From atoms to pigment droplets (full analysis)

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1. Background

This article addresses a fundamental yet frequently misunderstood aspect of the pigments used in Powder Brows, and Hairstrokes procedures: understanding the various units in pigmentology and their interrelationships.

While it may seem simple, the topic is more nuanced than many realize. For this article, we have utilized interviews with 28 experienced semi-permanent makeup artists, each with over four years of professional practice. Additionally, this article is part of a series reviewed by chemistry, dermatology, and cellular biology experts. The artists contributing to this research are primarily based in European Union countries (15), with eight in the UK and five in the US.

What emerged as quite surprising was the superficial understanding of the biological aspects of pigmentology many artists displayed, often conflating basic terminologies related to sizes. Nevertheless, in terms of overarching conclusions, most of the intuitive beliefs held by the artists were correct from biological and chemical perspectives despite sometimes being fortuitous guesses at their core. This article will explore those five quantity units crucial in pigmentology.

2. Five Basic Units

Basic units for understanding colorant properties

This article will explore the lifespan of typical semi-permanent pigments used in Powder Brows, and Hairstrokes procedures within the skin.

To fully understand the processes related to pigment interaction with the skin, it's crucial first to comprehend certain key terms often misunderstood or used interchangeably by artists. Clarity on these terms will lay the groundwork for our discussion.

Atom - the smallest unit of a chemical element.
Molecule - a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can participate in a chemical reaction.
Pigment Particle - a small, solid particle of pigment, which is the substance that gives semi-permanent makeup its color and affects many other properties.
Aggregate - a cluster of pigment particles that have adhered to one another.
Pigment Drop - a small amount of liquid pigment mixture used in applying semi-permanent makeup.

We will use the example of the organic pigment colorant CI 77266, commonly known as Carbon Black, to elucidate each term in more detail as we progress.

3. Atom

The Fundamental Unit of Chemistry

An atom represents the most basic unit of a chemical element, the smallest particle that still retains the properties of that element. At its core is the nucleus, comprised of positively charged protons and neutral neutrons. Surrounding the nucleus is a cloud of negatively charged electrons bound by electromagnetic forces. Atoms are fundamental to understanding chemical reactions as they are the primary constituents that interact during these processes.

In pigmentology, or the study of pigments, while considering the atom is foundational, it does not provide extensive insights into the behavior of pigments. This is because the properties of pigments are not determined solely by individual atoms but by how these atoms are bonded to form molecules and larger structures.

The Example of Carbon

Several atomic properties are important when examining Carbon, a pivotal element in pigmentology, particularly for pigments like Carbon Black (CI 77266).

Classification as a Nonmetal. Carbon is a nonmetal, which means it can form various types of chemical bonds and molecules, including long chains and rings, crucial for forming complex organic pigments.
Atomic Number. Carbon's atomic number is 6, indicating six protons in its nucleus and defining its element and position in the periodic table.
Atomic Mass. The atomic mass of Carbon is approximately 12.011 atomic mass units (amu), reflecting the average mass of its naturally occurring isotopes and including the weight of protons and neutrons in the nucleus.

Relevance to Pigmentology

While Carbon is relatively light compared to many other elements, this atomic characteristic does not directly inform the practical aspects of using Carbon as a pigment, such as ease of implantation into the skin or color retention. Instead, these aspects are influenced by the form and structure Carbon takes when incorporated into a pigment, whether as a simple elemental form like in Carbon Black or as part of larger, more complex organic molecules.

Therefore, while the atom is the basic building block of matter, in pigmentology, we are more interested in the behavior of collections of atoms—molecules and particles. These larger structures and their interactions with biological systems dictate the properties most relevant to semi-permanent makeup, such as color richness, lightfastness, and longevity.

4. Molecule

A molecule is a collection of at least two atoms bonded together, forming the smallest identifiable unit of a compound that retains the compound's chemical properties. Chemical bonds like covalent, ionic, and metallic are the forces holding atoms together within a molecule.

Hydrocarbon Example - CH4

Hydrocarbons such as methane (CH4) consist solely of hydrogen and carbon. "hydrocarbon" refers to simple molecules and complex polymers with varied structures and physical properties. These range from gases like methane and propane to liquids like hexane and benzene to solids like paraffin wax and naphthalene, exhibiting different phases and forms.

Molecules in Pigmentology

In pigmentology, a colorant's molecular structure contributes to its inherent properties, such as color. However, the practical behavior of a pigment - its solubility, ease of implantation, and retention - can vastly differ depending on its processing and the formation of larger pigment particles. Thus, a molecule alone does not define a pigment's properties.

Implantation and Retention

During semi-permanent makeup procedures, implanting pigment into the skin introduces single molecules and often thousands of atoms united into particles. The behavior of these particles, rather than individual molecules, influences implantation properties. Molecular properties become relevant when they affect the particle's characteristics, especially those influencing charge, polarity, or reactivity, affecting interactions with skin cells and immune cells.

Particle Structure vs. Molecular Structure

Larger pigment particles, forming polymers and paracrystalline structures, exhibit properties significantly different from the individual molecules they comprise. These larger structures govern the pigment's behavior, stability, and degradation over time.

Misconceptions and Incorrect Assumptions

It is a misconception to attribute the degradation reactions of pigments solely to individual molecules' properties. Pigment particles typically break down through the disintegration of aggregates or larger particles. It is crucial to distinguish between the molecular composition of pigments and the behavior of pigments as aggregates or larger particles within the skin.

Thus, while molecular structure is fundamental for understanding the potential properties of colorants, larger particle structures most significantly influence the color, application, retention, and degradation of pigments in semi-permanent makeup. Understanding these particles' behavior in a biological context is critical for differentiating between the molecular composition of pigments and their actual behavior within the skin.

5. Particle

Analyzing the properties of a colorant at the particle level is productive, as the particle is a more relevant unit than the molecule for understanding the behavior of pigments in practical applications. Particles are aggregates of thousands of atoms with a molecular structure and properties significantly different from the individual atoms or molecules they comprise.

Particle Size and Properties

The particle size of carbon-based colorants is crucial, influencing how the pigment interacts with light, its stability, and its behavior within mediums like the skin. For instance, carbon black particles used in semi-permanent makeup pigments may range from around 100 nm to 500 nm in diameter. Larger particles scatter a broader spectrum of light wavelengths, affecting the perceived color and lightfastness.

Production Methods and Impact

Different production methods for carbon black yield particles with varying sizes and distinct physical and chemical properties.

Channeling. Produces the smallest particles, known as "Channel Black" or "Black 6," from crude oil and gas. These particles, ranging from 90-100 nanometers, contain approximately 19% organic hydrocarbons and 81% inorganic elemental carbon. Characterized by a bluish undertone, they scatter light efficiently at the blue end of the spectrum.
Furnacing. Results in medium-sized particles called "Furnace Black" or "Black 2," created from petroleum oils in a furnace. These 200-300 nanometers particles comprise 55% organic hydrocarbons and 45% inorganic elemental carbon. They have a greenish-anthracite appearance and scatter light across blue to green wavelengths.
Thermal Processing. Creates the largest particles, up to 500 nanometers, known as "Thermal Black" or "Black 7," composed of 1% organic and 99% inorganic elemental carbon. These large particles scatter light across a broad range of wavelengths, resulting in a brownish, warmer skin color that appears less opaque.

Molecule vs. Crystal Lattice of Particles in General

The molecular structure differs significantly from the crystalline structure found in larger particles. While a molecule is a single entity comprised of a specific number of atoms in a precise arrangement, a crystal lattice refers to a repeating pattern of atoms, ions, or molecules extending throughout the material. This crystal lattice structure influences many macroscopic properties of the material, such as color reflection and lightfastness.

Turbostratic or Paracrystalline Structure in Carbon Particles

In pigments like carbon black, we distinguish between the original organic substances' molecular structure and the resulting particles' complex arrangements. These carbon black particles often exhibit a turbostratic or paracrystalline structure, where carbon atoms are restructured into nano-scale aggregates, forming the particles dispersed in pigment formulations. Their structure and arrangement, often less ordered than a true crystal lattice, play a vital role in defining the particles' properties like color, light absorption, and lightfastness. Depending on the manufacturing process, these carbon particles can form various colloidal structures and are typically too large to be soluble, existing as microscopic spheroidal agglomerates.

Analogy to an Onion

The structure of some carbon black pigments can be likened to an onion, with each 'node' or molecule representing a point within the peel-like layers. However, these layers are disordered and spherical, forming the overall particle. This analogy simplifies the concept of layered structures in carbon black particles.

Forces Inside Particles

In carbon black particles, the arrangement of carbon atom 'sheets' or layers is mainly held together by van der Waals forces, weaker than covalent bonds. Production methods can affect the degree of crystallinity and bond types within the particle. In some carbon black forms, regions where covalent bonds link atoms within the sheets while van der Waals forces hold the sheets together. Additionally, some methods can introduce defects or functional groups, leading to interactions like hydrogen bonding or ionic interactions, though these are less common in carbon black particles.

The particle bonding and structure diversity contribute to carbon black pigments' varied physical and chemical properties.

Color Reflection Differences

General reflection properties vary with particle size.

Small Particles (90-100 nm): Comparable in size to the wavelengths of violet and blue light, leading to Mie scattering that gives them a bluish hue.
Medium Particles (200-300 nm): Interact with a broader range of wavelengths, affecting how colors like green and blue are scattered, potentially imparting a greenish hue.
Large Particles (500 nm and larger): Affect light similarly to bulk materials, absorbing various wavelengths and scattering violet and red light, resulting in a brownish appearance.

6. Degradation and Lightfastness

Regarding the degradation of particles and their lightfastness, research indicates that larger, more aggregated particles tend to be more lightfast. As particle size increases, the fading rate due to light exposure decreases. For large particles, the fading rate correlates with the reciprocal of the particle radius (1/a^2), but as particles become smaller, the relationship shifts toward a 1/a dependence. With very small particles, the fading rate becomes less dependent on size.

Photon Interactions

When UV light, composed of photons, strikes a pigment particle, the energy of the photons is either absorbed, scattered, or transmitted. The fate of these photons primarily depends on the size of the pigment particles and the wavelength of the incident light.

Large Particles and Lightfastness

Larger pigment particles tend to exhibit better lightfastness, the ability of a substance to retain its color when exposed to light over time. Several factors contribute to this.

Energy Distribution. Larger particles have a greater volume to distribute the energy they absorb from photons. Like a boulder hit by a sledgehammer, the larger mass absorbs the energy and disperses it, often as non-destructive thermal energy (heat). This dispersion prevents significant structural changes to the pigment molecule.
Scattering Efficiency. The scattering of light by a particle is influenced by its size relative to the wavelength of the light. Larger particles are more effective at scattering light, including UV light, across a broader spectrum. Less energy is absorbed at any given point on the particle's surface, reducing photo-induced degradation.
Surface Area-to-Volume Ratio. Larger particles have a smaller surface area-to-volume ratio than smaller particles, meaning there is less surface area for light to interact with relative to the material available to absorb and dissipate energy.
Resonance Effects. Larger particles are less prone to resonance effects, which can enhance light absorption in smaller particles, leading to more energetic interactions that may break chemical bonds and cause degradation.

Smaller Particles and Increased Reactivity

Conversely, smaller particles have less material to absorb the energy of incoming photons. They are more like fine targets that can be more easily "crushed" or degraded when hit by energetic photons. The energy delivered by the photons can readily break chemical bonds, especially if the particle size resonates with the UV light's wavelength, leading to photochemical reactions that alter the pigment's structure and color, decreasing its lightfastness.

Reactions with Absorbed Wavelengths of Light

When a pigment particle absorbs light, the energy can transfer to the electrons within the pigment, exciting them to a higher energy state and potentially altering the pigment's structure. The likelihood of this photo-induced degradation is influenced by the pigment's chemical structure, bond types, and particle size. Smaller particles are more likely to absorb light energy within their resonant frequencies, leading to significant interactions and potential degradation.

The relationship between particle size, light absorption, and lightfastness is complex and integral to understanding the stability of pigments under light exposure. Particle size directly affects the wavelength range absorbed, thus determining which photonic reactions are more likely to occur. Smaller particles tend to have lower lightfastness because of the following.

They have a larger surface area relative to their volume, allowing for more interaction with light.

They absorb more wavelengths of light and reflect fewer, leading to more photonic reactions.

7. Molecular Stability and Particle Size

Carbon-based particles, frequently used as pigments, are stable from the robust carbon-carbon (C-C) and carbon-hydrogen (C-H) bonds. Known for their strength and resistance to enzymatic breakdown in the skin, these bonds are a primary reason why certain pigment particles, especially those made of carbon or hydrocarbon compounds, remain in the skin post-implantation.

Phagocytosis and Particle Size

Their size significantly affects the immune system's response to foreign particles like pigments. Macrophages are more likely to engulf larger particles exceeding 0.5 micrometers. Conversely, smaller particles under 200 nanometers may evade macrophages due to their reduced efficiency at such sizes, allowing these smaller particles to persist longer in the dermal layer than larger ones, which immune cells more readily clear.

Compatibility with Skin's Lipid Matrix

The solubility of pigment particles in the skin's lipid matrix influences their integration. Particles with a higher organic hydrocarbon percentage, like "Furnace Black" (Black 2), which can contain up to 55% organic hydrocarbons, integrate more easily into the lipid-rich skin, reducing the likelihood of encapsulation or elimination by the body's defenses, leading to more enduring pigmentation.

pH Levels and Particle Size

The pH level of pigment particles can affect their skin interaction. Smaller, nanoscale particles often have more alkaline pH levels, potentially less compatible with the skin's slightly acidic environment. Conversely, larger particles, typically in the 200-300 nm range, tend to have more acidic properties, aligning better with the skin's natural pH, potentially resulting in improved retention and easier implantation.

Empirical Observations

Empirical evidence suggests particle size influences implantation ease. For instance, "Furnace Black" (Black 2), with its larger particles and higher hydrocarbon content, is easier to implant than "Channel Black" (Black 6), which has smaller particles. This ease could result from better skin pH compatibility, natural lipid matrix integration, and reduced phagocytosis for larger particles.

Covalent Bonds of Particles

These strong bonds form the carbon sheets and structures, like graphene layers, composing individual particles. In contrast, the bonds between particles in an aggregate are typically weaker van der Waals forces.

Thus, pigment particle size determines stability and resistance to degradation and significantly impacts interaction with biological systems within the skin. This includes immune responses like phagocytosis, integration into the lipid matrix, skin pH compatibility, and overall ease of implantation. Understanding these aspects is vital for selecting and applying pigments in semi-permanent makeup and other dermatological applications.

8. Aggregates

Difference from Particles in Pigments

The distinction between particles and aggregates primarily concerns scale and interaction in pigments. Particles are the primary pigment units, consisting of a small molecule cluster or a single crystal structure. In contrast, aggregates are clusters of these particles bonded together.

Comparison of Particles

These are the smallest discrete units that retain the pigment's properties. For instance, a particle is a carbon atom arrangement in a particular structure in carbon black. These range from nanometers to micrometers and are the pigment's fundamental “building blocks.”

Aggregate Properties

When particles cluster through physical interactions, they form aggregates. These structures are held together by forces weaker than the chemical bonds within individual particles. In carbon black, these aggregates form when primary particles experience van der Waals forces.

Van der Waals Forces

These are often much weaker than covalent bonds, arising from transient electric dipoles occurring when electrons within an atom or molecule are unevenly distributed. In carbon black, van der Waals forces between particles lead to aggregate formation. These forces keep particles together loosely but are much weaker than the covalent bonds within the particles. The aggregates can influence the pigment's physical properties, like color intensity and dispersibility.

The conditions of pigment manufacturing can influence aggregation and affect the pigment's final properties, like color strength, dispersion ability, and stability. In applications like semi-permanent makeup, the aggregation degree can impact pigment interaction with biological tissues.

Strengths of Bonds in Carbon Black

Strong covalent bonds bond carbon atoms within a single carbon black particle. These robust bonds, where atoms share electrons, provide significant stability to the particle's structure. In contrast, the forces within aggregates are non-covalent and arise due to transient electric dipole moments when electrons within molecules or particles are unevenly distributed. These can happen in carbon black aggregates when particles come close enough for these forces to become significant. Although they can resist some mechanical stress, they are generally weak compared to the covalent bonds within the particles. However, under various conditions, such as when dispersed in a medium, these aggregates can break apart into individual particles.

Understanding the Hierarchy of the Breakdown of Pigment

The decomposition of pigment within the skin generally follows a hierarchical breakdown. Initially, agglomerates, clusters of aggregates, may disassemble into their constituent aggregates. These aggregates, collections of smaller particles bound primarily by van der Waals forces, are weaker than the covalent bonds within the particles.

The subsequent disintegration of these aggregates into individual particles is typically more challenging, as the particles are stabilized by stronger covalent bonds between atoms within the carbon black's crystalline or paracrystalline structure. The integrity of the individual molecules within these particles is even more robust, making them less susceptible to degradation.

As for the atoms within the molecules, they are the most stable and least likely to decompose. The atomic structure, protected by strong covalent bonds, is generally unaffected by enzymatic activity, UV exposure, or immune responses like phagocytosis that might disrupt the larger pigment structures. Decomposition at the atomic level, such as splitting or altering protons and neutrons within an atom's nucleus, does not occur under normal biological conditions in the skin.

Additional observation What should be taken into account, always, are the idiosyncratic properties of concrete substances. Although Van der Waal forces are generally weaker than covalent bonds, they still can be relatively stable. For example, in some carbon black versions, those can only be demolished with fracturing, which in practical terms means laser.

9. Pigment Droplet

Human Eye and Visibility

The human eye can typically discern objects down to about 0.1 millimeters (100 micrometers) under normal lighting. Pigment particles and aggregates within a pigment droplet are significantly smaller, usually in the order of nanometers to a few micrometers. This means the individual particles and aggregates in a pigment suspension are thousands of times smaller than we can see unaided.

Composition of a Pigment Droplet

A droplet of pigment is a complex mixture, including colorant particles, aggregates, and various additives.

Solvents. Liquids that dissolve materials help to keep the colorant in a liquid state for application.
Binders. Substances that provide adhesion, helping pigment particles stick to the surface.
Fillers. Materials added to increase volume or modify properties like texture or consistency.
Preservatives. Chemicals are used to extend shelf life by preventing microbial growth.

These additives can influence viscosity, drying time, and interaction with the skin or other surfaces.

Titanium Dioxide (TiO2) and Lightfastness

Titanium dioxide's inclusion in a pigment formulation significantly impacts lightfastness. TiO2, known for its high refractive index and UV reflection capabilities, can scatter and reflect UV light in a pigment droplet. This can enhance photonic reactions, leading to the degradation of other pigment components. Understanding TiO2's interaction with other pigment components, especially under UV light, is crucial for manufacturers, particularly for products like semi-permanent makeup exposed to light.

Collective Behavior of Variables

The pigment droplet is the first level where the collective behavior of the pigment system is observable to the naked eye. This macro-level view includes all components' physical and chemical interactions, which can significantly differ from the properties of individual particles or aggregates at the micro or nanoscale. Understanding these interactions is critical for predicting pigments' performance and stability in their intended applications.

Healthy Skepticism

Artists should maintain a critical view of product labels and marketing narratives. Promotional messages often oversimplify the nuanced realities of relevant scientific disciplines. Claims conflating the properties of elemental molecules with larger particles or asserting visibility of tiny particles without magnification defy the capabilities of the unaided human eye.

Moreover, complex immunological processes like phagocytosis are sometimes oversimplified, leading to misleading and sometimes scientifically contradictory interpretations. No universal consensus exists among scientists on some of these processes; “exceptions" presented in promotional materials might be scientifically untenable.

Professional artists must approach these topics with skepticism and a commitment to understanding the scientific principles of their craft. Misinformation can lead to misconceptions and impact procedure quality and safety. Artists should seek knowledge through credible sources and continuous education, ensuring their practices align with evidence-based findings in pigmentology and dermatology.

10. The “Lego”-analogy

Chemists and cellular biologists often use analogies to clarify complex concepts. Here's another iteration to underscore the relationships between atoms, molecules, and particles in pigments.

Elements as "Lego" Blocks

Elements are the foundational units of matter, akin to Lego blocks. Like a unique Lego piece, each element has distinct properties determining its interactions with other elements. In chemistry, these interactions are governed by atomic properties, like the number of protons and the electron configuration, influencing an atom's reactivity. For instance, Carbon and Hydrogen can be envisioned as different types of Lego pieces, each with its own shape and form.

Molecules as Assembled Lego Pieces

Molecules resemble several Lego pieces connected to form a particular shape or structure. Each molecule is a specific combination of elements (Lego pieces) bonded in a precise arrangement. Like the shape and functionality of a Lego construct are defined by how the blocks connect, a molecule's properties — such as color, reactivity, and physical attributes — are determined by the types and arrangements of its constituent atoms. It's like snapping together certain pieces to build something more complex.

Particles as Complex Lego Structures

Particles can be likened to larger, more intricate Lego structures comprising multiple connected shapes (molecules). These structures might contain thousands of individual Lego pieces (atoms) organized into substructures (molecules). The arrangement of these substructures contributes to various repeating patterns across the particle, influencing its robustness and properties like light reflection, which gives a pigment its color.

In pigments, particles with the same Color Index code can have vastly different properties because they might be constructed differently at the molecular level, similar to different Lego structures made with the same blocks but arranged in unique patterns or designs. The manufacturing process can also alter these particles, akin to how the stability and appearance of a Lego structure can change based on assembly techniques.

Some structures might have initially snapped-together pieces that are later disassembled or modified, while others use these pieces as is. Similarly, certain structures might leave some pieces unused.

These pigment particles' aesthetic and structural integrity is comparable to masterful Lego creations, where repeating patterns form visually appealing and structurally sound objects.

11. Conclusion

Multi-level Analysis of Pigment Properties

In analyzing pigments used in various applications, including semi-permanent makeup, it's crucial to consider multiple levels of structure, each contributing to the pigment's overall behavior and properties.

Atoms

Atoms are the fundamental building blocks of matter, consisting of a nucleus surrounded by electrons. They form the basic units of elements and define the primary characteristics of any substance.

Molecule

As Molecules are formed when two or more atoms are chemically bonded together. They represent the smallest units of a compound that exhibit its unique chemical properties. Molecules determine many characteristics of a particular compound, such as initial color and reactivity.

Particles

Particles are larger structures comprising many molecules. In pigments, particles often have a crystalline or paracrystalline form, organizing atoms in a structured manner that determines color and optical properties.

Aggregates

Aggregates are clusters of particles bonded by weaker forces like van der Waals interactions. They can influence the pigment's texture, dispersion, and interaction with light.

Droplets

Droplets are the macro-level quantity of pigment visible to the naked eye. They contain pigment particles, aggregates, and substances like solvents, binders, fillers, and preservatives, significantly affecting properties beyond color, such as application ease, drying time, and biological interactions.

Optimal Level of Analysis - Particles (or aggregates)

The particle level is indeed the most informative for evaluating pigment properties. Particles are pivotal in determining attributes such as color intensity, lightfastness, stability, and ease of implantation. They directly affect the pigment's interaction with the skin, influencing perception, behavior during and after application, and how the immune system processes them.

It's important to note that if particles are connected with strong enough bonds to form aggregates, the term "particle" can apply to these aggregates. Therefore, a more accurate statement would be that the optimal level of analysis is at the particle level, which sometimes refers to aggregates of initial spherical particles if the bonds between them are sufficiently robust.

In summary, a comprehensive understanding of pigment behavior necessitates an analysis across all structural levels, primarily focusing on the particle level. At this level, the intrinsic properties defined by atoms and molecules become apparent in a form that directly influences the practical use and longevity of the pigment in applications like semi-permanent makeup. Grasping these structural hierarchies is crucial for professionals in selecting and applying pigments to ensure the desired outcomes are achieved effectively and safely.