Within Inkscape I think its not possible, but exporting our svg to Scribus it can be donde. Scribus have prepress nice features. Take a look at: http://wiki.scribus.net/canvas/Pre-Press theres a section for Overpinting and Knockout.

From: "id746-spam@yahoo.co.uk" <id746-spam@yahoo.co.uk>
To: inkscape-user@lists.sourceforge.net
Sent: Wednesday, August 10, 2011 4:20 AM
Subject: [Inkscape-user] Printing separation knockout


I found this thread on a graphic design forum (I edited names out) and I am curious how this specific situation translated for Inkscape users

Cedric Sagne

Thread below

Printing Separations knockout ?
I’m a graphic designer at small printing shop. We have a job with a 2 color logo (which is a black chair with a black pattern on the red upholstery). The press operator has asked that we print black on top of the red field so he doesn’t have to deal with the extra tight registration required in the pattern of the chair.

I created the logo in illustrator with a black pattern on a solid red field but when I send the file as separations the red plate has white where the black lays on top. I’m new at pre-press design so my vocabulary is lacking a bit but I think this is a knockout issue. Does that make since? How do I get it to send as a solid red so we can lay black on top?

reply from k
Select your all of the black elements AI and set them to overprint in the attributes panel (kind of surprised it isn't already, as black usually overprints)

Is it not standard black (ie rich black or a PMS?)
Reply from C
If it's 100% black, a lot of rip softwares (and a lot of design software) will make it overprint automatically. If it's a black spot color (i.e. Pantone Black) it may not automatically overprint, so you may have to tell it to overprint.
Reply from A
If you've used a pattern fill, you may have to "Expand Appearance" on the object and make sure it's solid K. there may be some other colour involved in the default illy pattern fills...

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