Persistence of organic pigments (Carbon black)

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1. Background

This article is based on empirical data gathered from interviews with 46 experienced artists who specialize in using organic pigments, including carbon black. These interviews were conducted over four years, from 2019 to 2023. The insights and information obtained have been rigorously reviewed and validated by professionals: two chemists, a dermatologist, and a cellular biology expert. This article contributes to an advanced level of study in pigmentology. It is part of Level 2 in the three-tier framework at the Holistic PMU and Powderbrows.com Research Center. Readers should note that a basic understanding of chemistry and pigmentology is assumed, which is essential for fully grasping the concepts presented here.

2. Understanding Carbon Black

Carbon black is a specially engineered material, mainly composed of elemental carbon. It's created through partial combustion or thermal decomposition of hydrocarbons (organic compounds made of hydrogen and carbon). Carbon black typically forms as aggregates, which are clusters of shapes resembling chains or bunches of grapes. These aggregates consist of tiny, spherical primary particles.

Each of these primary particles is about the same size within a single aggregate, and they are arranged in layers that overlap in a disordered manner, known as turbostratic layers. The size of these particles and the aggregates can vary, depending on the type of carbon black. Although the size range of particles and aggregates may differ in each type, the size of the primary particles within any single aggregate is usually consistent. This consistency in size within each aggregate is a crucial aspect of carbon black's structure. It significantly affects how carbon black behaves and how it can be used in various applications.

3. Primary Particles and Aggregates

In pigmentology, especially when analyzing colorants from a chemical and physical perspective, there's often confusion due to the interchangeable use of terms like "molecule," "particle," and "aggregate." This is particularly true in the case of carbon black (CI 77266), a well-known subject in organic chemistry.

Primary Particle Explained

In the context of carbon black, the term "particle" usually refers to a primary particle, which is spherically shaped. These particles have a paracrystalline, non-discrete structure and vary in size, typically ranging from 25 to 500 nanometers (nm) in diameter, depending on how they are produced. Examining their crystalline structure, including the overlapping turbostratic structure, shows how stable "flakes" formed by strong covalent bonds are held together in a sphere by weaker van der Waals forces.

Aggregate: The Overlooked "True Particle"

An important aspect often overlooked is that these primary particles usually form a larger structure known as a carbon black aggregate. These aggregates, which are about 1 micrometer (1000 nm) in size, can only be separated by fracturing them apart. This points to a crucial fact: despite the presence of primary particles, it's the aggregate – a cluster of these particles – that should be considered the "real particle" in discussions about carbon black in pigments.

Implications for Semi-Permanent Makeup

Understanding that aggregates are the "true" particles in carbon black is significant in semi-permanent makeup. The way these aggregates behave in the skin, their interaction with biological structures, and their color stability are key factors. Recognizing the aggregate as the actual particle allows professionals to adapt their techniques and materials for safer and more effective applications, considering the true behavior of pigments in the skin.

To delve deeper into this topic, let's examine the concept of fracturing, which is necessary for breaking down the aggregate into primary (nano)particles.

4. Fracturing in Carbon Black

Breaking Down Aggregates

Fracturing in the context of pigment particles, such as carbon black, involves breaking down the aggregates into individual primary particles. The aggregates are clusters of primary particles held together by van der Waals forces, which are relatively weak electrostatic attractions. A significant amount of energy is needed to fracture these aggregates and separate them into primary particles. In a laboratory, this can be achieved using mechanical, ultrasonic, or chemical methods, disrupting the aggregate structure and releasing the primary particles.

Fracturing in the Context of Skin

In semi-permanent makeup applications involving human skin, the feasibility of fracturing changes drastically.

The energy level needed to fracture carbon black aggregates in the skin is typically not naturally present. The mechanical forces applied during makeup application are not strong enough to cause fracturing at this level.

Theoretical Implications

Theoretically, fracturing in the skin would require an external force, like ultrasonic treatment. However, such methods are uncommon in cosmetic or dermatological treatments and could be unsafe.

Biological Impact

If fracturing were to occur in the skin, it might increase the exposure of the skin to smaller primary particles. These particles have a higher potential for penetrating the skin and interacting with cells, which could lead to various biological reactions, including inflammation or cellular stress.

Considering the challenges and risks, the stability of pigment aggregates in semi-permanent makeup is beneficial. It ensures a more predictable interaction with the skin and minimizes the risk of unintended biological responses.

Preliminary Conclusions

While fracturing carbon black aggregates into primary particles is scientifically feasible, its practical application in human skin, especially for semi-permanent makeup, is highly unlikely and not recommended due to the potential risks and lack of natural or safe methods. This understanding is essential for semi-permanent makeup professionals to ensure safety and effectiveness.

Fracturing and Laser Removal

Interestingly, fracturing is closely related to laser removal treatments in semi-permanent makeup. This process often breaks down the aggregates, considered the "real particles," in the skin. Many artists are aware of this, as laser treatment is a common method for pigment removal.

5. Laser treatment as fracturing

Overview of Laser Tattoo Removal

Laser tattoo removal employs powerful light pulses to target pigment particles in the skin. The main mechanism is photothermolysis, where the pigment absorbs specific light wavelengths, causing rapid heating and the breakdown of the pigment particles. This can be understood as a form of fracturing.

Selective Absorption and Rapid Heating

The laser precisely targets pigment particles based on their color and absorption properties. Carbon black, a strong absorber of laser light, is particularly affected. The absorbed laser light rapidly heats the carbon black particles, causing them to expand.

Breaking Down Aggregates

This rapid heating and expansion lead to the mechanical breakdown of the carbon black aggregates, effectively fracturing them into smaller fragments. This process is more controlled and localized compared to broader mechanical fracturing methods seen in industrial contexts.

Dispersion and Removal by the Body

Once the aggregates are fractured into smaller particles, they are more easily processed and eliminated by the body's immune system. The lymphatic system then gradually removes these particles, resulting in the fading of semi-permanent makeup or tattoos.

Laser tattoo removal is designed to be precise and safe, targeting pigment particles without significantly damaging surrounding skin tissues. This ensures effective pigment removal with reduced potential side effects.

Preliminary Conclusions

Laser tattoo removal can be seen as a sophisticated, targeted form of fracturing. It uses specific wavelengths of light to induce rapid heating and expansion of pigment particles, breaking them down for removal by the immune system. This method provides a controlled and safe way to alter and eliminate unwanted pigmentation, such as tattoos.

Understanding the scientific causality behind laser removal is crucial for developing a critical approach to simplified explanations, such as carbon black being "broken down by UV light." This often-used explanation by some artists who lack in-depth knowledge needs further exploration. We will explore the possibility of UV light fracturing carbon black aggregates in the skin.

6. UV Light and Stability

High Lightfastness of Carbon Black

Carbon black is renowned for its high lightfastness index, indicating its resistance to fading under light exposure, including ultraviolet (UV) light. This resistance is due to the stable chemical structure of carbon black particles.

Limitations of UV Light in Breaking Down Aggregates

The energy emitted by UV light from the sun is significantly lower than required to fracture carbon black aggregates. While UV light can induce chemical changes in certain materials, it lacks the necessary energy to break the strong bonds within carbon black aggregates. Consequently, expecting UV light to break down these aggregates in the skin significantly is unrealistic.

Enthalpy and Entropy in Carbon Black Aggregates

Enthalpy refers to a system's total heat content or energy, while entropy describes its degree of disorder or randomness.

Stability of Aggregates. A carbon black aggregate, about 1 micrometer in size, is inherently stable. Its enthalpy represents the energy maintaining its structure, and its entropy reflects the arrangement of primary particles within it.
Effect of Rearranging Primary Particles. Shifting the primary particles within an aggregate doesn’t significantly change its enthalpy and entropy. The internal forces, like van der Waals forces, remain relatively constant even if the positions of primary particles vary. This is because the overall structure and energy of the aggregate remain stable despite minor rearrangements.

Analogy: A Bunch of Grapes

Consider a bunch of grapes, each representing a primary particle in a carbon black aggregate.

Stability and Properties. Just like rearranging grapes in a bunch doesn't significantly alter their overall properties (such as weight, volume, or shape), rearranging primary particles in a carbon black aggregate doesn’t fundamentally change its overall properties.
Implications for Stability. This analogy helps explain why minor internal changes within an aggregate don’t lead to significant shifts in behavior or properties. The aggregate remains stable, akin to a bunch of grapes, regardless of the individual positions of its components.

In conclusion, the inherent lightfastness of carbon black makes it resistant to UV light-induced breakdown. The stability of carbon black aggregates is maintained despite internal rearrangement of primary particles. The bunch of grapes analogy effectively illustrates the overall stability of these aggregates.

Next, we will address a common query that puzzles many artists: the claim that smaller carbon black particles are more stable than larger ones. This comparison is often made between different types of carbon black, like Furnace black and Thermal black, in the context of semi-permanent pigments. We'll examine this comparative stability more closely in the following section.

7. Stability of Carbon Black Particles

Surface Activity and Reactivity

The surface activity of carbon black, which determines its chemical reactivity, depends on the arrangement of graphitic planes and the presence of organic side groups.

Molecular Composition

At a molecular level, carbon black comprises amorphous graphite layer planes made from aromatic rings. The edges of these planes have unsatisfied carbon bonds, creating potential sites for chemical reactions.

Production Processes and Structural Differences

Thermal Black Production. The production of thermal black involves prolonged reaction times and high temperatures, around 1300°C. This process produces more orderly graphite layer planes with fewer unsatisfied carbon bonds at the edges. Consequently, there are reduced sites for elastomer interaction, indicating less surface reactivity.
Furnace Black Production. Furnace black is produced with shorter reaction times, leading to less ordered layer planes. This results in more unsatisfied carbon bonds and, therefore, a higher number of reactive sites.

Recent studies using scanning tunneling electron microscopy (STM) reveal that larger particle-size carbon blacks, like thermal black, have a more organized surface structure with fewer active sites. This suggests greater stability and lower reactivity compared to smaller particle-size carbon blacks.

Production Environments and Their Influence

Thermal Black Environment. Thermal black is produced in an environment without flame or air, contributing to its purity and stability.
Furnace Black Environment. Furnace black is typically made through the incomplete combustion of petroleum residues and contains various organic functional groups. These groups increase their surface activity and potential reactivity.

Preliminary Conclusions

Based on these observations, thermal black (Black 7) exhibits greater stability and lower reactivity than furnace black (Black 2). Its larger particle size, more organized surface structure, and lack of reactive organic functional groups make it a more stable option. This is particularly important in applications where stability and reduced reactivity are critical, such as in semi-permanent makeup.

8. Conclusions

The Aggregate as the Fundamental Unit

In semi-permanent makeup, it's essential to recognize that the aggregate, not the primary particle, should be considered the "true particle" in discussions about carbon black. These aggregates, clusters of primary particles, significantly influence the behavior of pigments in the skin, their interaction with biological structures, and their stability and color properties. Understanding the aggregate as the basic unit in pigment analysis enables professionals to refine their techniques and materials for safer and more effective applications.

Fracturing of Aggregates: Practical Considerations

Scientifically, fracturing carbon black aggregates into primary particles is a valid concept. However, this process is neither practical nor advisable in the context of human skin, especially in semi-permanent makeup. The risks and lack of natural or safe methods for such fracturing highlight the need for professionals to be aware of these limitations to ensure safe application practices.

Laser Removal: A Specialized Fracturing Technique

Laser tattoo removal can be viewed as a controlled fracturing method, efficiently targeting and breaking down pigment aggregates like carbon black. Utilizing specific light wavelengths induces rapid heating and expansion of the pigment particles, aiding their removal by the body's immune system. This method's precision offers a safe and focused way of eliminating unwanted pigmentation.

Carbon Black's Resistance to UV Light

Carbon black is characterized by high lightfastness, making it resistant to breakdown by UV light. The aggregate's stability is maintained even when its primary particles are rearranged. This concept is well-exemplified by the analogy of a bunch of grapes, where changing the position of individual grapes doesn't significantly affect the bunch's overall properties.

Superiority of Thermal Black in Stabili

ty Thermal black (Black 7) exhibits greater stability and lower reactivity with its larger primary particles than furnace black (Black 2). Factors like larger particle size, more organized surface structure, and the absence of reactive organic groups make thermal black particularly suitable for uses where stability and reduced reactivity are paramount, such as in semi-permanent makeup.