Back to Dye Printing Tricks & Tips
It's a tool for proofing your printing project before going to press.
Why have one?
It's cheaper than printing the job, then discovering an error.
Why is it blue?
The yellowish paper is photosensitive. When exposed to UV light, unprotected areas turn blue. (In the olden days, proofs were made that produced images in brown. They were known as Van Dykes, as in Vany Dyke brown.)
Can I use that paper for my print job? It's cool!
It's too slick for the ink, and costs over $700 per box. So no, you don't want to use it for the actual print job.
How come my multi-color piece is just various shades of this blue color?
The various negatives that will be used to actually print your project are each exposed to the same piece of blueline paper. One at a time. The lighter inks that will be used get less exposure time, revealing a lighter blue.
Why isn't it the same as a color proof?
Color proofs can be made from the negatives, but they are far more expensive and time-consuming. Bluelines are cheaper and faster. (The trend is actually going to imaging color proofs to the same matrix as the film or plate creation, but using toner and special paper. Running to an average deskjet or laserprinter isn't actually as accurate.)
What should I look for on a blueline?
Bluelines were originally best for making sure the printer's mechanicals included all the text and graphics you wanted. And to make sure all your photos were correctly scanned and placed into the right position.
Now, with desktop publishing and deskjet proofs provided by the client, bluelines are to make sure no fonts were left off (resulting in Courier instead of your desired typeface), to check multi-page projects are correctly ordered, and that the size you want the job is correctly trimmed.
What should I not be concerned with on a blueline?
Well, it's the worst time to reconsider your content (unless you really want to repay for all new film and a new set of film).
It's also not good for checking ink coverage, color separations, nor exact trapping. Bluelines aren't extremely accurate for paper choice, since the paper used is in no way accurate to what stock will be used on the presses. The texture and thickness also has nothing to do with the final paper stock that will be used.
Okay, how does it work?
Your electronic file is imaged to film. The black area masks the plate from light. Any of the clear areas (shown here in white) will be where the ink will eventually go.
All pieces of film are exposed to UV light on a piece of blueline paper. One at a time (follow the red arrows from the film to the blueline paper). Different exposure times are used to help differentiate between color inks, though it can be hard to tell the darker ink choices from the "black" as all will burn to blue.
Once the blueline is approved, it is kept by the printer for the pressmen's reference.
Then the same film that was used to make a composited blueline will be used to make separate color ink plates (follow the blue arrows from the film to the metal printing plates).
The teal areas are burned onto the plates using the same UV lighting. The plates are cured.
Now the film is filed away.
The plates are put onto the printing press. Ink will adhere to the teal areas, but not to the rest of the plate. The ink is transferred to a rubber blanket, then to the paper stock.
One plate per color of ink (follow the green arrows from the plates to the paper). Notice there's one purple ink plate and one orange plate. Both inks will be put onto one piece of paper, but unlike the blueline, you'll be able to see the difference now.
Since the same film that created the blueline is used to create the plates, all elements seen on the blueline will be printed in a color of ink. (Remember that the pressmen can put any color of ink on the press, so you can swap out the ink colors at the last second--the film doesn't care which ink is used, we just have to be careful that every image, text, photo, graphic, whatever, is correctly imaged to film BEFORE it goes to press. That is what a blueline is best for. Checking.)