Copy a drawing from the reference image onto a canvas or sheet of watercolor paper. Outline flames with light, loose strokes. Don't try to pencil in every change in color. Instead, define layers of flames. Notice how colors give way to white at the base of the fire where temperatures are the highest.
Squeeze a small amount of paint from each tube in a semi-circle on the palette. Lay out a large blob of white. Fill a jar with rinse solution.
Paint everything in the picture except the flames and any glowing, hot material. A dark background will contrast with the bright flames and coals. Add any cast shadows for a dramatic effect
Paint all the flames and any burning items opaque white. (Leave the paper white if using watercolors.) With palette knife, mix a tiny dab of yellow into a large blob of glazing medium for wash. Paying close attention to the reference image, gradually build up the color with translucent washes of yellow, going from bright white at the base of the fire to bright yellow at the tips of the flames. If needed, add very small touches of transparent purple or blue to white areas only.
Create a bright orange with yellow and red, blending the palette knife. Mix a dab of the orange paint into a large blob of glazing medium. Blend translucent orange washes into the yellow. Define the tips of some flames with a small brush by outlining the flames with pale yellow. Add depth and intensity with deep red-orange behind the lighter flames.
Paint background colors into some outer flames so they will appear more transparent and around any flames that need sharpening or cleaning up. Go back over the flames as necessary with translucent yellow or orange washes.
Brush white into the centers of any burning coals. (Leave them white if using watercolors.) Add intense yellow and orange washes. Paint crisp, black edges as needed.
Paint the coals that are cooling off bright red. Blend black smoothly into the red from the edges for a softer, more three-dimensional effect.
Paint the smoke with white washes tinged with purple. Paying attention to the reference image, vary the opacity of the washes. Add orange and yellow translucent glazes where appropriate to indicate reflections from the fire onto the smoke. (Watercolors: Paint water over the background where smoke is desired, and lift some of the moistened paint with a dry brush.)