24 LIFESTYLE COSMETICS


Additive colour mixing


Pigment Pigments are those colour additives that are not soluble in the medium in which they are used. The difference between dyes and pigments is not always clearly delineated as colourant that is a dye in one medium may behave like a pigment in another.


Pearlescent pigments Insoluble colour additives that impart an iridescent and sometimes sparkling look depending on particle size.


Colour theory and principles of colour mixing Additive colouring is what happens when you mix colours of light together. Mixing all colours of light produces white light. Subtractive colour mixing is what


happens when you mix pigments together. In subtractive mixing, every addition of a new colour brings the result closer to black, reflecting less light consequently subtractive is used as a descriptor. While colour printing machines use cyan,


magenta, yellow and key (black) subtractive colour mixing, we can consider the primary colours to be red, yellow, and blue for cosmetic pigments. Primary colours cannot be mixed or formed by any combination of other colours but all other colours can be derived from these three hues. Primary colours are sometimes described


as pure colours, though it is important to keep in mind that cosmetic colour additives are rarely pure colours. Small amounts of other colours are visibly in each pigment and this gives each pigment a colour bias. Red 7 Lake, for example, is a blue-shade of red while Red 6 Lake is a yellow shade of red. When mixing colours, these biases need to be considered. Mixing pigment colours with white, black and shades of gray changes the value of a colour. Value is the relative lightness or darkness of a colour. A tint is created when white is added to a hue or pure colour. Tints are lighter and less intense than the


PERSONAL CARE January 2024


Subtractive colour mixing


original colour, the resulting shades are softer hues like pastels. A shade is created when black is added to a hue or pure colour. The resulting colours are darker than the original and often have a more intense, richer quality to them. Lastly, a tone is created when gray is added to a pure hue or colour. These colours will appear darker than the original hue used, but the overall value or brightness will be reduced.


Working with dyes Dyes are typically used low levels and provide transparent colour. Dyes are most commonly used in personal care products and toiletries but they do find some use in decorative cosmetics as well. The fluorescein dyes (D&C Orange 5,


D&C Red 21, and D&C Red 27) are used in conjunction with pigments to produce long- wear lipsticks due to their staining properties, which give the impression of longer wear. These colour additives behave as pH indicators and are also used in colour-changing blush and lip products. A dye stock solution is a solution of dye


powder dissolved in a solvent, typically water. Working with dye stock solutions is safer, cleaner, more accurate, and more convenient than working with dye powders in the laboratory.


The amount of dye powder dissolved in a specific volume of water determines the strength of the solution, expressed as a percentage by weight of dye powder to the total weight of the dye stock solution. Using the metric system, 1 millilitre (ml) of water weighs 1 gram, so a 1.0% dye stock solution contains 1 gram of dye for every 99 ml of water. Distilled or deionized water should be


utilized when preparing aqueous stock solutions. Calcium and magnesium ions in hard water can form insoluble salts of dyes that will cause sediment. Depending on the solubility of the dyes


and composition of the product in which you plan to use dye stock solutions there may


be other useful solvents besides water like glycerin, glycols, or ethanol. Water-based stock solutions should be used quickly or preserved to prevent microbial growth. With emulsions, the use of water soluble


or oil soluble colour will depend on the continuous phase. Water soluble dyes would be used in an oil-in-water (O/W) emulsion and oil soluble dyes in a water-in-oil (W/O) emulsion. Many of the natural or nature identical


colourants permitted for use in cosmetics and personal care products behave as dyes. Synthetic dyes are typically more stable compared to natural or nature identical dyes but all colourants should be stored in a way that minimizes exposure to heat and light. UV absorbers can be incorporated into the


product or packaging to improve light stability. A good technical data sheet from a colourant supplier will include relevant information about incompatibilities and stability concerns. Most dyes have good colour strength and


are used at concentrations of 0.015% (150 ppm) or less depending on the desired hue. The use of higher levels of dyes in products is often avoided as it can result in staining of skin, towels or clothing.


Classical pigments Classical cosmetic pigments are used in makeup products to provide opacity and colour payoff. Payoff refers to the amount colour a product delivers on the desired substrate. Payoff can be assessed by the saturation and opacity of the pigment film laid down.


Pigments may be insoluble due to their


chemistry, such as iron oxides and Red 36 (CI). Others are created by adsorbing a soluble dye onto an insoluble substrate creating a lake. Classical pigments are made in large


batches and there are unaidable, slight variations in shade or other qualities from batch to batch. The pigments are typically supplied as dry powders where primary particles exist in various states of aggregation


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