In 2010, the global makeup market generated total revenues of US $34.5 billion, with facial makeup including foundations proving the most lucrative at US $12.2 billion or 35.4% of the total makeup market.1 The global market for foundations and concealers alone is expected to grow to US$12 billion by 2014.2 This important product category elicits strong consumer loyalty, meaning that once consumers find the right foundation shade and it performs to their standards, they return for subsequent purchases. This behavior helps a brand to sell its complementary lines and introduce new launches.
Although any formulation type can pose obstacles for the cosmetic chemist, foundations are notorious for their degree of difficulty and intricacy of detail. As if it were not challenging enough to stabilize emulsions with superior aesthetics, foundations require emulsion stability while ensuring color properly develops and stays uniform throughout the product. This involves a balance between the oil and water phase interactions, emulsifiers, film-formers and several powders and pigments. The emulsions that are used to formulate foundations can be o/w and w/o, where silicones are typically used. This article will review the basic factors and common ingredients that comprise foundation formulations.
When developing a foundation shade, the formulator needs to choose the appropriate pigments and pigment levels that can be reliably scaled up to consistently produce the desired color. Pigments are added in the external phase of the emulsion and may need to be altered with a hydrophobic surface treatment, as is the case in w/o foundations. Titanium dioxide and iron oxide are the pigments primarily used in foundations. A wide range of flesh tones can be achieved with rutile or anatase titanium dioxide, using the former for more coverage, along with red, yellow and black iron oxides.
Most cosmetic grade titanium dioxides are coated with alumina or silica to improve photostability. As many color formulators can attest, it is of critical importance to test the light stability of each grade of titanium dioxide in a base formulation before it is completed because even a slight change can have disastrous effects on both light and dark foundation shades over time. For example, a slight yellowing of a pigment will shift the shade of the foundation, which then may not match the shade desired by consumers. Evaluating the light stability of the foundation can be performed by observing it under a UV lamp or sunlight during a determined period.
Processing Pigment Particles
Also important to utilizing pigments in foundations is breaking up large agglomerates to reduce their particle size and make them easier to disperse. This can be accomplished through dry blending or wet grinding, depending on the equipment available and formulators’ preferences. It is generally desirable to fully process the pigments to improve skin feel, minimize cost and maintain shade consistency. Whichever processing method is employed, one must ensure that the same mean particle size is processed to maintain uniform color while avoiding grittiness and streaking.
It is also recommended to incorporate a wetting agent in a foundation formula to aid in the pigment development process. The wetting agent displaces any air surrounding the color particles and ensures that each particle is completely surrounded by liquid. If grinding into water is employed, lecithin or a high-HLB surfactant such as polysorbate 20 will facilitate wetting. When grinding into anhydrous vehicles, look to highly branched esters. Viscosity measurements can also be used to determine optimal wetting materials and levels. A lower viscosity of the resulting mixture correlates with more efficient wetting.
Wetting, which essentially is the velocity at which a liquid penetrates into a powder, can be explained in terms of the Washburn equation, Figure 1. In this equation, h is the height of penetration during the time (t); σ is the surface tension of the wetting liquid; η is the viscosity of the wetting liquid; θ is the wetting angle; r represents the mean radius of the capillaries; C is the structural coefficient, associated with parameters of the porous structure; and W represents energy (heat) of wetting.
Color Intensity and Adjustment
The intensity of the color is another indicator of how well the pigment is processed, and spectrophotometry can be used to measure exact color and intensity. It is particularly useful to benchmark a standard for consistent subsequent batches. Color differences/tint strength can be best quantified by blending in a white base. By maintaining a tight color specification, shade differences will be minimized in production.
However, even with the most strict color specifications, a formulator will need to allow for batch-to-batch color variations necessitating a color match procedure. In other words, a percentage of color (typically 20%) should be left out of the batch so that it can be added incrementally to adjust the product to exactly match the desired shade.
If correctly formulated, the foundation can be adjusted by a skilled color matcher to match the standard shade with just a few color additions. Since the exact amount of color may change with each batch, a quantity sufficient (qs) concentration is required. Each shade should contain an equal ratio of solid to liquid and this is usually accomplished by adding talc, kaolin or other colorless powder fillers to the formula. It is also important to choose a filler with a similar absorption to that of the particular pigments being used to ensure the formula feels the same after any color adjustments are made. The filler is reserved until color matching is completed, at which time a qs amount is added to maintain the solids level.
Some chemists prefer to color-adjust with full formula extenders rather than using pigment dispersion concentrates. A full formula extender is essentially a single color or monochromatic shade of a complete foundation formula. This approach minimizes mistakes and does not require a qs amount since the pigment level is the same for each color.
Sometimes, even though the mass or bottle tone matches the standard, the skin or drawdown does not. This can be due to improper processing or an improperly balanced formula. When matching emulsion formulas, the formulator must account for the degree of whitening created by the base formulation before it is completed. Generally, smaller droplet sizes result in a whiter base. It is imperative that the homogenization shear is carefully monitored to control the degree of base whitening. An experienced color matcher/compounder will look at both mass and skin tone to determine whether to add color or to process more. If the skin tone matches but the bulk tone is darker, this can be corrected with additional high energy mixing in short incremental steps.
Conversely, a matching mass tone but darker skin tone indicates too much whitening from the base emulsion. This can sometimes be remedied with low shear sweep mixing to coalesce droplets, which creates less light scattering in the emulsion.
Stability and Homogeneity
Above all, the stability of a foundation formula is vital. Experiments must be completed to know how the foundation will respond to additional mixing and at different speeds. Creating a stable formula can be a challenge when dealing with colored emulsions. W/O systems have a non-conductive external phase and no stabilizing forces, so use of emulsifiers, waxes and silicone crosspolymers can help to build the structure. Slight changes in the emulsion can also have a large impact on appearance; color striation, flocculation and flotation are common manifestations of instability. Carbomers and polyamide thickeners are particularly sensitive to excess metal ions associated with iron oxides and titanium, so sometimes, the color itself can be the cause of the instability.
Coating the pigments with a surface treatment can mitigate these effects but this is dependent upon the particular formulation. Hydrophobic treatments such as alkyl silane, dimethicone, fluorosilicone and isopropyl titanium triisostearate are particularly useful when formulating w/o systems. These pre-treatments help to ensure that the color remains in the external phase. Oil phase ingredient incompatibility can also lead to striation, so by preparing oil phase blends individually and monitoring them carefully for separation and hazing, this problem can easily be avoided.
To ensure a uniform, homogenous appearance, the color should be dispersed in the external, continuous phase. Since the internal phase is dispersed as droplets, coloring this phase can result in a mottled appearance. Several water-dispersible pigment treatments are commercially available to formulate o/w emulsions, including PEG silicones, lecithin and arabinogalactin. Although it is not as critical to maintain the phase location of pigments in o/w systems, these treatments can decrease processing, lessen mass to skin color differences, and decrease ionic destabilizing effects, as previously described.
Pigment settling is another common occurrence, as pigments are denser than the other ingredients in foundations. Settling is observed when a layer of pigments comes to rest at the bottom of a foundation, leaving a layer of liquid on the top. This separation indicates that the emulsion requires rebalancing to improve its stability, as well as the establishment of a minimum viscosity to maintain this stability. Most liquid formulas will require a “shake well” instruction for consumers. Generally, if the pigments can be remixed by slightly shaking the filled bottle by hand, this is acceptable. If hand mixing is not adequate or is undesirable, a higher viscosity formula may be required. An additional wetting agent and/or emulsifier can also reduce settling.
Hot Pour and Powder Product Types
Hot pour and powder foundations have their own set of formulation challenges. Pigment development is highly process-dependent in anhydrous systems. Wetting and compatibility are important factors. The order of addition, degree of mechanical energy and pour temperature can also greatly affect the color. A consistent color requires a repeatable process, in which all of these factors are carefully monitored and controlled.
Coverage is a key attribute that can vary depending on consumer preference. The base formulation must be carefully calibrated to accommodate the level of pigments required to achieve high, medium or low coverage. In high coverage foundations and concealers, it is important to add the appropriate amounts of oil phase and humectants to avoid a dry, cakey appearance, whereas lower coverage formulas generally require transparent filler ingredients such as talc, silica, sericite, poly(methyl methacrylate), nylon or mica to prevent the pigment from collecting in pores, which creates an uneven, undesired appearance.
Wear is also a major factor that can drive a consumer’s purchase. Wear can be optimized by incorporating film-forming polymers and by choosing the appropriate emulsion system. Most long-wearing formulas are based on volatile w/o systems that dry to a thin layer and resist perspiration and sebum. Siloxane resins, acrylic and PVP-based polymers are often incorporated to improve wear. The oil, polymer and volatile ratios must be carefully balanced to create the desired finish with good wear characteristics.
As noted, the makeup must also resist the negative effects that sebum and perspiration can have on the color and finish. Again, the types of oils/emollients must be balanced against the colors to maintain a consistent shade and finish for several hours. Oil breakthrough from excess sebum can result in dark, unsightly patches. It is therefore advantageous to add absorbent silica or nylon to prevent darkening from sebum. Rigorous panel testing in a variety of atmospheric conditions relevant to the target market is the best way to ensure that the formula has acceptable wear properties.
Although there are many variables to formulating an efficacious foundation, it is important to first identify the main benefits desired. These can be moisturization, durable wear or sun protection. The range of materials a formulator can use is dependent on these benefits. For example, higher molecular weight esters and humectants will allow for a moisturizing foundation but a volatile low viscosity ester provides slip and silky aesthetics.5 Different aesthetics also will be observed when using an o/w versus a w/s system. Choosing the right system and ingredients is the first step to developing what the market desires, and may lessen the problems that arise in formulations.
- Global Make-Up, MarketLine (Nov 14, 2011), www.marketresearch.com/marketLine-v3883/global-6714590/ (Accessed Jan 24, 2012)
- Passport Colour Cosmetics Global, Euromonitor, March 2011, www.euromonitor.com/passport-colour-cosmetics-global/passport-subscription (Accessed Jan 19, 2012)
- LR Fisher and PD Lark, An experimental study of the Washburn equation for liquid flow in very fine capillaries, J Colloid Interface Sci 69(3) 486–492 (May 1979)
- EW Washburn, The dynamics of capillary flow, Physical Review 17(3) 273 (1921)
- J Hollenberg, Color cosmetics, ch 26 in Harry’s Cosmeticology, 8th edn, RG Harry and MD Rieger, eds, Chemical Publishing Co Inc: Gloucester, Mass., USA (2000) pp 531–539