One disclosed embodiment concerns an aqueous inorganic coating precursor solution comprising a mixture of water, polynuclear aluminum hydroxide cations, and polyatomic ligands selected from nitrate (NO3−), nitrite (NO2−), or combinations thereof. In certain embodiments, the composition has a molar concentration ratio of polyatomic ligands to aluminum of less than 3; an aluminum cation concentration of from about 0.01 M to about 3.5 M; and/or a polyatomic anion concentration of from about 0.1 to about 2.5 times the aluminum cation concentration. Embodiments of a method for forming the precursor solution also are disclosed. For example, certain embodiments comprise adding a metal having a sufficient reduction potential to reduce nitric acid to an aqueous solution comprising aluminum nitrate (Al(NO3)3).