How to simulate a color on screen without a underbase?

[im_mcguire]

So here is what I am trying to do:

In photoshop, I would like one of my colors to have part with a underbase, and part letting the shirt show through the ink.

I am imitating it right now with a 50% opacity on the selected area, but I am not sure that will represent that the best.

How do you guys do it?

[Colin]

I have needed to use separate layers/Channels to show how it will truly work - or I play with filters - but its usually more precise to make those specific areas - look visually correct.

Example:  Navy over a partial base white.

On the base white it will look MUCH cleaner and brighter.  Off the base white, it looks normal.  Its easiest to use 2 blues to represent what it will look like.

[im_mcguire]

I guess what I am getting after is, once i have the art without the underbase selected, and I start creeping the opacity down, is there a opacity that will best represent the color of the transparency of the ink on the shirt (in this case the black background / shirt color)?  Or is it just a guess?  I just want to show my client what to expect when they receive the shirts.  We are printing all 6 colors (its all I have) on this job, thus us having the get 2 tones of a color with 1 screen.

Attached is a sample of what I am talking about.

The mid tone brown has the underbase, where the darkest brown will just be that PMS color, minus the underbase, and letting the shirt color show through.

[Lizard]

In photoshop what you see is usually what you get if all your settings and dot gain are calibrated.
I assume you have the sep in channels. Your base should be set around 85% and most colors with high translucency set to 5 to 10%. Dot gain setting of 40% at 50% dot is a good starting point. Let me know if you need help with settings.

[Dottonedan]

What Lizard said is pretty accurate. It changes a little depending on mesh and ink type and even sequence.
I'm finding that the Wilflex white we use  is tender. It's got no ooomph even on a 156mesh. Most times for solid spot colors, they print the base 2 times.For sim process, I set my base down at 65% opacity to get a good understanding of what the top will do. Our top white is almost like a waterbase white. LOL.Anything under 20% halftone starts to disappear into the ink below it.   Sucks it right up.

I set my colors at 10% opacity (could get more opaque as you get closer to the end of the sequence), but different ink types DO make a difference.

That darker brown in your image (with no underbase) will darken a tad 10% or so darker, but it's pretty close.