4. Types of pigments in tattoo inks

4.1 Inorganic Pigments

Inorganic pigments can be obtained either naturally by grinding minerals or as synthetic products derived from various manufacturing processes. Although there are many different types of pigments in this group, three main types of metal oxides are used in tattooing: titanium oxides, iron oxides, and chromium oxides.

4.1.1 Titanium dioxide

Not all whites are the same. The most important white pigment—and indeed one of the most important pigments in all tattoo inks, whether for permanent makeup, medical tattooing, or traditional tattooing—is titanium dioxide. It has the highest refractive index among white pigments and thus offers the highest opacity and reflectivity of all white pigments. Without white pigment, it would be impossible to classify colored pigments into dark, medium, light, and pastel shades. Likewise, the use of titanium dioxide influences a color’s opacity. Without white, most colored inks would appear translucent and thus matte. Titanium dioxide occurs in three different crystal forms, two of which are of technical significance: anatase and rutile. In the past, anatase was primarily used. Currently, the rutile form of titanium dioxide is increasingly used, as it is less prone to forming free radicals when exposed to sunlight compared to anatase and thus places less stress on the surrounding tissue.

4.1.2 Iron oxides

Another important group of inorganic pigments is iron oxides. They are primarily found as iron oxide red, iron oxide yellow (ochre), iron oxide black, and as a mixture of the three iron oxides in brown. These pigments are very easy to work with and produce natural-looking results. Due to future regulations and the fact that only iron oxide red is stable, iron oxides are increasingly disappearing from the product range as an important pigment class. As previously mentioned, iron oxide pigments tend to shift toward red over time and with temperature, as red iron oxide is the most thermodynamically stable variant. Iron oxide yellow, on the other hand, has another distinctive feature besides the shift to red: due to its needle-like structure, the pigment can shift toward greenish tones when destroyed by fine grinding or through the application of laser treatments.

4.1.3 Chromium oxides

The chromium oxide pigment group is mentioned here for the sake of completeness. It covers the range of green shades. To be precise, there is a chromium oxide green and a chromium oxide hydrate green. These pigments are used—if at all—in permanent makeup as so-called “red stoppers,” i.e., greenish corrective shades for reddish eyebrows.

4.2 Organic Pigments

Organic pigments are artificially produced colorants. While inorganic pigments tend to appear dull and natural and cover a limited color spectrum, organic pigments, with their diversity and brilliance, extend the color spectrum to encompass the entire visible range. This category of pigments can be roughly divided into azo pigments and polycyclic pigments. While azo pigments have the azo group N=N as their characteristic color-forming group and are produced using aromatic amines, phenols, and naphthols, polycyclic pigments have a significantly more complex structure and—depending on the pigment—can be synthesized without problematic aromatic amines. Furthermore, due to their size and structure, polycyclic pigments are more stable and lightfast than azo pigments.

4.3 Pigment Blacks

Colored carbon blacks are the strongest and most important black pigments used in permanent makeup (PMU) and tattoo inks. Depending on the manufacturing process, different particle sizes are obtained, resulting in black tones ranging from reddish-brown to bluish-green. Carbon black is produced by the incomplete combustion of gases and oils and thus consists of carbon.