How It Works: Science and Technology - Vol. 8

By Wendy Horobin | Go to book overview

Hair Treatment

The idea of putting waves and curls into straight hair dates back to ancient Egyptian and Roman times. Cleopatra is said to have set her hair in rollers made of baked mud. Early methods, which involved wetting the hair, winding it onto rollers and then drying it, achieved only a temporary set. It is the ability of hair to stretch when it is wet by as much as 20 to 50 percent of its original dry length that makes temporary setting possible.

Permanent waving was invented by Charles Nessler in 1905. Nessler's method involved winding the hair onto rods or rollers, applying an alkaline chemical (usually borax) to soften it, and then heating to fix the hair in its new shape. In the early days, permanent waving was a long, hazardous process because the action of the alkali was difficult to control; if it was too vigorous or was allowed to continue for too long, damage to the hair would result. Nevertheless, Nessler's invention was an important advance on previous processes; for the first time, the chemical structure, rather than just the physical shape, of the hair was altered during waving.


Hair structure

Hair is composed of three layers—a thin, outer layer of semitransparent, overlapping scales called the cuticle, an inner layer (the cortex) composed of thin threadlike fibers of the protein keratin, and a central marrow (the medulla). It is the cortex that is important in hair waving and straightening processes. The fibers of the cortex are held together by chemical linkages called disulfide linkages.


Permanent waving

The principle of permanent waving is to break these links so that the individual fibers in the cortex can move relative to each other as the hair is put into its new shape and then to reform the linkages to fix the fibers in their new positions. In modern permanent waving, the breaking and reforming of the disulfide linkages is achieved chemically and is usually carried out at room temperature, hence the term cold waving is sometimes applied to this process. A reducing agent, usually ammonium thioglycolate, is used to break the disulfide linkages while an oxidizing agent is used to reform them. Acid-balanced perms are better for delicate hair, a gentle curl, or just to add body. They require external heat and usually contain glyceryl monothioglycolate. Hydrogen peroxide used to be the most common oxidizing agent, but other more stable oxidizing agents are preferred. Thus, permanent waving comprises three steps: applying a softening solution (containing the reducing agent), shaping the hair, and applying a neutralizing solution (containing the oxidizing agent) to fix the curl. The number of rollers used and their size depend on the result required and the type of hair—coarse or fine.

The softening and neutralizing solutions often contain additional chemicals, such as wetting or swelling agents, that improve penetration into the hair fibers. To avoid damaging the hair, the softening and neutralizing solutions are normally neither acid nor alkaline, although the action of the softening solution is sometimes enhanced by adding ammonia, which makes it slightly alkaline.

Colorants can be applied
all over the head or
restricted to selected parts
of the hairstyle, such as
when highlights are added
to give a more natural
sun-lightened effect.
Developments in colorants
have made a wide range of
colors available that will
remain in the hair for just
one wash or last several
months.


Straightening

Hair straightening is simply the reverse of permanent waving. As far as is known, it was first introduced in the United States to straighten the tightly curled hair of African Americans. The first hair straighteners were based on caustic soda, a vigorous alkali, but these were generally unsatis-

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How It Works: Science and Technology - Vol. 8
Table of contents

Table of contents

  • Title Page *
  • Contents *
  • Gold 1013
  • Governor 1017
  • Grass-Cutting Equipment 1018
  • Gravity 1020
  • Gun 1023
  • Gyrocompass 1028
  • Gyroscope 1030
  • Hair Treatment 1032
  • Halogen 1034
  • Hang Glider 1037
  • Head-Up Display 1039
  • Hearing 1041
  • Heart 1045
  • Heart Pacemaker 1048
  • Heart Surgery 1049
  • Heat Engine 1053
  • Heat Exchanger 1054
  • Heating and Ventilation Systems 1056
  • Heat Pump 1063
  • Helicopter 1065
  • Hi-Fi Systems 1071
  • High-Speed Photography 1077
  • Holography 1080
  • Hormone 1084
  • Horticulture 1088
  • Hosiery and Knitwear Manufacture 1090
  • Hurricane and Tornado 1094
  • Hydraulics 1100
  • Hydrocarbon 1105
  • Hydrodynamics 1109
  • Hydroelectric Power 1112
  • Hydrofoil 1116
  • Hydrogen 1118
  • Hydroponics 1120
  • Hygrometer 1123
  • Ignition System, Automobile 1124
  • Image Intensifier 1128
  • Immunology 1132
  • Induction 1138
  • Inertia 1142
  • Information Technology 1147
  • Ink 1151
  • Index i
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