Brightness Vs. Whiteness of Printing Paper
When you’re describing printing paper, brightness is not the same as whiteness. Here’s the difference.
The brightness of a paper stock, which is measured on a scale from 0 to 100, refers to the paper’s ability to reflect blue light (light ranges from warm, or yellow, to cool, or blue). Sunlight, which is 5000K light, is a blue-white light. In contrast, warm-white bulbs you can buy in a hardware store are closer to 2700K and have a yellowish cast when compared to sunlight. Blue-white papers tend to look brighter than yellow-white papers.
On the other hand, whiteness refers to the ability of a particular paper stock to reflect all colors of light (not just blue light waves) faithfully. The whiteness of paper is usually referenced through terms such as solar white (a blue-white sheet) vs. cream or natural white (a yellow-white shade). That is, descriptors are usually not numeric (as they are with brightness); rather, the quality of whiteness is usually conveyed with adjectives.
So, again: brightness refers to the amount of light reflected. Brighter papers have numbers like 92 to 98 bright. In contrast, newsprint is closer to 65 bright, and next to a 92 bright press sheet, newsprint looks dingy. Whiteness, on the other hand, refers to the color of light reflected. A blue-white sheet appears crisper and even brighter than a yellow-white sheet.
Both of these terms are similar and easily confused. The best way to understand them is to ask your printer or paper merchant for samples illustrating different levels of brightness and various shades of whiteness.
That said, it’s also useful to see offset-printed or digitally printed samples on a 65 bright sheet vs. a 92 bright sheet, and on a blue-white press sheet (like solar white) vs. a cream or natural (or yellow-white) press sheet.
Subconsciously, our eyes register a blue white sheet as brighter. Since 4-color printing inks are transparent, the overall look of a printed job on a blue-white sheet will be brighter and will "pop" off the page. In contrast, on a cream sheet, human faces might look a little jaundiced due to the yellowish tone. But if your subject matter does not include people, a yellow-white sheet might be more subdued and might give a low-key tone to your printed piece. In fact, if your brochure or book is text-heavy, a warm-white (or yellow-white) paper will be much easier on the the reader’s eyes.
Going back to brightness for a moment, bright sheets are more expensive. You might choose a #1 sheet with a 98 bright rating for an annual report. In contrast, you might choose a #4 or #5 sheet for an automotive parts catalog. For a long catalog with a large press run, the lower brightness of the #4 or #5 sheet (which indicates less bleaching of the paper during its production) might save you a lot of money.
To be more specific, this is what you need to know about the brightness scale.
1. The brightness scale ranges from 0 to 100. Papers also are also referred to as premium, #1, #2, #3, #4, and #5.
2. For the most part, good newsprint, such as "Hi-Brite," will range from approximately 65 to 75 brightness.
3. A blue-white sheet like Finch Fine Ultra Smooth has a brightness of 98. It is also alkaline (on the pH scale), so it will not degrade and become brittle like a cheaper, acidic paper stock.
4. A #4 sheet may have a brightness of approximately 74 to 79.
5. A #5 sheet may have a brightness of approximately 69 to 74.
6. Some #2 press sheets (which will cost less than #1 sheets) will be almost as bright as the #1 sheets (you won’t be able to see the difference).
7. Premium sheets are even better than #1 sheets (brightness, surface formation, coating), but they are more expensive as well.
8. A #4 freesheet is free of lignin, a polymer binding agent in wood that causes paper to yellow and become brittle over time due to its acidity.
9. A #5 groundwood sheet is good for automotive and parts catalogs. It includes mechanically ground (as opposed to chemically broken down) wood pulp, so the acidity of the paper will cause it to degrade. But for a parts catalog that will be regularly replaced, that’s probably not an issue.
10. Premium, #1, and #2 sheets are usually used for sheetfed offset printing.
11. Premium, #1, and #2 sheets usually have a better printing surface and better coating than lower numbered sheets.
12. The #4 and #5 sheets are usually used for web offset or gravure printing. They are thin, less expensive, and opaque (you don’t see printing on the back of the book page when you’re reading the front of the page).
The Takeaway
All of the preceding information can make your head hurt. So here are some simple takeaways.
1. Involve your printer or paper manufacturer early in the process to determine the best paper for your printed product.
2. Don’t overbuy. Consider the importance of the job. (Is it a high-profile promotional piece? Is it a reference product only? Will readers read it and then throw it away immediately?)
3. Consider house stocks. If your printer buys huge amounts of a certain stock for multiple clients, you will benefit from the discount he receives.
4. Ask for printed and unprinted samples. Look closely at memory colors like grass, the sky, and skin tones. Also see how easy it is to read text on your sample sheets.
Conditioning Printing Paper
You might actually think that stacks of wrapped printing paper, or rolls of printing paper, have personalities when you consider what you have to do to prepare the paper to be printed.
Rolls and boxes of printing paper arrive at your printer’s plant wrapped in paper and plastic. They have probably been outside in a hot truck. Or maybe it’s winter, and the paper is too cold. At that point the paper is not ready to use. Both of these conditions make it hard to keep the paper flat during printing and finishing.
Therefore, the paper must first be conditioned, which involves letting it just sit and become acclimated to the temperature and relative humidity of your printer’s plant. This is because paper is composed of fibers that grow or shrink depending on the moisture content of the paper. You might envision a cellulose sponge, also composed of a fiber, albeit a different fiber, which also grows and shrinks depending on its moisture content.
If you don’t carefully condition printing paper prior to use, a number of things might happen. You might see waviness in the middle of the stack of press sheets, or the edges of the press sheets might curl. Both of these (temporary, and remediable) flaws can diminish the "runnability" of the sheets (their ability to go through the press easily, without jams). Depending on the temperature and relative humidity of the paper, printers might cool them, or even put them in a hot room with heaters to warm and shrink the edges of the paper stacks.
The Takeaway
Here are some thoughts:
1. According to one paper website, Kallima Paper, the ideal ambient conditions for preparing paper for your press include relative humidity of between 45 and 55 percent and a temperature of 72 degrees Fahrenheit.
2. Your knowing what is involved with paper conditioning, plus your knowing the potential pitfalls of not taking the time to do this correctly, will make you more understanding of the time your printer needs to prepare your job.
3. Also, it stands to reason that if you order specialty paper, it will be more likely to need this conditioning time, in contrast to the house paper stocks that are already on your printer’s pressroom floor and ready to go.
[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]