What is the most stable pigment?
Defining two key terms:
PIGMENT – Typically a solid, dry, finely powdered chemical substance used to impart color to paint.
PAINT – A mixture of one or more pigments with a relatively colorless base, which acts as a binder. Paint is the finished product that we use. Creating a specific paint color may require one to ten different pigments.
Each pigment has a unique chemical structure, resulting in individual properties specific to it.
To understand the behavior of paint (especially how it changes over time), it’s essential to know and understand the properties of each pigment within its composition.
Key Properties of Pigments
Stability
Stability is the ability of pigments to retain their initial properties without change. Stability includes:
Color consistency: Retaining the original hue (e.g., red, blue, yellow).
Saturation/brightness consistency: Maintaining the intensity and vividness of the pigment.
All pigments can lose saturation or brightness over time, but the extent of these changes depends on their physical and chemical properties.
When a pigment in paint loses saturation or brightness:
The paint becomes lighter or duller.
The overall tone is affected, which may result in a color shift (inversion) of the entire mixture.
Durability
Durability refers to how long pigments remain visible in the skin, even if their properties partially change.
Example:
A permanent eyebrow tattoo is created with brown paint.
For six months, the paint retains its original brown color.
Over time, the shade shifts: the paint turns gray but remains visible in the skin for a longer period.
The paint is considered durable because the pigment stays in the skin, even though its stability (ability to maintain the original color) is lost.
Relationship Between Stability and Durability
Stability determines how long the paint retains its original color and brightness.
Durability refers to how long the pigment remains in the skin, even if the shade has changed.
Factors Influencing Pigment Stability and Durability
External factors:
UV radiation and heating.
Internal factors:
Oxidation – changes in pH (acid-base balance in the skin).
Immune response – phagocytes attack pigment particles, absorbing and partially destroying them.
Classification of Pigments in PMU Paints
Types of Inorganic Pigments
Inorganic pigments are used in PMU paints due to their high stability, resistance to UV radiation, and low allergenicity.
Iron Oxides:
Black pigment: Fe₃O₄ (magnetite).
Stability: High, with slow changes in intensity over time.
Red pigment: Fe₂O₃ (hematite).
Stability: Very high. One of the most stable pigments due to its chemical inertness.
Yellow pigment: Iron oxide hydroxide.
Stability: High, though less stable in acidic environments compared to other iron oxides.
Carbon Black (C):
Provides a deep, rich black color. Produced via thermal decomposition of organic materials in an oxygen-free environment.
Stability: High. May lose some saturation due to partial pigment removal by the immune system.
Titanium Dioxide (TiO₂):
Used to create white and pastel tones.
Stability: Very high. Retains its color well and resists chemical agents.
Chrome Oxide Green (Cr₂O₃):
Produces green tones.
Stability: High. Resistant to light, moisture, and chemical exposure.
Ultramarine:
A bright blue pigment based on aluminosilicates containing sulfur.
Stability: Moderate. Sensitive to acidic environments, which may affect its saturation.
Types of Organic Pigments
Organic pigments are characterized by high brightness and vividness. They are synthetic dyes deposited on insoluble bases for stability (e.g., calcium or barium sulfates, aluminum hydroxides).
Azo Pigments:
The most popular organic pigments due to their availability and wide color range (from bright reds to yellows). Their production is relatively inexpensive, making them economically advantageous for mass use. Azo pigments are more widespread than quinacridones, phthalocyanines, indolinones, or perylenes.
Examples:
CI Pigment Red 22 (CI 12315)
CI Pigment Yellow 14 (CI 21095)
CI Pigment Orange 13 (CI 21110)
CI Pigment Red 112 (CI 12370)
CI Pigment Brown 25 (CI 12510)
CI Pigment Yellow 74 (CI 11741)
CI Pigment Red 170 (CI 12475)
Stability: Low. Azo pigments are less stable than other organic pigments and are prone to decomposition under UV radiation, oxidation, or pH changes.
Phthalocyanines:
Provide bright blue and green tones. Often used in brow pigments to tone down the brightness of other organic pigments. Banned in Europe from 2023.
Examples:
CI Pigment Blue 15 (CI 74160)
CI Pigment Green 7 (CI 74260)
Stability: High. Resistant to light and chemical exposure.
Quinacridones:
Used to create rich purple, red, and pink tones. In PMU paint production, they are limited to lip pigments due to their high intensity, which may be too strong for natural-looking shades. More expensive than azo pigments.
Examples:
CI Pigment Violet 19 (CI 73900)
CI Pigment Red 122 (CI 73915)
Stability: High. Chemically inert and UV-resistant.
Indolinones:
Known for their high color saturation, used for yellow and orange tones. Less popular than azo or phthalocyanines due to higher costs.
Examples:
CI Pigment Yellow 109 (CI 56280)
CI Pigment Yellow 110 (CI 56285)
Stability: High. Resistant to light and chemical exposure.
Perylenes:
Moderately used for deep red, burgundy, and dark purple tones. Among the most expensive organic pigments due to their complex synthesis.
Examples:
CI Pigment Red 179 (CI 71130)
CI Pigment Red 224 (CI 71102)
Stability: High. UV- and chemically resistant.
Conclusion:
Among inorganic pigments, the most stable are:
Titanium Dioxide (white),
Red Iron Oxide,
Carbon Black.
Among organic pigments, the most stable are:
Red and purple perylenes (CI indexes starting with 71),
Slightly less stable are phthalocyanines (blue and green),
Quinacridones and indolinones (CI indexes 73 and 56).
The least stable, but most widely used, are azo pigments (CI indexes often starting with 12, 21, and 15).
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