SKIN CARE 45
Pigment primer for the skin care formulator
n Kelly A Dobos, Anthony J Rohrer – Sun Chemical, US
Traditional foundation and face powder makeup are an important part of the consumer’s beauty routine and several new trends are contributing to the rise in number and type of cosmetics available for the face.
The ‘alphabet cream’ trend has resulted in the development of BB creams (followed by CC, DD and EE), which have the colour correction properties of foundation and a multitude of other benefits from ingredients like sunscreens, antioxidants and botanicals. Due to the blurring of these lines between skin care and colour cosmetics, skin care formulators need to develop a solid understanding of the unique nature of pigment chemistry and processing to achieve consistent colour in production and maximise the value of colourants.
Typical pigments used in matching skin tones
Much like foundation, the typical pigments used to create various skin tones in ‘alphabet creams’ are inorganic oxides (titanium dioxide, yellow iron oxide, red iron oxide and black iron oxide). Lake pigments are not typically used in products for face makeup as their chemical and physical properties differ greatly from oxides and their colours are often too bright to mimic skin tones.1 Rutile and anatase forms of titanium dioxide can be used. The rutile form provides a higher degree of coverage for hiding blemishes and imperfections. Titanium dioxide is available in oil soluble, water soluble, and multipurpose grades. Selection depends on the nature of the continuous phase of the desired emulsion. Silica or alumina are used to coat cosmetic grades of titanium dioxide to improve photostability.2 Iron oxides are in many ways ideal pigments with regard to stability. However, processing temperatures in the range of 125 – 150 °C yellow (Fe2 iron oxides (Fe3
O3 O4 shade. Red iron oxide (Fe2 •H2
) can shift to a more red O3
O) and black ) is made by
calcination of yellow iron oxide at very high temperatures and is quite stable with respect to heat. Additionally, black iron oxide is slightly
November 2017
magnetic and will coat iron or mild steel containers resulting in issues with colour development during manufacture. Iron oxides are also available as blends described as brown, russet (reddish-brown), tan, etc. Blended iron oxides reduce formulation and processing time to develop finished shades of product.3
Occasionally ultramarine blue is used to aid in achieving darker skin tones as long as the pH is above 7, otherwise it decomposes and gives off an unpleasant hydrogen sulfide gas.3
Pigment standards and quality control
When selecting pigments for use in formulation it is important to evaluate multiple lots of material from the supplier, including the designated standard lot. The supplier’s standard lot should always be used for quality control in comparing receipt of new lots of pigment. Additionally, due to the presence of agglomerates and aggregates discussed in further detail later, colour quality evaluations must be performed in dispersion. Subjective visual evaluations of colour can be made under a controlled light source. However, objective measurements read on a colour computer are far more reliable. As the formulations and compositions of
base formulas vary widely between end users or pigments, internal tests can be developed by manufacturers to better understand and prepare for shade adjustments in production.
Pigment dispersion Classical cosmetic pigments are made in large batches and there are unavoidable, slight variations in shade or other qualities from batch to batch. Pigments are typically supplied as dry powders where primary particles exist in various states of aggregation and agglomeration that often amplify the variation in colour properties when evaluated as dry powders. Pigments must be fully extended or dispersed in a vehicle to get as close as possible to primary particle size in order to see the full development of colour and maximise financial value. Dispersion is the process of wetting, separating and distributing pigment particles in a vehicle. Additionally, the particle must be stabilised against flocculation and settling. Separation of pigment particles requires intense energy input by specialised equipment like a 3-roll mill for liquids or use of a pulveriser for powders. Ensuring a reproducible mean particle size through dispersion is crucial to achieving uniform colour while avoiding streaking and grittiness.2,3
PERSONAL CARE ASIA PACIFIC
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