I've often wondered about this, but have never got any real answers. I would presume that each colour differs, as with oil paint.
In your case however you can get a decent preview just my multiplying the black over your Pantone colour, no?
I consulted my printer, he told me something similar: the darker the ink, the less transparent it is.
Meanwhile i did print something with pms 032 c (bright red), and 0% solidity gives me the most realistic preview on screen, compared with the printed result.
For dark pms colors, i shouldn't set the solidity much higher than maybe 20%, as pms inks seem to be very un-opaque (uh what's to oposite of opaque?). Bright pms inks in offset printing should be set to 0% solidity. Hope that helps.
came across this post looking for a good reason there's even an option to set the solidity to anything other than 0.
That setting only affects the appearance on screen. It does nothing to affect how the inks are applied.
For practical purposes, assume all of your inks are translucent. Even process black. If you print a black frame over 4-color art, you'll see the art through it.
Yeah, a particular ink may be opaque, but how much? Yes, that was your original question, but there's no point trying to guesstimate how the inks will interact. You're always better off controlling that with masking.
Long story short, you need to knock any spot ink out of any other ink, unless you want them to mix together. And then you have to trap it.
Yes, there is no way to really know what opacity value to input as a preview.
There is only a solid Lab colour value, there is no TVI/dot gain curve info, nor is there any info on Lab values at different tones, nor is there any opacity info, nor is there any info to show how this may mix with other inks on a given substrate.
Spot colours and their interaction with other spots or process colours is basically guesswork in Adobe apps and in many hard copy inkjet proofing scenarios and most softproofing software.
There is a new ISO standard – 17972. This new standard uses CxF (XML based) information to communicate spot colour information throughout the supply chain (Brand > Design > Prepress > Ink Lab > Print Production). Spectral reﬂectance data and is used instead of colorimetric data. A minimum of 6 patches can be used to capture spot colour behaviour. Ideally only 22 patches are recommended for greater accuracy (not thousands of patches as with traditional ICC profiling).