Grateful- this is another area our boys are similar! We have been dealing with strong perfectionist tendencies, even down to calling himself stupid or actually hitting himself in the head.
I heard somewhere you can get a presentation from Dr. Amend online that talks about rewriting the script in their heads. I will see if I can find it and PM it to you. It was helpful for me to reframe how we were looking at it.
The other thing I suggest that has been huge for encouraging him to push through the "my art sucks" times is to frame it and hang it up on the wall when he's not looking. I framed one for my parents too and they hung it up. The pride overwhelmed the perfection quite easily :-)
