Hello victor778, and welcome to the HP Forums, I hope you enjoy your experience.
I see you're having issues printing on art paper. What is the make, size and wieght of paper? Also, what version of the 8600 are you using? If you have any issues finding the product information you can consult this document:
How Do I Find My Model Number or Product Number?
Please let me know the results of your findings. Thank you for posting on the HP Forums!