Long story short, I’m working with another designers file (yuck) but came across something interesting and thought I’d see what the consensus is here…
PMS 193C colour swatch used throughout the ID doc. There are some coloured areas using 193C with the “opacity” set at 80%. I wouldn’t do that. I would set the swatch colour as a “tint” of 80%… is one way better than the other?
There are people here with more practical experience with prepress than me, but I’d use an 80% screen tint as well.
Specifying opacity creates an object with transparency, which the tint doesn’t. Even if there’s nothing behind the transparency, the RIP will still be treating it as transparent (or translucent, I suppose), which is one more unnecessary complication that could make the RIP choke.
They are two different things.
Tint is still a solid color.
An object with an opacity setting is transparent. You can see the crap behind it if you overlay it.
While either will work on a white background, as B said, if you use opacity you create a transparent Pantone Spot color, which Adobe HATES with a passion so large, it breaks their software. If you’ve heard of ‘dreaded white box syndrome’ or ‘visible atomic areas’ or have had all the glyphs drop out of your files on printing, had an image vanish, even had just one letter (all of them, but just one, like all of the letter “t” in a document), all of those are symptoms of having a transparent Pantone Spot color in your document. More fun, the transparent spot can be anywhere in the file. It doesn’t even have to be touching the thing that is affected.
Even better, it doesn’t make the rip choke, you don’t get an error message, it’ll happily print all those mistakes and the only way to catch them is with a proof. Sometimes you can see them if you look at your file in Overprint Preview, but not always, especially a bad font outline interaction. Gotta say that particular stunt I’ve only ever seen with free fonts, usually with bad outline files, although there was an Adobe Caslon floating around that was pretty bad. Might have been a corruption or something.
All of this still happens, BTW. It’s never been fixed by Adobe. They do not believe a spot color should be transparent.
There are workarounds and there are checks we can do, but the first check is to see if there are any spots used and if any of them are transparent.
I shoulda maybe prefaced my rant that I do wide format digital. I have no idea in conventional print what the rip will do when making plates when it encounters transparency instead of a tint. Tints it understands in line screen. Opacity? Someone with more experience there will have to answer.
Arguably if you don’t convert spots to CMYK before sending your work for output to digital print, you deserve a world of pain when it is printed. Granted, dropping random glyphs is an extreme and sneaky version of pain.
Perhaps it’s just old school, but It was drummed into me in my first job (when the only thing close to digital print was a rainbow proof), to check, check and check again for spot colours before sending to the printer. I remember one guy not doing it and the printer output 4 col films and 7 spots for a solely CMYK job! That guy wasn’t all that popular with my boss. Thankfully the printer called to check before making 11 plates!
I guess it is not quite so critical these days with digital output, in terms of making expensive mistakes, so young designers are less ‘on it’, maybe.
If I were using a spot for litho job, I still wouldn’t use any form of opacity value. Again, make I’d make a tint and make sure it’s set to overprint. May look a bit crap on your layout, but when you check with an overprint preview, it will look fine. More importantly, it will look fine when it’s put onto a piece of paper.
If you convert your spots to CMYK, then the rip does not recognize your Pantone colors, it just goes by the numbers, and we all know, from looking at the Bridge just how disasterous that can be. All the machines I use (granted wide format) are all calibrated to recognize Pantone colors in their profiles, by name and number. Remove those and you get what you get. Use the Pantone numbers and you’ll get a really good approximation right out of the gate for about 65-70% of the printable Pantone colors. I can bump that into the high 80s by doing a chart match using certain CMYKOGV machines.
The idea is to understand your output before doing your input. Yeah, one of the fixes is to Convert all Spots to Process, but you might want to let your printer do that conversion in profile rather than just handing them a bunch of CMYK numbers and hoping for the best.
YMMV in conventional print world.
Designers should KNOW not to use opacity for anything other than very specific effects. But since process is not taught in colleges, and most professors wouldn’t know a “screen tint” from their elbow these days, the difference between Opacity and Tint as been incorrectly blurred. Today it’s all about what “looks pretty on my monitor.”
I still get that, you know.
“But this proof doesn’t look anything like my monitor.” (not directed at anyone here, specifically…)
I guess I should have mentioned this is all on a white background so nothing fancy in this case. But yes I’ve totally been gotten by the ‘dreaded white box syndrome’ and got tired of unexpected results so whenever possible I now flatten any images with transparencies in an effort to eliminate printing issues.
I will use pantone spots within docs to keep colours consistent and then do as sprout suggests and convert everything to cmyk assuming all the conversions will also be consistent.
I do remember receiving another file from this particular designer and once she saw the proof mentioned the blue was to “warm” and can we adjust the printer. I sampled her blue and low and behold it had almost 60% magenta. ugh… I’ll continue my vent a bit more by adding that this file in particular had SO many self made spot swatches, cmyk swatches and rgb swatches plus excess data off the artboard, its a wonder it printed at all.
I think designers overall need to use their preflight and separations preview in acrobat more often to check their files. Sending clean files is a lost art. 
Just the concept of even needing to send clean files is a lost art.
I still get art from a designer that tries to call up images from a job we did years ago because the frames still exist off the artboard…