Stratasys J850 Manual page 28

Models can be printed after they are arranged on a virtual build tray in the
GrabCAD Print application. For information about preparing model files for
printing, see the GrabCAD Print
Before beginning to produce models, it is recommended that you check the
current printing quality of the print heads by performing a pattern test (see
"Pattern Test" on page 4-31).
1. Make sure that the build tray in the printer is empty and clean. If not,
remove cured material with the scraper, and clean the tray thoroughly
with a wet cleaning cloth.
2. Make sure that there is sufficient Model and Support material loaded, as
indicated on the printer interface (see the figure on page 4-4). You may
want to replace the cartridges of Model and Support material currently
loaded in the printer to avoid the need for replacing them during printing.
online documentation.