colorants, Lochhead and a graduate
student, Laura Anderson, found that scientists are developing composite makeup
particles that diffract, refract and reflect
light off the wearer’s skin, rather than
covering the skin with an opaque barrier.
Not only do these particles let the natural skin color pass through to the outside
world—albeit with enough blurring to
hide small surface imperfections—but
they can even produce new hints of color
for a radiant glow.
The diagram below illustrates what
happens when light hits one of these
coated mineral particles, shown in
cross-section. According to Morante,
the particles—which are no larger than
10 µm in diameter for optimum feel
and performance in the makeup—
scatter light away from the eye so that the
small wrinkles aren’t apparent.
Some foundations, according to
Lochhead, contain tiny alumina platelets, some treated with metal oxides and
others coated with silica spheres. These
structures bounce the light around inside
the wrinkle—total internal reflection—
and soften the look of the wrinkle without the use of opaque pigments.
Simple light reflections are another
way to hide wrinkles. Since the wrinkle
is depressed from the skin surface, light-reflective particles at the base of the
wrinkle will make the crevasse reflect
more light. “That will make the wrinkle
be coated with
titanium dioxide and
other substances to
or colors that appear
to change with the
angle of view.
Younger cosmetic wearers may have
more blemishes than wrinkles, and
composite particles can help them too.
Researchers at Avon Products Inc.,
according to their patent application,
embedded sub-micron-sized alkyl silane-treated titanium dioxide particles into
silicone gels. The embedded particles
increase the refractive index of the gel,
which then scatters incoming light away
from the blemish underneath.
Another blemish-hiding makeup formula uses two kinds of 10- to 20-µm-wide
alumina platelets: one treated with metal
oxides and the other covered by titanium-coated spherical silica. “Together, the
two different platelets form the mosaic,
which gently reflects light and matches
the natural color of the skin,” wrote the
team from Color Access Inc. of Melville,
N. Y. (U.S.A.), which patented the idea.
Still other concealers described in patent
applications use tiny glass beads or platelets coated with nylon or even silver.
Iridescence and pearlescence
Glass and mineral cosmetic particles
can be coated with titanium dioxide
and other substances to produce iridescence, or colors that appear to change
with the angle of view. When applied to
the skin, such particles form a semi-transparent layer that creates phase-shifting and interference effects, and
some wavelengths of light are attenuated more than others. Iridescence
happens in nature—in pearls, mollusk
shells, butterfly wings, peacock feathers
and some insect exoskeletons.
Pearlescent pigments are generally
shaped like flakes instead of spheres.
Originally, tiny platelets of mica were
coated with metal oxides with a higher
refractive index than the mica substrate.
Since natural mica tends to be somewhat irregular and can scatter light too
much, cosmetics companies have been
making artificial platelets of materials
such as borosilicate.
Color researchers manipulate the
types of substrates and coatings to
enhance the reflection and interference
of certain wavelengths. At L’Oréal,
scientists have attempted to create
appear less deep, and it will fool the eye
into thinking that the skin surface is
more even than it is,” she said.
“It is very much an optical illusion,”
Draelos said. “You can create some very
interesting optical effects with very small
particles of pigment.”
[ Cross-section of hypothetical makeup particle ]
Diffused inner reflection
Nick Morante Cosmetic Consultants
Cosmetics made of multilayered particles reflect and transmit diffuse light to conceal
wrinkles or impart different colors to observers at different viewing angles. (Inset)
Cosmetic-grade pigment of TiO2-coated mica particles.
46 | OPN Optics & Photonics News