Trapping, Plating, Trimming, and Printing: Let’s Talk Offset Printing.

Design, Printing

I want to talk about something that people in nearly every business will run across from time to time but might know nothing about, Offset Printing. Anytime anyone is looking to print a large amount of one thing, from event coordinators printing invitations to corporate communicators making annual reports, it pays to know some details on how the deed gets done. Think of it think way, if you know nothing about fixing cars and your mechanic says you need new spark plugs and wants to charge you $500 to do it, you might not question the cost and never know your being taxed for your lack of know-how. This article will help demystify some of the dark arts of offset printing and might give you a leg up if you have to haggle print costs. 

Nuts & Bolts: What is Offset Printing?

99% of all print jobs are going to be done one of two ways: Digital or Offset. Both use CMYK colors to make all of the images. You are probably familiar with digital printing without even knowing it. Copy machines and office printers are classified as “Digital” printers. Digital printers use a very similar process, but use rollers or drums to get the ink on the page. Having Office Depot or Staples print off 50 band fliers, that’s gonna fall under digital. 
Offset printing uses metal plates that act as screens and apply the ink to the paper, one metal plate for each color. They are placed in order on a press then the paper is ran through on a spool, inked with each color and then cut to fit the finished size. The set up to run one print job takes considerably more time as opposed to digital. Think about the jobs you send to your network printer: a picture of your niece, a menu to that Chinese take-out place (the good one with the dumplings, not that other one), a meme that you are going to post on your cubical wall. Now imagine that each one of those would require four metal plates, lined up perfectly to make the printout, and then inked up. Digital printers can do that in a minute vs Offset would take hours to get one dialed in just right. 

When It’s Worth It: What is the magic number?

So if Digital printers are so much more versatile, why do things the hard way? Digital printers internally set up each job individually, even if it’s the same page being printed each time, they have ways to speed it up a bit and preferences saved, but it is still doing one piece of paper at a time. Offset is optimized to do one thing well, and that is to make one thing over and over, fast. What is the magic number? 2,000 copies. That is when the tables turn, and Offset starts to be a better value. The trick is, the more you print the better that value gets per piece because at that point you are nearly only paying for the paper you are printing on. An Offset press can also run much quicker than a digital printer once the job is running. 

Jargon: Print Speak.

Here are some terms you might hear getting thrown around when ordering a large offset print job. While most of them might not apply to every job, it will help you haggle if you know what you might not need.

Sheet Fed and Web. Sheet Fed means that each piece of paper is printed one at a time, pulling each sheet like your copy machine or home printer does. This is typically used for smaller jobs and they print what they need and no more. Web press is a much larger press that can print lots of jobs at once from one huge roll of paper that isn’t in sheets, the jobs get cut out of the sheet later. Some things to note, web press sometimes do “gang runs” of several smaller jobs at once. Imagine this as a puzzle where the press techs are trying to fit the most amount of dinner plates on a table. The end process means plating a bunch of odd shaped print jobs in a group and running the press to meet the quantity of the largest job on the press. This could be a bonus for you if you are hoping for any overages on your print job. I have had gang run jobs coming back with double what I asked for with no increase in the quoted price. 

Plating. This is the term you are most likely to hear from a printer because it is where the cost usually comes from. Plating is making the individual four color plates that will put the color on the paper. Think of each plate as a stamp that puts down the color. There will be four of them for the average CMYK job and if there is a change to what you want to be printed at the last minute that means they will have to remake all four plate. TIP! You are printing an invitation to an event and your printer already has made the plate and is printing later today when you get a call that one of your speakers can’t make it. Crap. The good news is If you are making a minor type change to text that is set up as black ink only (which it should be anyway) and if the text is in white space (i.e. doesn’t run over any pictures or other printed color), then they will only need to change one plate, the black one. 

Trapping. Sometimes called “Knock Out” as well. This one is more inside baseball than the rest, I know plenty of designers who don’t know what this means. Trapping is when you make sure the things on the page that you are printing don’t overlap in the final print set up. That large orange circle that acts as a background is a vital design element to the invitation, but so is the photo and text that go over the top of it. Trapping means that when they print, each object only takes up the space that is shown in the final product. 

Bleed. A bleed is any time you print beyond the dimensions of the final product and then trim it back to not have a border of white space on a final product. Bleeds cost more because it adds several additional steps to a print job and a lot of paper waste as well. 

Trimming. Pretty self-explanatory but can be costly so watch out for unnecessary trimming. If you have a print job with no-bleeds and it is running on a sheet fed press, then you shouldn’t need to trim at all. 

Color Bars. These are blocks of color that help the printers monitor ink levels to make sure that levels are not running low. They can check the dots to see if there are changes in the tone. 

Crop Marks. Lines that mark the edge of a document, most commonly used for print jobs with bleeds, but if the job is running on a web press they will need them regardless of bleed or not. 

Registration. The lining up of all of the four colors. A registration mark (looks a bit like a bullseye) is printed with all four colors, along with bars of each individual color, on jobs with a bleed. If the registration gets out of line then the registration mark will start to look blurry, with a halo of the color that is moving slightly. Jobs that come out looking blurry had poor registration. 

Binding. If you are printing anything that folds, from a multi-page book to a card, then you will have to pay for binding. Even a simple fold over card would require a score and a fold, both of those steps take time and precision to set up. 

Score. When the printer makes a mark or crease so that when the final fold happens the paper does so nice and clean. 

Web Break: Means the web press is down while they fix something, usually a paper feed or a roller somewhere started making the worlds biggest spitball out of your job. As in “We had a web break and the press is down for an hour while we clean up.”

Burn a Plate. This means making a plate, not destroying a plate. As in “the client decided they like cornflower blue better than the orange background so we have to burn all new plates.” 

Plate Wear Out. Even the metal plates will wear out after hundreds of thousands of prints, during those very long runs the printer will have to make back up plates. 

Work and Turn. When printing a two-sided job the printer will sometimes set up the press to double the size of the paper, printing the front on the right side and the back on the left for the front. Once the job is done they flip the paper and do the same on the back, knocking out two pieces at a time.

4 over 4, 4 over 1, 1 over 1, etc. These are color terms. If you are printing a postcard that has a full-color image on the front, but only black text on the back, that is a 4 over 1 (as in there are four colors on the front and one color on the back). A flier that has full-color images on the front and back would be a 4 over 4 (four colors on the front and four colors on the back). 

Matte, Satin, Gloss. Just like paints, printing can have finishes. Gloss would be your shiny, high-sheen finish, Satin would have a slight sheen, and Matte is flat with no sheen. I usually recommend Satin as it evens out the texture and discourages smudging. 


Spot Color

color, Design, Printing

Spot colors can be a super useful tool, especially as a cost saving device for the customer. So what are they? Think of spot color as the paint section of a hardware store, all of those tiny custom cards of various shades of hundreds of blues and oranges. A spot color is ONE of those colors that requires no blend, the ink is just that color. Now think of the standard CMYK printing method, you can get close to those colors on the cards, but not quite. Another way to think of it is that standard CMYK printing is printing with 4 spot colors, Cyan, Magenta, Yellow and Black.

Printing in spot colors can save money because you are only using one ink to achieve the color (not a mix of 4) and can cut down on run time and supplies. Note, short runs, like less than 1,000, aren’t going save you money because offset printing can’t beat digital printing for shorter print runs. Some smaller print shops only run two colors at a time on small machines, so a regular 4 color job can double the press time. Also, if your client is looking for something florescent, metallic, neon, or even glow in the dark, spot colors are your only option.

A lot of brands will already have their spot colors defined for you, the YMCA comes to mind, they have the spot color name, the CYMK, RGB and Hex color formulas.  But for this thought experiment, let’s say that a small brand comes to you and they have a bright orange and black color scheme. They are printing a flier and want to keep the cost low, but also want it brand recognizable. You can offer to print the job in 2 spot colors that are already part of the brand itself. You can set up all of the elements with Black and Orange, even complicated images like photos. I’ll show you how.

Picking the Spot Color.

If you are in the USA, Pantone dominates the spot color industry. Investing in a Pantone book is not a bad idea, but they are pricey. Up to date books can run you around $300. The book is important though, because even the website can only show you what the color looks like as a digital image, and depending on your screen settings, you are only looking at a representation that will look different in print. If you have a Pantone book, find the corresponding color and make sure the customer signs off on it. Lets say they decide on PMS 165 C, and PMS Black.

You have your color codes, now how do you design around this?
In all of the Adobe programs, color books are preloaded and you just have to make sure your color is selected when you define what colors are what. Set them as new swatches and build all of the text and elements in those two colors. The tricky thing is converting all of your photos into those tow colors or Duotone. In Photoshop, open up the image you’ll be placing in the document. In the image tab under Mode, you’ll see Duotone grayed out, you have to first convert the image to Greyscale. After you convert it to grey you can select Duotone and a menu will pop up for you to select your colors. Now your photo is a composite of those two inks and will print as a mix, blending with the rest of the two color set up.

You can place that image file into your InDesign doc and finish the layout. You are ready to export your pdf, but how do you export it so that only the printer gets the right file? Export the pdf but turn the color conversion to NONE. Then you can even check your pdf to be sure by doing a fake printing. Set the printer to Adobe PDF and click on “Advanced.” Change the color from “Composite” to “Separations” and you’ll be able to preview what each color plate would look like. Turn off the CMYK selections and view each spot color individually for a small preview to make sure it’s set up correctly.



What is the difference? RGB stands for Red Green and Blue, CMYK stands for Cyan, Magenta, Yellow, and Key (Black). Here is the skinny on both of them.


RGB makes all colors with a mix of those three (red, green, blue). It is an additive color model, which really means if you add all of them together you get white, not black. This is because it is the color mode of items that emit color, not reflect it, i.e. screens. That is why RGB is the preferred color mode for digital design.


CMYK does much the same, but with pigment. You see the colors because the pigment is not emitting light but reflecting it. It is a subtractive color model, which means when you mix all the colors they get darker, not lighter.

Because of those factors, CMYK is the preferred color set up for print. Both offset and digital printers use CMYK. Offset printers use screens, one for each color, that determines where the pigment goes on the paper. The K for Key may sound strange for black, but it serves a dual purpose.

The obvious one is that if it was CMYB some people would think the B might stand for Blue. The other reason has to do with the printing method; press techs would use the black color plate to line up the other colors since the black plate was usually the easiest to see the outlines on, therefore that plate was “Key.”

If you have ever uploaded an image to a website only to be surprised that the reds suddenly were glowing like a Christmas light and the blues were now a bright purple, you probably had the color mode set to CMYK when you saved it. Web browsers aren’t very good at decoding color, and end up interpreting them in wild, unpredictable ways. Same can be said for printing pictures that are set up as RGB.

RGB can display more colors than CMYK, even though there are only three colors, the value associated with each color goes from 0 up to 255. That is a total of over sixteen and a half million colors. That said, CMYK will always print better. There are limitations to what CMYK can produce, and you should prepare clients for those limitations; four colors can only produce so many variations and will fall short when you hit the neon end of the spectrum. I find that a little explanation and education set most clients at ease.