Pigments: The oldest nanomaterials in human history facing modern day challenges

Cave painting

People tend to think of nanomaterials as something new, innovative, and fancy, coming up since just a few decades. Actually, quite the opposite is true: Mankind used nanomaterials on a regular basis in the stone age, more than 30.000 years before they discovered how to build a wheel and almost 40.000 years before the first iron was smelted in Europe.

The famous drawings in the Chauvet cave in France date back to 35.000 B.C. The pigments in these cave drawings are mostly earthy colourants based on the pigments iron oxides, manganese oxides and carbon black – at least that is what we would call them nowadays. And in ancient Egypt, the soot of oil lamps was used to make black pigments of high opacity and stability – ideal for putting clear black writing on papyrus. It just so happens the Egyptians did not know that the soot they were using contained nanoparticles.

People in the stone age did not think about the size of the pigments. They did not manufacture these nanomaterials intentionally in this size scale but simply used the best available option. Therefore, it is important to remember that pigments are not intentional nanomaterials but simply happen to show the best colouring properties as they have a similar diameter to the wavelength of visible light.

So many pigments are only nanomaterials by chance – with respect to the time pigments are being used by mankind – as the very newly introduced definition happens to touch the typical size range.


Ancient products in modern times

Today, our world is by far more colourful than in former times. Inorganic, organic, and metallic pigments as well as many dyes extend the possibilities to bring colour to our life. Pigments and fillers were not “invented” just recently under nanotechnology promotion programs. They have been used for centuries, or they are the results of industrial research from the past hundred years. Of course, the way of producing them is different today, in industrial processes fully developed in the last centuries.

While the educts for inorganic pigments are often still the same ores used by our ancestors, the production processes are highly controlled nowadays to guarantee a constantly high quality of the product, to comply with legal requirements, and to protect consumer safety.

By constant optimisation, undesired by-products like heavy metal residues are reduced or even eliminated and the resource and energy efficiency of the production processes are increased. The pigments themselves, however, have not changed that much.

In case of pigments, the introduction of nano-specific requirements in some pieces of legislation increased the legislative burden a lot. With the introduction of a definition of nanomaterials based on a particle size below 100 nm, authorities tried to minimize potential risks from newly developed nanomaterials for which the research for potential risks was practically still in its infancy at the beginning of commercialisation.

Many pigments have been produced in the same way over several decades without any concerns on employee, consumer, or environmental safety. Nevertheless, with nano-specific requirements in force, the reporting and safety obligations increased even though the product itself or information on its safety have not changed at all.


Eurocolour: bridging industry and legislation

Eurocolour logoOne of the important tasks of Eurocolour is to keep its members up to date with recent legislative changes. The represented pigment, dye, and filler producers often face similar challenges, giving Eurocolour the possibility to act as a single voice for these industries. Besides publishing press releases and position papers, Eurocolour participates in various legislative processes, provides input into public consultations and acts as contact for authorities, consumers, and other interested parties.

During the last decades, the legislative burden increased immensely in the chemical industry, especially for small and medium sized companies. They often lack the manpower to keep up to date with every regulative change and new law. Thus, Eurocolour informs its members regularly on the latest developments concerning REACH and CLP, relevant product specific regulations and national as well as important international legislation.

In a project started shortly after the EU definition was published, Eurocolour together with the Joint Research Centre (JRC) had comprehensively taken stock of the use of existing measuring methods for commonly used pigments and fillers. Based on the results, it is not possible to recommend one single, commonly used method by industry for identifying a pigment or filler as a nanomaterial. Moreover, much expertise and a solid knowledge of the substance in question are needed to obtain reliable results in particle size measurement.

In the follow-up project Nanodefine, in which Eurocolour participated actively, the outcome was that for most fillers and pigments and other comparable particulate substances, nano status assessment and conclusive determination is feasible only with the most labour and cost intensive methods of elective microscopy.


Various definitions leading to confusion and mistrust

In case of nano-specific requirements, many different responsibilities need to be adhered to. For example, there is still no universal definition for a nanomaterial. Even though EU Commission’s recommendation on the definition of a nanomaterial was published in 2011, so far, nearly every regulation transfers and implements this recommendation slightly differently (e.g. implementation in the cosmetics, food, biocides regulations). So, the same pigment may be a nanomaterial in one product regulation, but not in another.

Unfortunately, no revision of the EU Commission’s recommendation is finalised to date, even though the revision was originally planned for 2014 and rescheduled several times. Consequently, no harmonisation of the definition in the different regulations mentioned above is achieved up to now.

The same goes for the reporting obligations in national nano registers throughout the EU. This leads to much confusion and uncertainty on both sides, with producers and consumers. Additionally, this gives the impression of a non-transparent handling of nanomaterials, resulting in a general mistrust of nanomaterials but also in the competence to handle these materials safely.

Pigments and fillers are used for the colouring and surface structuring of nearly all products found in our daily life. Therefore, in the past, very often questions were raised especially from NGOs whether there is a release of nanoparticles from such products resulting in a potential exposure of consumers. Mostly, consumers are in contact with pigments and fillers only indirectly through objects that are coated or coloured with them. Here, the fine particulate or nanoscale dispersed particles are bound in a firm matrix. This largely excludes an exposure for end users to free pigment or filler nanoparticles – which has been confirmed by different studies, recently for example in the FRiNano project of TU Dresden for the permanent use and ageing of coatings and plastics.


Nano registrations under REACH

With the requirement under the REACH Regulation to include separate nanoforms in the registration dossier from 1 January 2020, the objective was to ensure safe use of nanoforms of substances on the EU market. However, so far, quite the opposite is the case. With the term nanoform, a new, additional definition for nanomaterials is introduced.

The information requirements on these nanoforms shall take care of sufficient consideration in the risk and exposure assessment. Several guidance documents and an update for the software tool IUCLID are developed to facilitate the nano-specific dossier updates. While the idea behind such nano registrations was good, the implementation lacks behind.

The technical means to submit a nano-specific dossier update was given only two months before the deadline, guidance documents were published even later or are still under development.

Most important from Eurocolour’s perspective, there is a divergence between the REACH Annexes and the guidance documents. The requirements in the guidance on the registration of nanoforms go far beyond the original REACH text, e.g. the guidance demands a quantitative analysis of the crystallographic structure while the REACH annexes only require information on the crystallinity.

Thus, instead of bringing clarity more confusion is created, e.g. confusing registrants on what information to provide.


There should be no ban due to a description

So, one of the major challenges for Eurocolour and, consequently, for the European pigments and fillers industry in our modern-day legislative landscape is to ensure that the products can be continued to be used safely and in such a wide range as in the past. This means also to avoid further stigmatisation due to “nano”.

Regarding the different regulations – European and national ones – and the various nano requirements, it is the objective of the industry to avoid unjustified restrictions or even use bans. Pigments and fillers are made nanomaterials by definition, not by intention. That is the reason why nano requirements often hardly fit the reality of these materials. Therefore, downstream legislation should take into account whether or not pigments and fillers are tightly bound to a matrix or paste preventing direct contact with single nanoparticles.

Our knowledge on material safety has increased immensely throughout the last 40.000 years, and it shows that correlations are too complex to be expressed by a single parameter.


What are pigments and fillers?

PigmentsPigments are solid particles. A pigment can be coloured, black, white, or fluorescent.

Unlike dyes, they do not dissolve in the medium in which they are used, whether it be a coating or a plastic, for instance.

A distinction is made between organic, inorganic and metallic pigments. The properties of a pigment that impart colour arise from the interaction of its particles with visible light. Fillers usually consist of very small, solid particles that are likewise insoluble in the application medium.

They are used in plastics and coatings primarily because of their technical properties; the colour they impart is usually only a secondary criterion.

Further reading

Dr Heike Liewald

Dr Heike Liewald, Managing Director - Eurocolour e.V.

Heike Liewald has been working for over 20 years for pigment and filler associations, since 2012 as the management director of Eurocolour e.V.

She is a chemist and holds a PhD in solid state chemistry from the Justus Liebig University Gießen.

Giuliana Beck

Giuliana Beck, Advisor, Specialist for Nanomaterials - German association of producers of pigments and fillers (VdMi)

Giuliana Beck studied chemistry at the Justus Liebig University Gießen and wrote her PhD thesis in the field of physical chemistry.

She joined the German association of producers of pigments and fillers after doing of research on nanomaterials for 6 years.

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