It has been observed that diamond deposition by flat flame chemical vapor deposition is achieved over a very narrow range of reactant composition. We demonstrate that this diamond deposition window is strongly determined by the nature of the substrate material. Furthermore, once a continuous diamond film is formed, the window appears to be independent of the original material. Substrates examined include silicon, glass, titanium, tungsten, nickel, and molybdenum. The dependence of growth rate, morphology, and quality on reactant composition has been quantified using scanning electron microscopy, Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). It was found that the highest quality diamond was grown at conditions where diamond does not nucleate on ultrasonically scratched silicon. Thus, the production of high quality diamond on silicon by combustion synthesis requires different conditions for nucleation and growth.