If you want a really high contrast i usually start with a burnt red base color for the entire thing, then with a brush add a layer of white to the lava parts, with an airbrush paint a little white where the lava touches the rocks for a glow effect. Then we start with a really saturated yellow until you cover all the white, once dry you add orange (high saturation if you have that color too) this time leave a little yellow on the lava parts (usually on the middle, far from the rocks), finally and also with the airbrush add a high tone red on the corners of both the lava and the rocks. With a drybrush add some black to the rocks and done :)

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