They
can last for 6-12 weeks, and tend to
fade or lighten over this time. The
red dyes seem to be the quickest to
leak out of the hair, and as a result
the hair can look drab after a few washes.
Semi-permanent dye
preparations do not contain bleaches,
and are therefore safe to use. They
can be used at home. Without bleach,
however, they cannot color hair lighter
than its natural shade.
Lightening hair |
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Color
of nicotine-stained skin. It needs
to be tinted as well as bleached if
it is to be turned white or a 'platinum'
blond.
The stages of lightening hair
The color of hair changes as it is
lightened, as more and more eumelanin
and then phaeomelanin is removed step
by step.
Suppose that a black-haired
client decides she would like to be
a platinum blonde. To make this change
at a single session, her stylist would
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Hair
is made lighter by changing part
or all of the melanin pigment
in the cortex into a colorless
substance. The melanin is not
washed out of the hair - it is
changed chemically, and the change
cannot be reversed.
The chemical
solutions used are called bleaches.
They contain oxidising agents,
like those in neutralising lotions
for perms, in alkaline solution.
The bleach most commonly used
is hydrogen peroxide. Hydrogen
peroxide can be used alone to
lighten dark hair, or together
with a coloring agent (a tint).
As you will
recall, red and blond hair contains
more phaeomelanin than eumelanin.
On the other hand, dark hair -
black or dark brown -contains
more eumelanin than phaeomelanin.
Of the two kinds of melanin in
hair, eumelanin is the more easily
removed from the cortex by bleaches.
This is why bleached dark hair
tends to look reddish: the
eumelanin has been decolorised,
and what is left is mostly phaeomelanin.
Further bleaching removes the
phaeomelanin too. This is also
why red hair is harder to bleach
than dark hair.
Strongly
bleached hair looks yellowish,
because keratin itself is naturally
pale yellow. This natural color
is the reason why an elderly person's
white hair looks slightly yellow
at the roots, as mentioned in
Chapter 1. It also explains why
repeatedly bleached hair looks
the |
The
eumelanin has been removed more
easily than the phaeomelanin from
this
dark hair, hence the partly-colored
appearance |
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