I have passed one Art test. I just made a carpentry blade and was told that "Your Artistic touch enhanced the quality 5127 blade by 100 points." So it looks like that's the bonus for passing Art tests. Perhaps 100 points per test? -Aidenna
The bonus to Carp Blades, Axes, Shovels, and other Anvil items depends on the quality of the item crafted. The closer it is to perfect, the smaller the increase. --Ping
Also, it does increase the more Art Tests you pass. Ratio unknown right now. but I'm increasing 6k carp blades by about 170 points. --Ping