Unfortunately, we live in a time where supply chain issues are causing painful disruptions for the printing industry. Probably at the top of the list of raw materials affected by this is paper. Lead times continue to be inordinately long, and printers and their customers are often forced to use an alternate paper if they want to get the printed product out to the market. But doing so doesn’t come without its challenges.

There are myriad potential consequences of running an alternate paper. The paper may not run as well through printing and finishing devices. It also may not print as well, yielding a product that fails to meet customers’ visual expectations. For one-off jobs that do not repeat, this may not be as much of an issue. But for repeat jobs, or elements such as corporate brand colors, there can be significant challenges with achieving and maintaining the target color.

It’s well understood how much influence the paper (or substrate) can have on the final printed result. Therefore, you need to understand the physical and optical properties of the alternative paper before you go to press and end up with an unfortunate surprise.

Part of any good incoming raw materials inspection process should be to rely on the manufacturers or suppliers as much as possible. It’s not your role to check the quality and consistency of the materials you buy. Just as your customers expect you to verify the quality of the printed product you produce, you should expect the same from your suppliers.

In general, you should always look to get some form of documentation attesting to the quality of the incoming product, often called a Certificate of Compliance (CoC) or Certificate of Assurance (CoA). In the documentation, there should be the appropriate product attributes that the supplier monitors for its own quality control.

In the case of paper, while this speaks to consistency, it can also help you compare an alternative paper you have to run due to availability against your usual, or originally desired paper. Some of the key physical and optical properties to look at for paper (depending on your application) are:

Caliper: important for runnability through a device or press.

Stiffness: important for runnability of products that have some form of finishing that requires folding.

Color: important in understanding the paper’s influence on the final color-printed product.

Brightness: important for understanding the optical properties, especially if optical brightening agents (OBAs) are present.

Not many printers have the means, interest, inclination, or frankly, the need to establish a materials testing lab. Again, you should rely on your suppliers to give you the information you need on the product they supply. However, there are some things you can do that don’t require you to set up a special lab and spend lots of money on testing equipment.

Using today’s hand-held spectrophotometers, which every good shop should have, will give you a number of metrics that can be very valuable in comparing and contrasting paper options. They can also help you compensate for the differences. Many of these spectro-based indices are not necessarily traceable to various standards like TAPPI, ASTM, and ISO, but because they are objective (instrument-based), they are repeatable, consistent, and relative.

By relative, I mean that while the actual numbers may not match an expensive laboratory test instrument (for example, a brightness meter), the measured values can be compared between samples (be it the same paper or different papers) in a relative way. Any measurement system, as long as it’s repeatable, consistent, and appropriate for what you’re measuring, can be of value and better than a subjective assessment.

Today’s spectrophotometers — from companies like Konica Minolta, Techkon, and X-Rite, which all make industrial hand-held devices — can be used not only for process control (measuring density, dot gain, etc.), but they contain advanced illumination and features that enable a number of useful functions for evaluating the optical properties of paper, such as:

Colorimetry: quantifying color via the L*a*b* color space. A paper’s “white point” can be accurately captured and used to compensate for color differences between paper. For process color work, profiles can be easily updated utilizing Substrate Corrected Colorimetric Aims (SCCA) so similar color can be achieved on a different paper. Spot color inks can be formulated for the different paper to achieve the same color target.

Whiteness/Yellowness: both indices are a measure of how white the paper is, or the degree to which a sample is shifted from white toward yellow.

OBA Check (or Brightness): useful to understand how much a paper will fluoresce under fluorescent lighting conditions.

Opacity: where samples are measured first over a black backing, then over white (usually self-backing using another sheet of the same paper).

With the information obtained from a supplier’s CoA, or from measurements you take yourself, you’ll be armed with the right data to make informed decisions on potential process adjustments to achieve the desired result for your customer. And given that color is one of the most important aspects of the final piece, be it through curve adjustments or modifications to a press profile, you will be able to achieve the target color with this information. The more you can understand about a substrate before you run it, the better you can prepare, adjust, and engineer a job for success.

Bill Pope is the Vice President, Technical Services, at PRINTING United Alliance.

In these unprecedented and uncertain times, PRINTING United Alliance and NAPCO Media are committed to providing the printing and visual communications industries with the most up-to-date resources on the ongoing COVID-19 situation. The staff is here to help you as we all weather this storm together.

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