The HP indigo printer can add a "spot varnish" effect via a matte ink. the question is how to tell the printer where to put the effect. I'm thinking a tint swatch aliased to the matte ink but would love to hear from anybody with experience of using the facility, and any tips on designing for use of the "spot varnish" effect on the HP indigo in Indesign.
You got it.. make a PMS color swatch (so it will appear on it's own plate" and call it Spot varnish. Create a new page in the document. Copy and paste everything that is to receive the varnish. Apply the color to everything. Just use solid boxes/shapes for photos, type colored in that color and such. Apply drop shadows in the same color if you are hitting drop shadows.
Feathered edges can sometimes be tricky depending on how the operator runs the varnish, but you can achieve nice results.