Transparent, durable films of lithium diborate gel can easily be prepared on a variety of substrates from supersaturated aqueous solutions of lithium hydroxide monohydrate and boric acid by spin-coating. The gel to dried gel to glass to crystalline lithium tetraborate (Li2B4O7) transformation has been studied by infrared spectroscopy of thin films cast on potassium bromide windows. Examination by scanning electron microscopy disclosed that distinctly different crystal morphology was associated with a difference in the transformation rate observed between gel and dried gel films. Films of 250 nm to 30 mu m in thickness have been produced.