Article by: Kelly Dobos
Classical cosmetic pigments are made in large batches so there are unavoidable, slight variations in shade or other quality from batch to batch. The pigments are supplied as dry powders where primary particles exist in various states of aggregation and agglomeration that amplify the variation in color properties when evaluated as dry powders. These pigments must be fully extended or dispersed in a vehicle to get as close as possible to primary particle size to see the full development of color.
Dispersion is the process of wetting, separating and distributing pigment particles in a medium. It requires intense energy input through high sheering in liquids or pulverization in powders. It can also require specialized equipment.
Quality Controls of Colorants
Things to consider when creating standards
- Evaluate at least three lots of material from the supplier including the designated standard lot. It is important to note differences in synthesis, substrate, and composition can cause variation in color space between suppliers so they are rarely drop-in replacements and should be evaluated independently.
- You and your supplier should understand and agree on specifications, standard, and test methods presented by the supplier.
- Ensure product development is performed with material that is representative of the supplier’s product capabilities. Selecting a lot for development work that is at the edge specifications can be problematic.
Your light source for evaluation must be specified and controlled.
- Dyes: Visual and spectrophotometric evaluation in solution.
- Pigments: Pigment cannot be evaluated as received in dry pigment form because the degree of aggregation and agglomeration varies from batch to batch. Wet dry dispersions (depending on the end application) are prepared under defined conditions and to a defined level of dispersion.
As the formulations and compositions of base formulas varies widely between end users or pigments, internal tests can be developed to better understand and prepare for shade adjustments in production as it would be impractical for the supplier to develop a quality method for every possible customer.