I have only painted ONE flat on both sides, because I found only one flat of the subject and found the two sides very interesting to paint ....
I present my painted flat in frames, not on a table, and therefore nobody would ever see the back (painted in black).
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Today two sided flats allow you to choose the side that fits you the best. And if you wish to paint two warriors or knights or horsemen facing and fighting with each other, you have to decide who will be on the left and who on the right side.
And like you, at 77 life is becoming too short to paint a side that nobody will ever look at.... So I paint one side to paint twice more characters in the same time !!!
Mode is changing , many and more flats are one-sided, it makes them also cheaper in engraving/drawing.
We dont paint on canvas on the two sides either ! ....
Note: When I wish to paint and show the two side of the same subject, I buy twice the same figure and paint them both on their opposed side!!!
For example, I painted on the left and the right of the flag bearer two pairs of the same flat ... for framing the serie....