Printing White Again

I tried printing a new vector image that required white ink. I opened it in Illustrator and changed the 0% CMYK areas to WHITE_INK and re-saved it. I then proceeded to try printing. Everywhere that was specified as WHITE_INK was still being printed as a dropout. I tried everything within the RIP, but still had no luck. It turns out that all the files I had successfully printed before were saved as PDFs. This one was an EPS. Apparently EPS files discard spot colors. Once I saved it as a PDF, everything worked fine.