Well I watched the Speed-Painting vids - the Portrait AND the Spider-Man - and I have to say I was astounded.
But what struck me immediately was how many times the artists went over their work with more and more 'layers'.  It seemed to me that they could have achieved in maybe four 'layers' what it took them 2 dozen or more to accomplish the final view.

But then I'm not an artist......

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All the Woes of a World by Jonathan Icknield aka The Bryster

And in my final hours - I would cling rather to the tattooed hand of kindness - than the unblemished hand of hate...