Starting with the hair I apply the first application of oil over the previously completed acrylic sketch. When working from a photo I find that it helps to paint upsidedown, as that forces me to drop my assumptions and only paint actual colors and shapes.
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If you think this is messy, you should see what's behind me.
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Portrait of an Australian.
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Many times I'll just squeeze paint directly onto the canvas.
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The unfinished portrait.
I'll let this dry as much as it will overnight (I paint with quick drying, water based oils) and apply a second application tomorrow.
Now, back to unicorns.