Whiteness Tester for Paper

What is the Whiteness Tester for Paper?

A whiteness tester derives the CIE whiteness index and tint from the colour coordinates of a paper specimen under illuminant D65 or C. It quantifies how white a sheet appears, including the effect of fluorescent whitening agents.

Overview

Whiteness is not a direct reflectance measurement but a formula applied to the tristimulus values of the specimen, which requires measurements at several wavelengths across the visible range. A tristimulus colorimeter or spectrophotometer therefore forms the basis of the instrument, with a tungsten or xenon source whose ultraviolet content is controlled, because whiteness values of papers containing fluorescent whiteners depend on the ultraviolet in the illumination. Results are reported as whiteness index, tint and often yellowness, using the illuminant and observer combination named in the standard. Because the calculation uses the whole visible spectrum, the instrument distinguishes papers that have the same ISO brightness but different hue, which is important for shade matching in coated and writing grades.

How does it work?

A brightness or reflectance instrument illuminates the specimen diffusely and measures the light reflected at right angles, using a defined geometry, illuminant and observer so that results are reproducible between laboratories. ISO brightness is the diffuse blue reflectance factor measured with an effective wavelength of 457 nm under illuminant C, and it is highly sensitive to fluorescent whitening agents. Whiteness is a single number derived from the full colour coordinates under illuminant D65 or C, while yellowness, tint and shade are obtained from the same measurement. Opacity is the ratio of reflectance of a stack-backed specimen to that of an infinite stack, and can be determined by diffuse reflectance or by the contrast ratio of luminous reflectance. Gloss is measured separately at a fixed angle of incidence, because it depends on surface finish rather than on bulk optical properties.

What are the key features?

• CIE whiteness index calculation from tristimulus values
• Illuminants D65 and C with controlled UV content
• Tint, yellowness and shade reporting
• White standard calibration per measurement series
• Optional UV cut-off filter for fluorescence control
• Comparison against grade-specific targets

What are the technical specifications?

A typical whiteness tester for paper configuration offers whiteness indices of CIE whiteness per ISO 11475 or 11476, illuminants of D65 and C with defined UV content, observer of 2° or 10° standard observer, spectral range of 400–700 nm at 10 nm intervals, repeatability of ±0.1 whiteness unit and measuring area of 10–30 mm diameter. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Whiteness Tester for Paper is used in whiteness specification testing of coated papers, shade control in writing and office papers, fluorescent whitening agent performance checks and incoming inspection of pulp whiteness. Across the wider Brightness Testing class, laboratories also deploy it for brightness verification of printing and writing papers, whiteness and shade control for coated papers and opacity checks for lightweight printing grades.

Which standards and certifications apply?

Relevant standards and methods include ISO 2470-1, ISO 2470-2, ISO 2471, ISO 11475, ISO 11476, ISO 5631-1, TAPPI T452, TAPPI T525 and IEC 61010-1. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Keep the instrument calibrated with certified standards traceable to a national laboratory, and check the white standard and black trap at the start of each measurement series. Stack at least the number of sheets the method requires behind the specimen to ensure an opaque backing, because too few sheets allow the backing plate to influence the reading. Condition specimens to the standard atmosphere and protect them from light and heat, since fluorescent whitening agents bleach and papers yellow on exposure. Clean the measuring aperture and the standard regularly, avoid touching the measurement area of the specimen with fingers, and record the geometry, illuminant and observer with every result.

How do I select the right Whiteness Tester for Paper?

Choose a whiteness tester when the specification is expressed as a CIE whiteness index or when shade and tint must be controlled alongside brightness. Confirm that the standard you follow specifies the illuminant and observer combination, and check whether a UV filter or adjustable ultraviolet content is required for fluorescence control.

How does it compare with other Brightness Testing variants?

Match the instrument to the parameter named in the product standard. ISO brightness requires a 457 nm effective wavelength with the specified geometry, while D65 whiteness, colour and yellowness require a spectrophotometer covering the visible range under standard illuminants and observers. Opacity is measured with either a dedicated contrast ratio instrument or a spectrophotometer able to compute it from reflectance data. Gloss needs a dedicated meter with the correct incidence angle for the paper grade. Where the laboratory also verifies print appearance or matches shades, a benchtop spectrophotometer with both measurement geometries and a full set of illuminant and observer combinations is more useful than a single purpose meter, even though it costs more.