Someone asked me today, about the opacity levels and what I use. I'd like to share my thoughts on that.
The level of opacity in a channel only really "half" represents the true happenings on press.
For example, Black in spot color (views) in your art file at 100% black no matter if you mark the channel at 5% or 100%.
You could base that black out so much that becomes transparent and shows colors up underneath but I do not recommend that...unless for some cool stuff going on. For general printing, no. No additional basing needed.
These last few years with the conversion to print with spot colors as a requirement in photoshop, typically, I keep my opacity's at 20% when using standard sim process inks and plastisol
When using watercolor inks, I drop that down to 5. You can even use 3 or maybe 0. They show "something on screen even at 0.
As I lay more and more colors over top, I try to represent a stronger look ot the color. Yellow, when printed last in a sequence of 4-6-8 colors, will be more opaque near the end than it will be up front from getting picked up.
Using spot colors and channel opacity is far less accurate than it was using "selected areas" as an option. It used to be that you could set up all of your seps in "selected areas" and your film printers recognized them as printable. Photoshop changed that in version CS3 or 4 I think. so you could now only print spot colors. Why, I don't know but I loved the old "seleceted area" to print films. It allowed you to really use two opacity levels to your advantage. At that time, I was setting up plastisol at 60 for thin inks and 80% for opaque inks. Then, you also toss in the mesh factor. High mesh, less opacity (being 60%). It was more accurate on screen and you could get a better understanding of how the inks would react. More so than you can today anyways. Back then, if you put 5% in your opacity, you would almost not see your separation i preview.
Also, the (on screen) view on these flat screen monitors do not compare to the CRT's for image and color separation purposes.
Try this.
Create a background color of PINK # ff00f6 FILL for the shirt ( in the color box, look under HSB, RGB and for the # box. Fill it with
ff00f6).
Now, add another new channel in "selected area". in the color box, look under HSB, RGB and for the # box. Fill it with this color. 00ff1e
Now, use the gradation tool and drag with 100% solid black to nothing. Drag from corner to corer.
Duplicate that and change it to spot color at 20% opacity. View each one separatly on the background pink garment.
Major difference in ink representation.
Now, duplicate the "selected areas channel with the gradation again and keep it at "selected areas". Change the color to solid black (10%) opacity.
Duplicate that again, but change it to spot color. View those differences against the background pink garment.
Selected areas were far more accurate (not 100% true), but you could get a good representation to how it would or should print on press.
I have not tried to force it, but I don't think that we are able to print to films using the (selected areas) anymore.
When I get my film printer going and a rip, I will be able to look into these things more easily.
I haven't done it for a long time that way, but it might even be more beneficial to do the seps in (selected ares first) and then convert to spot so you can print films. I did it for a while like that becasue I was reluctant to change but it quickly got the best of me and now all I do is spot colors first.
