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hair and polarized light

dr. TARGET="frame86820">Andrea Marliani

dermatologo - endocrinologo

in Firenze

Microscopy in polarized light, traditionally used in
mineralogy, is now also of indisputable value in trichology.

Keratin, a sequential, repeating crystalline protein, has the
property of retarding the wave of polarized light passing through
it, so that under the microscope a hair appears as luminous and
coloured against a black ground.

Retardations of the wave due to the thickness of the keratin are
defined as “polarization colours” and each colour
corresponds to a precise diameter. Those also resulting from the
crystallographic pattern and from pigments are defined as “compensation

Just as in mineralogy the colours denote membership of a precise
crystalline order, in trichology they permit appraisals of the
hair’s structure, that is, its keratinous “quality“,
thus supplying data for otherwise only hypothetical evaluations.

- Since “compensation colours” can only be assessed
on the basis of their sequence during rotation, the slide must
be studied on a rotating plane and never with a light transmitted
by an optical fibre.

- An ocular micrometer is indispensable for matching the colours
to be seen with the true diameter of the hair under examination.
Knowing the true thickness and seeing the polarization colours
makes it possible at the clinic to match the observed keratinous
fibre under examination.