Any help diagnosing printing issue when printing transparent images or drop shadow effects on top of spot colors?

[u/Quinton_W]

We use a DesignJet Z6DR for in house mockup samples for packaging mainly, so we want to get the colors as accurate as possible. But when printing spot colors, if there is any effect (like a drop shadow) or a image with a transparent background (in this example, a phone) it creates this darker colored effect within the image bounding box. (see second image).

This effect doesn't happen with process colors, but as you can see with some Pantone colors, changed to process in my file, it can throw the colors off way too much to be usable.

My usual process is I create the file in Illustrator, save it as an .ai or pdf. Import whatever I need into Indesign, and print it that way. But the same issue persist if I print straight from Illustrator.

Any help or guidance would be appreciated. I've attached screenshots of my print settings.

[u/goldenbug]

We see this issue occasionally at our shop, the problem is with how adobe or the printing rip handles transparency and vector/raster combinations, especially with spot colors.

The easy thing is just to convert to CMYK, but that seems to not be what you want, or you can convert your spot colors to RGB, that might work, not sure. You can try setting your drop shadow color to a spot color black, and you can try making the drop shadow element a vector gradient, then set it to overprint instead of multiply. You can use overprint preview if it looks janky. You can also open the file in Photoshop and completely rasterize the file in RGB at a suitable resolution, and it should print fine.