Painting flames can seem like a difficult project because of a flame's abstract form and the changes in flame colours. It's important to remember that flames are abstract, so the brush needs to be held loosely, and strokes are made quickly and in curved forms. Keep the colours clean and avoid mixing dark and light colours on the same brush, otherwise you will get muddy colours. Avoid adding white to lighten the flames, but instead use water or paint thinner (depending on the paint medium) to get that transparent colour at the outside of the flame and bottom of the flame.
Select good quality paints in the medium, acrylic, watercolour or oils, you plan to paint in. Think of the colours of flames and fire when choosing your colours. Choose oranges, yellows, reds, but you should also include small amounts of blue, purple and green.
Think of the abstract shape of fire and its slight teardrop shape. Visualise your fire shape before you start to paint. Remember fire does not have a lot of detail. Use a soft 2b or 4b pencil and lightly sketch in your fire. Erase and rework the area until you have the flame shape you want. Your flame painting will be more successful when you have blocked out the flames with simple sketching. This way you will have a painting guide to follow.
Add different orange and red hues to your palette. Add very small dabs of blue, black and green to the opposite side of your palette.
Start painting the flames with a medium-sized rounded-tipped brush. Make your strokes short, loose and fluid. Curve your hand along the lines of the flame. Use different colours and hues within the flames. Dip your brush in water or paint thinner (depending on the medium) and go over the different colours to blend them.
Use a smaller rounded-tipped brush as you reach the edge of your flame. Thin the paint with water or paint thinner (depending on paint medium) toward the outer edge of the flame. This gives a washed-out effect, giving the impression of transparency and light, like that of an actual fire. Give the same transparent effect to the bottom of the flame. Notice how the bottom of the flame is clearer, while the tips have a more intense orange or red colour.
Change to an even smaller fine-tipped brush to paint smaller flames and side embers in reds and yellows. Use another brush dipped in water or paint thinner to fade out the edges of the small flames adding a light effect.
Use a small brush thinned with water or paint thinner and dipped in blue, green or purple to add accents to the inner part of the flame (the hottest part of the flame). Use a soft rounded-tip brush dipped in thinned black paint and paint strokes between the flames to add depth to the painted flames.