Metamerism: The Underlying Problem of Colour Matching

Colour isn’t just what we see, it’s what light tricks us into believing. Colour is something more than a sense of sight. Where quality is defined as appearance, printing, textiles, pigments, and coatings, consistent colour in diverse lighting conditions is essential. Even with perfect technology, though, the colours appear to be a match under a certain source and not with another. This misleading visual illusion is metamerism. In this article, we’ll explore what metamerism is, where it occurs, its impact on various industries, and how it can be detected, controlled, and corrected.

What is Metamerism?

Metamerism is an optical phenomenon whereby two colours appear to be the same when viewed under one source of illumination but not when viewed under another. Two metamers appear different under one source of light but different under another. These colours are called metamers. They might look the same under one type of light, but the way they reflect light is very different.

For instance, the two shoes and the bag are the same black colour in a store, but look mismatched when out in the sun. This is not due to faulty dyes or prints, but due to the very nature of colour perception, due to the nature of light and the composition of material.

The Fundamental Principle of Metamerism

Metamerism theory is founded on how the human eye can see colour. There are three types of cone cells (one for red, one for green, and one for blue wavelengths) in the eyes that transform the light coming from objects. When two quite different spectral combinations stimulate the same cones of the same light source, the brain can decide that the colour is the same. But if the illuminant is changed, the spectral balance of the reflected light is changed, so that the cones are stimulated differently by the same objects. So, a match perceived is a mismatch; this is the theory of metameric failure.

Metamerism as a Phenomenon of Optics

Metamerism is an optical phenomenon because it does not occur due to any physical property alteration of objects, but due to the interaction of materials, light, and the human eye. It indicates the insufficiency of visual inspection alone to ascertain colour tolerance, especially in high-quality scenarios.

Types of metamerism are:

1. Define Metamerism:

 A condition in which two colours match under a given illuminant but do not match under another.

2. Observer Metamerism: 

Two observers perceive colour differently due to variations in their vision.

3. Geometric Metamerism: 

Effects caused by differences in directions of sight or surface features that influence the reflectance of light.

The Occurrence of Metamerism

Metamerism is a condition where the products are made of disparate materials or dyes that show different light reflection but appear to have the same hue. This commonly occurs in:

1. Paints and coatings, whose various pigments possess varied chemical compositions.

2. Textiles, whose natural and man-made fibres react differently to various lights.

3. Printing, particularly with CMYK colour models, on a variety of substrates.

4. Consumer products, including appliances, furniture, or car interiors, which are composed of multi-sourced parts.

The problem becomes noticeable under lights like fluorescent, LED, or natural daylight because these light sources give off uneven mixes of wavelengths.

Origin of Metamerism

The word "metamerism" comes from the Greek metameres, meaning "of a different part." The word in colour science goes back to the 19th century when scientists first started studying how one colour stimulus could be matched by various spectral combinations.

Recent understanding of metamerism came with the inventions of colourimetry and spectrophotometry, by which colour reflectance and metameric indices can be measured quantitatively.

What is Metamerism in Print?

Metamerism is a major control problem with printing. A picture printed in the press might be flawless, but it shifts colour when exposed to store lighting. It occurs especially when printing process inks and spot colours, or when printing on varying stocks of paper.

Steps to manage metamerism in printing:

1. Standardise the lighting conditions used during proofing.

2. Spectral reflectance as recorded by spectrophotometers (also provided by Threenh).

3.  Choose those colour profiles with a lesser illuminant-dependent shift.

What is Metamerism in Painting?

In coatings and paints, particularly in industrial and automotive uses, you must be the same shade of colour under all lighting conditions. Metamerism results when different pigments or formulations are applied from batch to batch or surface to surface.

Paint metamerism is caused by:

1. Particle size and pigment composition.

2.  Binder and solvent variation.

3. Substrate surface energy and roughness.

To minimise metameric mismatches:

1. Use source pigments with similar spectral reflectance curves.

2. Use standardised light booths in quality checks.

3. Perform spectrophotometric analyses.

Metamerism in Industrial Coatings: Principles, Colour Matching Problems and Solutions

Industrial finishes are subjected to more rigorous appearance, brand, and functional specifications, and colour stability testing. The most typical market segments affected are appliance, automotive, aerospace, and consumer electronics.

Challenges

1. Highly intricate multilayer films.

2. Various textures or gloss surfaces.

3.  Metal and plastic integration.

Solutions:

1. Use electronic colour communication devices to transmit actual spectral information.

2.  Impose strict colour shift tolerances on various light sources.

3. Use appropriate illumination standards like D65, A, and TL84 on the manufacturing and inspection floor.

What is Textile Metamerism?

Textile manufacturing is prone to metamerism when different fibres (like polyester and cotton) are coloured individually but are meant to be compatible. The colour may react differently under light, as regards dye uptake change and fibre composition.

Steps involved in managing textile metamerism:

1. Use dyes of comparable lightfastness qualities.

2. Vision examination under different light sources.

3. Use instrumental colour matching with spectrophotometers.

How to manage metamerism?

To control metamerism, there should be a balance of scientific equipment, together with standardised production, design, and quality control procedures. The methods are:

Standard Illumination: 

Test colours under standard illuminations such as D65 (daylight), A (incandescent), or TL84 (fluorescent).

Spectral Matching: 

Choose materials and dyes that have comparable spectral reflectance curves to minimise the possibility of metamere.

Instrumental Measurement: 

Measure colour properties using spectrophotometers rather than visual inspection.

Material Consistency: 

Never mix materials with different inherent reflective properties.

Spectrophotometers: The Key to Accurate Colour Matching

Effective detection and control of metamerism rely to a significant degree upon objective measurement of colour versus subjective visual examination. That is where high-precision spectrophotometers may be of use, with an important function in measurement of spectral reflectance as well as in guaranteeing colour stability in changing lighting conditions. For such professionals seeking dependable solutions, 3nh is a single-stop solution that offers a complete line of spectrophotimeters specifically designed for applications in printing, coatings, plastics, and textiles. They offer a line of benchtop, multi-angle, and portable instruments that provide precise results for laboratory and in-situ testing. By employing the correct equipment from a reputable organisation like 3nh, selecting a productive piece of kit will make colour matching more straightforward and prevent the expensive metameric failure. 

How to Avoid Metamerism?

Although metamerism can never be completely prevented, its effect can be minimised by the following steps:

Early Planning: 

At the time of product development, evaluate all parts in dissimilar light surroundings.

Material Standardisation: 

Use the same supplier and dye lot to avoid spectral change. 

Cross-functional Coordination: 

Designers, suppliers, and manufacturers should be able to exchange standard colour specs such as CIE Lab values.

How to overcome Metamerism?

If metamerism is found post-production, it can be rectified by:

1. Colourant refinement to advance them towards spectral match.

2. Adjustment of lighting within the display area to reduce visibility of mismatches. 

3. Informing consumers, or buyers, about how light affects the perception of colour. Advanced colour matching instruments and databases also simulate metamerism conditions to choose the best blend before actual production. 

The Inspiration from Metamerism 

Interestingly, metamerism has taken ideas from outside the colour correction arena. It has created: 

Lighting design: 

Development of full-spectrum LEDs that minimise colour shifts. 

Computer graphics: 

High-quality material rendering under different light sources. 

Virtual prototyping: 

Product appearance simulation under various lighting conditions before actual manufacturing. 

Even in biology, metamerism is utilised in the description of body segmentation within an organism, further showing the cross-disciplinary nature of the term. 

The Role of Metamerism in Product Colour Stability. 

For product colour consistency of appearance, brand reputation, and customer satisfaction, metamerism is a liability. It is particularly against this consistency because the customer views the product under home, office, or daylight lighting. 

Companies that ignore metamerism risk:

1. Additional product returns.

2. Poor brand reputation.

3. Rework or reformulation costs.

Conversely, companies adopting colour science and metamerism pre-emptive control can gain a competitive advantage with product consistency and confidence. Solutions to Accurate Colour Management Advanced colour management systems may identify and remove metameric colour differences before forwarding it to the customers.

 Solutions include:

1. Reflectance spectrum analysing spectrophotometers, such as the ones provided by Threenh.

2. Metamerism colour matches computer simulations for various illuminants.

3. Variable light source paint booths to check immediately by sight.

These include companies like 3nh, providing complete solutions for accurate colour communication and colour quality control in colour-critical applications. Metamerism is an imperceptible phenomenon, yet it has a gigantic consequence for colour matching and quality perception. As consumer demand for visual similarity increases, industries must answer with scientific knowledge and technological assistance. 

Through metamerism identification, detection, and control, producers can guarantee colour consistency, protect brand reputation, and offer a more consistent visual experience for consumers. Whether you're installing car bumpers onto body panels or matching fabric swatches for clothing design, metamerism sensitivity is no longer optional; it's necessary.

To ensure your colours never deceive the eye again, invest in advanced spectrophotometers provided by 3nh, such as the TS8560 Benchtop Grating Spectrophotometer or the TS8520 Benchtop Grating Spectrophotometer and colour management tools.