There's four pages of this thread, so if someone already brought this up I apologize.
My take on arcanima is that the drawing of the spell (literally, making the image and using special enchanted ink) "uses up" the power of the ink and the geometry. Once cast, the spell goes inert.
Could you use your arm as a basis? Sure, but you'd burn the spell as soon as you were done painting it and then you'd be left with just a tattoo (or an inky arm.)
My take on arcanima is that the drawing of the spell (literally, making the image and using special enchanted ink) "uses up" the power of the ink and the geometry. Once cast, the spell goes inert.
Could you use your arm as a basis? Sure, but you'd burn the spell as soon as you were done painting it and then you'd be left with just a tattoo (or an inky arm.)