A diamond’s fire shows how well it can reflect colored light. The more shine the more it costs, the wider the range of colors it can reflect. If the stone is too shallow or too deep, this will not work as well as you may want it to, no matter how much cleaning you do.
This is the measure of how well the stone reflects light when in motion. A high-scintillation diamond will have fewer dead spots, which are placed inside the stone that do not reflect light at all. Scintillation combines both colored and colorless light, to amazing effect.
Brilliance is how well the diamond reflects any light. This is more obvious in dim lighting when the stone looks brighter from certain angles. Two pieces cut from the same stone can differ in brilliance. This means you need the right cut to ensure light is reflected well.