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Hi. Thanks. I do it by smartphone in an app called Ibis Paint. :)

The original art belongs to a friend, as you can see on the top right of images 2 and 3. The trade art, is that I make a version from his drawing and he makes a version from my drawing.

Cool, I knew about the trade art culture from deviantart. Do you also have an account there?

no, i usually do these art trades on a social network called Amino :)