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International Standards

ISO 5631-2

Introducing ISO 5631-2 - Industrial Physics  

ISO 5631-2 is an ISO international test method that helps you to measure the color of paper and board using the diffuse reflectance method, with the elimination of specular gloss. 

Part two of the ISO 5631 diffuse reflectance method was created for color paper testing in outdoor daylight conditions. The light reflected from your sample is analyzed using either a tristimulus-filter colorimeter or by an abridged spectrophotometer. The color coordinates are then calculated for D65/10° conditions. 

This ISO paper color testing approach can be used to determine the color of papers or boards that contain fluorescent whitening agents. This is as long as the UV content of the sample’s illumination has been previously adjusted to give the calibrated colourimetric value. To do this you’ll need a fluorescent reference standard with an assigned CIE whiteness (D65/10°) value from an authorized laboratory.  

If you’re working with colored papers and boards that incorporate fluorescent dyes or pigments then ISO 5361-2 testing isn’t an appropriate testing standard. Give us a call, we would happily talk you through any alternative options.  

ISO 5631-2 diffuse reflectance method definitions

Within the ISO 5631-2 color paper testing documents there are a number of key definitions that you’ll need to familiarize yourself with before you start your own tests.  

Radiance factor: the ratio of the radiance of a surface element of a body. This is in the direction delimited by a given cone, with its apex at the surface element, to that of the perfect reflecting diffuser under the same conditions of illumination. 

Intrinsic radiance factor: the radiance factor of a layer - or pad of material - thick enough to be opaque. Such that increasing the thickness of the pad, by doubling the number of sheets, results in no change in the measured radiance factor. 

Reflectance factor: the ratio of the radiation reflected by a surface element of a body in the direction delimited by a given cone. With its apex at the surface element to that of the perfect reflecting diffuser, under the same conditions of illumination 

Intrinsic reflectance factor: the reflectance factor of a layer - or pad of material - thick enough to be opaque, such that increasing the thickness of the pad by doubling the number of sheets results in no change in the measured reflectance factor. 

Tristimulus values: X10, Y10, Z10 the amount of the three reference color stimuli, in a given chromatic system, required to match the stimulus considered. 

CIELAB color space: three-dimensional, approximately uniform color space, produced by plotting, in rectangular coordinates L*, a*, b*, quantities defined by a formulae given in the ISO 5631-2 documents.  

ISO 5631-2 spectrophotometer devices 

So, how can Industrial Physics improve your ISO 5631-2 color testing?  

Technidyne ColorTouch®X ISO

An advanced touchscreen color spectrophotometer that measures color difference, brightness, whiteness, opacity and more. The ColorTouch® X ISO uses color testing methods that meet all the most common ISO and TAPPI spectrophotometer standards. 

Technidyne ColorTouch® PC

The ColorTouch® PC is a powerful spectrophotometer that gives you complete control over the optical properties of your paper based products. Brought to you by Technidyne, our specialist optical, surface, and physical property testing brand, The ColorTouch® PC inspects everything from ISO brightness, color and color difference to fluorescence and opacity. 

Need ISO 5361-2 testing solutions? Get in touch

We’ve learnt a thing or two about the diffuse reflectance method and color testing over the decades. We like to share the lessons learnt and the insight we have gained. Why not check out our blog on the main uses of a spectrophotometer, or this one that explores some different methods of testing the physical properties of paper? 

If you have any questions about ISO 5631-2, spectrophotometers or paper color testing in general, then please just get in touch!

Contact us - Industrial Physics

Your global test and inspection partner for ISO 5631-2