There have been many articles written on pigment dispersion across various publications over the years, the vast majority of which have been very theoretical in nature, using mathematical equations accompanied by graphs and charts to reinforce a given author’s particular points of examination or contention. Unfortunately, they have also tended to be generic in nature with respect to the end use applications for which the dispersions are intended.
"Pigment Dispersion," chapter 6 of Coloring the Cosmetic World: Using Pigments in Decorative Cosmetic Formulations, will not repeat the mathematics and graphs, but rather it will concentrate on the practical aspects of making quality dispersions of pigment, focusing on the techniques and equipment commonly used in the decorative cosmetic industry. In nearly all cases, images of the equipment will accompany the discussion, in order to give the reader a method to visualize the physical process itself.
The Importance of Dispersion
Dispersion is the most important process for incorporating pigments into decorative cosmetics. Though this importance has been alluded to earlier in Coloring the Cosmetic World: Using Pigments in Decorative Cosmetic Formulations, those allusions were brief, and before we can now (finally!) begin a study of the dispersion process, it is necessary to define exactly what dispersion is—to secure a working definition of it that will see through the review to follow. But rather than one, there are two definitions that will be presented here.
The first is a descriptive definition that gets to the heart of what dispersion is all about and the second addresses the technical aspects of the process itself. A pigment, when received by a cosmetic company, is in a highly aggregated, agglomerated state that is of little color or money value.
So, addressing this issue, the first definition of dispersion is as follows: Dispersion is the process that converts a “raw” pigment into a usable form, providing the best color and money values. The second, and more technical definition, is: Dispersion is the process of wetting, separating and distributing particles in a vehicle.
Figure 1 (D&C Red 7 Ca Lake) and Figure 2 (Ferric Ammonium Ferrocynanide) illustrate clearly what dispersion does and why it adds tremendous value to the pigment.
The two images on the left of each display are masstone, meaning that they are prepared with two components–pigment and castor oil. The ones on the right side of each display are tints–prepared by diluting the masstones with zinc oxide. The masstone contains two individual components–the one on the left is made by simply mixing the pigments with castor oil using a spatula, while the one on the right is made by properly dispersing the color into the castor oil. It is easy to see visually the impact dispersion makes on the color.
It is plain to see that the masstones of the mixed preparations are very light and opaque when compared to the dispersed ones. Likewise, the strength of the mixed preparations is extremely weak versus the dispersed ones. Gloss is an important property of lipsticks, lip glosses and nail polish. Their ability to provide shine on the skin is an important property to the appeal of the cosmetic. Improperly dispersed pigments result in more diffuse reflection, which yields a dull finish on the skin. In addition, liquid cosmetic products must exhibit acceptable viscosity and flow properties, commonly called rheology, in order for these products to be easily removed from their container and apply smoothly onto the skin. Improperly dispersed pigments contain large particles that interfere with the rheology of the product, making it difficult to apply to the skin and rub off easily, forcing the consumer to re-apply the product more frequently.
This information is an excerpt from the book Coloring the Cosmetic World: Using Pigments in Decorative Cosmetic Formulations. To learn more about this topic or to purchase the entire book, visit www.Alluredbooks.com.
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