Pantone and process colour interaction

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Hi, I'm trying to find an answer to a problem I encountered at work today.

The three swatches below have been printed using an older Epson proofer (apologies, I don't have the exact model handy). The pdf I printed from was exported as PDF/X-4:2008. The two swatches at the top were setup in Illustrator where one colour is multiplying (overprinting) the other.

I can't understand why black overprinting PMS 109C results in a colour which is lighter than 100% black. Shouldn't I get a very similar result to when black overprints Process Yellow as seen in the swatch on the right? I wondered whether the proofer might be simulating Trans White in the yellow PMS ink, but as you can see from the other photo PMS 109C has no Trans White in it.

The job I am ultimately trying to create proofs for will be labels printed flexo. So my question is:

Is the proofer giving me an incorrect indication of how black and PMS 109C will overprint one another, or is there a reason the swatch on the left looks so different to the swatch on the right?

Cheers.

 

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Our proofer is an Epson Stylus Pro 7880 which uses CMYK, "light cyan", "vivid light magenta", "light black" and "light light black". The RIP is EFI Colourproof eXpress version 3.5.2.

 

[Stephen Marsh]

Some proofing RIPs “predict” the interaction of process+spot or spot+spot better than others do. Over and above predicting/interpolating an expected colour trap, there may be options to interpolate or reference spectral reflectance data from measured samples. Unless you have measured samples using the exact inks and substrate and print sequence, “proofing” may be a crapshoot.


Stephen Marsh

 

[mastegman]

My guess is that the RIP might be treating the Spot as opaque and not transparent like all process colours. I'm not a flex expert but this could produce the effect shown in your screen capture especially if the black was printed on top of the PMS. My questions is... Why do you want to overprint black onto a spot?

 

[Simon Ivarsson]

Most rips cant predict spot colour overprint correctly.
Not even Illustrator can do that.
Therefore the proof you get wont be correct.
have a look at GMG opencolor