The authors develop a protective transparent coating of aluminum oxide through direct oxidation of aluminum-coated glass. Aluminum coatings are deposited on low-iron glass substrates using a physical deposition method and then oxidized at different temperatures. A uniform nano-porous structure with grain sizes of approximately 30–80 nm is observed. X-ray diffraction, TEM images, and EDX analysis indicate the formation of crystalline γ-Al2O3, Si, and stishovite-SiO2 as a result of interdiffusion. The samples treated at different temperatures have hardness values ranging from 5 to 9 H, which is within the desirable range for industrial scratch-resistant coatings. The optical transmission of around 75–85% at visible wavelengths makes the proposed technique useful for the design of protective transparent coatings.