A process for producing a diamond substance with a first inner nozzle and a second outer nozzle. In the first step of the process, a first mixture comprised of oxygen and a hydrocarbon gas is formed in the first inner nozzle; such hydrocarbon gas contains from about 1.01 to about 1.1 moles of carbon for each mole of oxygen present in such first mixture, and said first mixture contains at least about 10 volume percent of hydrocarbon gas. In the second step of the process, the first mixture is ignited to produce a flame core. In the third step of the process, a second mixture comprised of hydrogen and oxygen is formed in the outer nozzle; the second mixture is comprised of at least 2 moles of said hydrogen for each mole of said oxygen present in the second mixture; hydrogen gas and oxygen gas comprise at least about 20 molar volume percent of the second mixture; and the second mixture contains up to about 5 volume percent of hydrocarbon gas. In the fourth step of the process, the second mixture is ignited to produce a flame sheath. The flame sheath is disposed around the flame core so that the flame sheath completely surrounds said flame core and completely shields said flame core from the ambient atmosphere, thereby-producing a composite flame; and the composite claim is contacted with a substrate.