and solutions thereof have a number of applications and in particular are suitable for use as catalysts and also as precursors for the formation of metal oxide coatings. The present invention is also suitable for coating medical devices, and can be used for coating drug cocktails to produce sustained release tablets. Similarly, the coatings may be used for the sustained release of pesticides, insecticides, dyes and fragrances. Further uses include the application of the present invention to coat the moving parts of engines and machinery. Furthermore the present invention has application as use as spacer layers in Metal Enhanced Fluorophores (sensing platforms).