The U.S. Food and Drug Administration has the authority to regulate tattoo ink and the pigments it contains, but the agency rarely exercises this oversight. As a result, most manufacturers decline to reveal the ingredients in tattoo ink, which they consider a trade secret. Fortunately, scientific analyses have identified many common ingredients in tattoo ink of various colors. According to the Dr. Tattoff website, brown tattoo ink derives its color from ochre, a traditional mineral pigment that includes a mixture of clay and iron oxide.
Carrier Solution
In addition to a pigment that provides color, tattoo ink contains a liquid carrier solution. The solid pigment particles are suspended in this solution to create an even color and enable tattoo artists to inject the color beneath the skin. The Healthy Skin Association lists several substances widely used in carrier solutions, including ethyl alcohol, propylene glycol, witch hazel, Listerine and purified water. These substances are popular because they tend to reduce the risk of contamination or infection.
Iron Oxide
According to the Minerals Zone website, ochre derives its color primarily from iron oxide. Ochre can vary from deep red to brown or yellow and can also have gray or green tones. The exact hue of a given sample of ochre depends on the amount of iron oxide and whether the iron oxide is hydrous, or bonded with water. Red ochre has the most iron oxide, while shades such as sienna, umber, and yellow and brown ochre have less iron oxide and may include other colorful minerals.
Clay
While iron oxide, water and other trace minerals determine ochre's color, the bulk of its substance consists of clay. The Minerals Zone site explains that raw ochre is traditionally refined by crushing it and washing it with a solvent to extract the rich pigment from the dull clay. This process is known as leaching or lixiviation. After refining the pigment further through additional rinsing, the resulting substance can be dried or heated to create a deep, stable and pure pigment for use in ink.
Silica
Silica, or silicon dioxide, is abundant in nature in forms such as quartz and sand. Silica is a common component in raw ochre and can affect the color and composition of the unrefined material, according to the Minerals Zone site. When ochre is processed and refined to produce pigments of various colors, most of the silica is removed. However, refined ochre will still contain trace amounts of clay and silica, as will inks and other products incorporating ochre.
Water
In addition to the amount of iron oxide in ochre, water content plays a significant role in determining color. According to the Minerals Zone website, hydrous iron oxide, which has bonded with water, tends to be yellow, whereas anhydrous iron oxide is a deep red. When ochre contains more or dryer iron oxide, it tends to be red. When iron oxide is less prevalent or heavily hydrated, ochre has a yellow or brown color.
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