One paper may have a slightly blue-white appearance, another may appear warmer or cream-colored, while another may have a subtle yellow or gray tint.

These differences are important.

In many paper applications, color is one of the first characteristics noticed by a customer. A slight difference between production batches can affect the visual consistency of books, packaging, labels, stationery or printed products.

For this reason, Color Measurement in Paper is an important part of modern paper manufacturing and quality control.

Instrumental paper color measurement allows manufacturers to convert visual appearance into numerical data. Instead of depending only on subjective descriptions such as “more white,” “slightly yellow” or “a little darker,” laboratories can measure and compare specific color values.

Depending on the application and instrument, paper can be evaluated using parameters such as:

CIELAB Lab*

Color difference

Whiteness

Brightness

Yellowness

Opacity and other optical properties where supported by the appropriate measurement system and method

The result is more objective and repeatable paper quality control.

Why Does Paper Color Matter?

Paper color can influence both the appearance of the paper itself and the appearance of printed content placed on it.

Consider two sheets of white paper from different production batches.

Under ordinary room lighting they may appear almost identical.

Place them next to each other under controlled conditions, however, and one may appear slightly more yellow or blue.

For applications requiring strong visual consistency, these differences can become important.

Examples include:

Premium packaging

Books

Catalogues

Corporate stationery

Labels

Photographic applications

Decorative paper

Printing substrates

Specialty paper

Paperboard

Tissue products

Color consistency can therefore affect both manufacturing quality and the appearance of the final product.

What Is Paper Color Measurement?

Paper Color Measurement is the instrumental evaluation of the optical color characteristics of paper under specified conditions.

A suitable color-measurement instrument illuminates the paper and measures the reflected light.

The resulting data can then be converted into standardized color values.

One widely used color system is CIELAB, represented by:

L* – Lightness

a* – Red-green direction

b* – Yellow-blue direction

Together, these coordinates provide a numerical description of the measured color.

Understanding L* in Paper Measurement

L* represents lightness.

The scale runs conceptually from:

0 = black

to

100 = white

A high L* value indicates a light sample.

For white and light-colored papers, L* is often relatively high.

Suppose two paper samples produce:

Paper A: L* = 96.2

Paper B: L* = 93.8

Paper A is lighter according to this measurement.

However, lightness alone does not fully describe the paper’s appearance.

This is why a* and b* are also important.

Understanding a* in Paper Color

The a* coordinate describes the red-green color direction.

Positive a* values move toward red.

Negative a* values move toward green.

Even small changes can help quantify subtle differences between paper batches.

Understanding b* in Paper Color

The b* coordinate describes the yellow-blue direction.

Positive b* values move toward yellow.

Negative b* values move toward blue.

This coordinate can be particularly useful for white paper because subtle yellow-blue differences strongly influence how people perceive the shade of white.

A paper with a slightly negative b* value may appear relatively bluish, while a positive b* value indicates movement toward yellow.

Why Visual Inspection Alone Is Not Enough

Human color perception is influenced by many factors.

These include:

Lighting conditions

Observer differences

Surrounding colors

Viewing angle

Background

Time spent viewing the sample

Paper texture

Gloss

Optical brightening effects

This means two operators may describe the same paper differently.

Instrumental color measurement of paper reduces this subjectivity.

Instead of:

“Batch B looks slightly yellower,”

a laboratory can report measured L*, a*, b* values and an appropriate color difference.

What Is ΔE in Paper Color Measurement?

When comparing two colors, manufacturers often need a single value representing the overall difference.

This is where color difference, commonly represented using ΔE metrics, becomes useful.

A reference paper can be measured and stored as a standard.

A new production batch can then be measured against it.

The instrument or software can calculate the difference.

Different ΔE formulas exist, so the exact color-difference equation used should be specified.

A production workflow might therefore look like:

Approved Paper Standard → Production Sample → Instrument Measurement → Color Difference → Quality Decision

This is much more objective than relying only on visual comparison.

Paper Color vs Paper Whiteness vs Paper Brightness

This distinction is extremely important.

The terms color, whiteness and brightness are sometimes used interchangeably in everyday conversation, but technically they describe different aspects of paper appearance.

Paper Color

Color describes the overall measured appearance and may be represented using coordinates such as Lab*.

Paper Whiteness

Whiteness is an index calculated according to a defined method intended to describe how white a material appears under specified conditions.

Paper Brightness

Brightness is a specific optical property measured according to an applicable standardized method and should not simply be treated as another name for whiteness.

Therefore:

Brightness ≠ Whiteness ≠ L*

They are related to optical appearance but are not interchangeable.

Why Paper Manufacturers Measure Color

Paper manufacturers may use instrumental color measurement for:

Raw-material control

Production monitoring

Batch matching

Shade control

Whiteness evaluation

Yellowing studies

Customer specification compliance

Product development

Supplier comparison

Quality documentation

Troubleshooting

Color measurement turns paper appearance into useful process data.

How to Measure Color in Paper

Accurate Color Measurement in Paper requires more than simply placing a sheet in front of an instrument.

Paper is an optically complex material. Thickness, opacity, surface finish, texture, coatings, optical brightening agents and backing conditions can influence measurements.

Therefore, standardized sample preparation and measurement conditions are essential.

Step 1: Select a Representative Paper Sample

The sample should represent the batch being evaluated.

If paper color varies across the web or sheet, multiple measurement positions may be necessary.

A quality-control procedure might specify measurements at defined locations across a sheet or roll.

This helps identify variation that a single measurement could miss.

Step 2: Condition the Paper When Required

Paper can interact with environmental moisture.

Temperature and humidity can affect certain physical properties and may also influence how samples are handled and compared.

Where required by the applicable test method or internal QC procedure, paper samples should be conditioned under defined environmental conditions before measurement.

Consistency is essential.

Step 3: Ensure the Surface Is Clean

The measurement area should be free from unintended contamination.

Avoid:

Fingerprints

Dust

Oil

Ink marks

Scratches

Unintended stains

Foreign particles

These can influence the measurement.

Step 4: Choose the Correct Side

Some paper products have different properties on each side.

If the product has a designated printing side, coated side or functional surface, the test procedure should specify which side is measured.

Do not randomly switch sides between samples.

Step 5: Use Consistent Backing Conditions

Backing can influence measurements, especially when paper is not fully opaque.

Depending on the test method, measurements may require a specified backing or a defined stack of sheets.

For example, measuring one thin sheet over a dark surface may produce a different result from measuring the same sheet over multiple identical sheets.

The backing condition should therefore be standardized.

Step 6: Calibrate the Instrument

Before measuring paper, calibrate the instrument according to the manufacturer’s recommended procedure.

Calibration establishes appropriate reference conditions for reliable measurements.

Routine verification should also be performed according to the laboratory’s quality procedure.

Step 7: Select the Appropriate Measurement Conditions

Depending on the application and instrument, measurement settings may include:

Illuminant

Standard observer

Measurement geometry

Measurement aperture

Color scale

Specular component settings

UV conditions where relevant

Whiteness or yellowness calculations

The same settings should be maintained when comparing samples.

Step 8: Position the Paper Correctly

The paper should lie consistently against the measurement port or sample holder.

Wrinkles, folds, gaps and inconsistent positioning should be avoided.

For textured paper, multiple measurements may be useful.

Step 9: Take Multiple Measurements

A single measurement represents only one area.

For production paper, a more robust procedure may involve measurements at multiple positions.

For example:

Top

Center

Bottom

Left

Right

The readings can then be evaluated individually or averaged according to the defined QC procedure.

Step 10: Record Lab* Values

A hypothetical paper sample might measure:

L* = 95.8

a* = 0.2

b* = 1.7

These numbers provide an objective description of its measured color under the selected conditions.

A second production batch can then be compared numerically.

Color Difference Measurement in Paper

Suppose an approved paper standard has:

L* = 96.0

a* = 0.1

b* = 1.2

A production batch measures:

L* = 95.4

a* = 0.2

b* = 2.0

The new batch is somewhat darker and has shifted further in the yellow direction according to these hypothetical values.

Color-difference calculations can summarize the overall difference.

This enables manufacturers to establish tolerance limits based on product requirements.

Paper Whiteness Measurement

Whiteness is important for many paper grades.

However, Whiteness Index is not simply the L* value.

Whiteness is calculated according to a specified formula and measurement conditions.

Paper manufacturers should therefore identify which whiteness method is required by:

Product specifications

Customer requirements

Industry standards

Internal QC procedures

Different methods should not be mixed when historical comparison is required.

Paper Brightness Measurement

Brightness is another widely used paper optical parameter.

It is particularly important to understand that paper brightness has a specific technical definition under standardized methods.

A paper with high brightness does not necessarily have identical whiteness or color coordinates to another paper with similar brightness.

Therefore, manufacturers should report the actual measured property rather than using brightness and whiteness as synonyms.

Yellowness Index of Paper

Paper can develop yellow coloration due to factors such as:

Aging

Heat

Light exposure

Raw-material variation

Storage conditions

Chemical changes

Depending on the product and test method, Yellowness Index (YI) or CIELAB b* can help monitor yellow-related changes.

YI and b* should not be treated as the same parameter.

b* is the yellow-blue coordinate in CIELAB.

YI is a calculated index according to a defined method.

Optical Brightening Agents and Paper Measurement

Many white papers use optical brightening agents, often abbreviated as OBAs.

These materials can influence perceived whiteness by interacting with ultraviolet radiation and emitting visible light.

As a result, the UV content of the measurement illumination can become important when evaluating papers containing optical brighteners.

If two instruments have substantially different UV conditions, measurements of OBA-containing papers may differ.

This is why standardized measurement conditions are particularly important in paper color measurement.

Measurement Aperture

The measurement aperture determines the area of the sample being evaluated.

For uniform paper, a standard measurement area may provide repeatable results.

For patterned, textured or heterogeneous papers, a larger measurement area or multiple measurements may better represent the sample.

The appropriate aperture depends on the application and instrument.

Applications of Color Measurement in the Paper Industry

Instrumental paper color measurement is used throughout the paper value chain—from manufacturing and converting to printing and packaging.

Paper Manufacturing Quality Control

Paper mills need to maintain consistent appearance across large production volumes.

Color measurement can be performed during or after production to compare paper against an approved target.

If measurements begin drifting from the specification, production teams can investigate potential causes.

These may include:

Raw materials

Pulp characteristics

Dyes

Fillers

Optical brighteners

Coatings

Process conditions

Water chemistry

Production changes

Color measurement therefore supports both final inspection and process control.

Printing Paper

Printing substrates need consistent color because the paper itself influences the appearance of printed inks.

Imagine printing the same artwork on:

A neutral white sheet

A blue-white sheet

A cream sheet

The printed result can appear different even if identical inks are used.

For high-quality printing, controlling substrate color can therefore be important.

Packaging Paper and Paperboard

Packaging has become highly appearance-driven.

Brand colors need to remain visually consistent across cartons, labels and printed packaging.

Variation in the underlying paperboard can influence final printed appearance.

Instrumental measurement helps packaging manufacturers control the substrate before printing and converting.

Applications include:

Folding cartons

Luxury packaging

Food packaging

Pharmaceutical packaging

Cosmetic packaging

Retail boxes

Labels

Paper-based displays

Coated Paper

Coated papers are engineered to provide particular appearance and printing characteristics.

Color measurement can help monitor:

Base shade

Coating consistency

Whiteness

Yellow-blue variation

Batch differences

Surface-related appearance changes

When coatings contain pigments and optical brighteners, measurement conditions should be carefully standardized.

Uncoated Paper

Office paper, writing paper, book paper and other uncoated grades can also require strict shade consistency.

Customers may immediately notice when sheets from different batches are mixed together.

A paper color measurement instrument helps prevent this by comparing production against stored standards.

Tissue Paper

Tissue products may be produced in white, pastel or colored varieties.

Color consistency can be important for:

Facial tissue

Toilet tissue

Napkins

Kitchen towels

Decorative tissue

Instrumental measurement helps manufacturers maintain consistent appearance between production runs.

Specialty Paper

Specialty paper applications can include:

Security paper

Decorative paper

Technical paper

Release paper

Filter-related paper

Art paper

Premium stationery

Each application can have its own color requirements.

Recycled Paper

Recycled fiber sources can introduce greater variation in raw-material appearance.

Color measurement can help manufacturers monitor the resulting paper and adjust production processes when necessary.

Depending on the product, manufacturers may monitor:

Lab*

Brightness

Whiteness

Yellowness

Color difference

This helps maintain a more consistent final product even when raw materials vary.

Paper Aging Studies

Paper can change color over time.

Aging may be influenced by:

Light

Heat

Humidity

Chemical composition

Storage environment

Oxidation

Raw materials

Researchers can measure paper before and after controlled aging.

For example:

Initial sample → Aging exposure → Intermediate measurement → Final measurement

Changes in L*, a*, b*, YI or other relevant parameters can then be quantified.

Archival and Conservation Applications

Color measurement can also support research involving documents, archival papers and conservation materials.

Non-destructive or minimally invasive optical measurement methods, where suitable, can help document changes in appearance over time.

The exact method should be selected according to conservation requirements.

Paper Supplier Comparison

Suppose a printer purchases nominally the same white paper from three suppliers.

Visual inspection may indicate that all are white.

Instrumental measurement may reveal differences in:

Lightness

Yellow-blue shade

Red-green shade

Whiteness

Brightness

These differences can affect printing and final appearance.

Supplier comparison therefore becomes more objective when supported by numerical data.

Incoming Quality Control

Converters, printers and packaging manufacturers can measure incoming paper before using it in production.

An incoming QC procedure might include:

Identify batch.

Condition sample if required.

Measure paper.

Compare with approved standard.

Review color difference.

Accept or investigate according to specification.

This can prevent off-shade material from entering production.

Color Measurement in Paper R&D

Research and development teams can use instrumental color measurement to investigate how changes in formulation affect paper appearance.

For example, researchers may vary:

Pulp blend

Pigment concentration

Dye concentration

Filler level

Coating formulation

Optical brightener level

Processing conditions

Each experimental sample can be measured numerically.

This allows researchers to correlate formulation changes with appearance.

Choosing a Color Measurement Instrument for Paper and Best QC Practices

Selecting an instrument for Color Measurement in Paper requires understanding the material, applicable standards and required optical parameters.

Not every color measurement application has identical requirements.

Colorimeter vs Spectrophotometer for Paper

Both terms are commonly searched when users look for paper color measurement solutions.

A colorimeter measures color using a defined optical sensing approach and can be suitable for many color comparison applications.

A spectrophotometer measures spectral reflectance or transmittance across a range of wavelengths and uses that spectral information to calculate colorimetric values.

For demanding industrial paper applications—particularly where whiteness, brightness, optical brighteners, spectral data or detailed color analysis are important—the required instrument should be selected based on the applicable standard and measurement objective.

The correct choice should therefore be driven by the application rather than by the instrument name alone.

Important Features for Paper Color Measurement

1. Repeatability

Paper manufacturers may need to detect relatively small differences between batches.

Good instrument repeatability is therefore important.

2. Appropriate Measurement Geometry

The optical geometry should match the application and applicable test procedure.

Measurements from substantially different geometries should not automatically be treated as interchangeable.

3. UV Control Where Required

For papers containing optical brightening agents, control of UV content can be particularly important.

The instrument configuration should support the required measurement method.

4. Suitable Measurement Area

The aperture should be appropriate for the sample.

A larger measurement area can be useful for some non-uniform materials.

5. Support for Relevant Color Scales

Depending on requirements, users may need:

CIELAB Lab*

XYZ

Color difference

Whiteness indices

Yellowness indices

Other paper-related optical parameters where supported

6. Quality-Control Software

Software can make routine paper testing much more efficient.

Useful functions can include:

Standard storage

Tolerance setting

Batch comparison

Pass/fail evaluation

Trend analysis

Data export

Reporting

Historical comparison

7. Easy Sample Positioning

Paper testing often involves large numbers of samples.

Efficient positioning and measurement can improve laboratory productivity.

Best Practices for Paper Color Measurement

Keep Measurement Conditions Constant

Always compare samples using equivalent settings.

Use Consistent Sample Backing

Backing can influence results when paper is not fully opaque.

Measure the Correct Side

Do not switch randomly between paper surfaces.

Keep Samples Clean

Avoid fingerprints and contamination.

Use Multiple Readings When Necessary

Paper can contain local variation.

Monitor Instrument Performance

Follow calibration and verification procedures.

Store Approved Standards

Reference data enables reliable production comparison.

Establish Product-Specific Tolerances

There is no universal ΔE, L*, whiteness or brightness tolerance suitable for every paper product.

Limits should be based on:

Customer requirements

Visual acceptability

Product specifications

Historical production capability

Applicable standards

End-use requirements

Paper Color Measurement for Batch Consistency

Batch consistency is one of the strongest reasons for implementing instrumental measurement.

Consider a company producing premium white packaging board.

A reference batch is approved by the customer.

Its color data is stored.

Every future batch is measured against that reference.

Instead of relying on an operator to decide whether the board “looks close enough,” the company has numerical information.

This improves communication between:

Production

Quality control

R&D

Suppliers

Converters

Printers

Customers

Using Color Measurement for Process Optimization

Color data can also reveal trends.

Suppose b* gradually increases over multiple production batches.

Even if every batch still passes the final specification, the trend indicates that the product is moving toward a more yellow appearance.

Production teams can investigate the process before an out-of-specification batch occurs.

This makes instrumental color measurement valuable for preventive quality control.

Frequently Asked Questions About Color Measurement in Paper

How is color measured in paper?

Paper color can be measured instrumentally under defined conditions. Suitable instruments measure reflected light and calculate standardized color coordinates such as CIELAB L*, a* and b*.

Which instrument is used for paper color measurement?

Colorimeters and spectrophotometers can be used depending on the application. The appropriate instrument should support the required measurement geometry, color scales, optical parameters and applicable standards.

What is Lab* in paper?

L* represents lightness, a* represents the red-green direction, and b* represents the yellow-blue direction.

What does b* indicate in white paper?

Positive b* indicates movement toward yellow, while negative b* indicates movement toward blue.

Is paper brightness the same as whiteness?

No. Brightness and whiteness are different optical parameters defined by their respective measurement methods.

Is L* the same as paper whiteness?

No. L* is the CIELAB lightness coordinate. Whiteness is a separately calculated index according to a defined method.

Why does white paper sometimes look blue?

A paper can have a slight blue tint because of its spectral characteristics and, in some cases, the influence of optical brightening agents. Measurement conditions, particularly UV content where OBAs are present, can affect measured appearance.

Can Yellowness Index be measured in paper?

Yes, where appropriate to the application and selected measurement method. YI provides information about yellow coloration and should not be confused with CIELAB b*.

Why are multiple paper measurements recommended?

Paper can vary across its surface. Multiple readings can provide a better representation of a sheet or production batch than a single measurement.

Can paper color change with aging?

Yes. Light, heat, humidity, oxidation, material composition and storage conditions can contribute to appearance changes over time.

Conclusion

Color Measurement in Paper is an important part of modern paper manufacturing, printing, packaging, converting, research and quality control.

Although two paper samples may both be described as “white,” instrumental measurement can reveal meaningful differences in lightness, red-green shade, yellow-blue shade, whiteness, brightness, yellowness and overall color difference.

Using standardized color measurement allows manufacturers to replace subjective descriptions with numerical data.

CIELAB L*, a* and b* values provide an objective description of paper color, while color-difference metrics can quantify differences between a production sample and an approved reference.

Other optical parameters such as paper whiteness, paper brightness and Yellowness Index can provide additional information when measured according to the appropriate method.

It is important to understand that these parameters are related but are not interchangeable.

Paper brightness is not the same as paper whiteness. Whiteness is not the same as L*. Yellowness Index is not the same as b*.

Reliable paper color measurement also requires careful control of sample preparation and measurement conditions.

Paper side, backing, thickness, opacity, texture, coating, measurement geometry, aperture, illuminant, observer and UV conditions can all influence results.

This becomes particularly important when paper contains optical brightening agents (OBAs).

When the measurement procedure is properly standardized, a suitable paper color measurement instrument can support:

Batch-to-batch color consistency

Paper whiteness control

Shade matching

Incoming material inspection

Printing substrate control

Packaging quality

Supplier comparison

Paper aging studies

R&D

Process optimization

Troubleshooting

Customer specifications

Quality documentation

For paper mills, printers, packaging manufacturers and converters, objective color data provides a common language for discussing appearance.

Instead of saying:

“This batch looks slightly different.”

quality teams can determine exactly how the color changed, in which direction it changed and how large the difference is.

That is the key advantage of modern Color Measurement in Paper—turning paper appearance into measurable, repeatable and actionable quality data.