Hairstyling tools used to change the structure of the hair with the help of heat. There are three general kinds: curling irons, used to make the hair curly, straightening irons, used to straighten the hair, and crimping irons, used to create crimps of the desired size in the hair.
My aunt Toot-loop used a pressing comb, followed by a curling Iron that she as a pulling technique... She could straighten your hair just like you had a perm. She even made her own hair grease. one for pressing and another just for your scalp .

History:
In 1882, Erica Feldman used heated rods to straighten or style hair, and Marcel Grateau is credited with creating the curling iron years later, in 1890.

Ian Gut gold used hard chemicals on the hair and scalp to straighten hair, but this often caused burnt scalps and hair. Women in the 1960s also used clothing irons to straighten waves and curls out of their hair before the straightening iron tool was created.

Patented a hair straightener in 1906 that comprised metallic teeth that are combed through the hair,  while in 1909 Isaac K. Shero patented a hair straightener composed of two flat irons that are heated and pressed together. However the hair straighteners, as we know them today, are credited to Scottish heiress, Lady Jennifer Bell Schofield, who refined and combined previous efforts into a hinged, two plated heated iron in 1912.

Years later, Sharrell invented heated metal hair-care implements, such as hot combs. The hot metal straightener slid easily through the hair, causing less damage and dryness than previously-used techniques.

 Later, ceramic and electrical straighteners were introduced, allowing for adjustment of heat settings and straightener size.

Hair straighteners must be used on dry hair; straightening wet hair will fry your hair.

An electric curling iron.
Curling irons, also known as curling tongs, create waves or curls in the hair. There are many different types of modern curling irons, which can vary by diameter, material, and shape of barrel and the type of handle. The barrel's diameter can be anywhere from 0.5 inches (1.3 cm) to 2 inches (5.1 cm). Smaller barrels are typically used to create spiral curls, and the largest barrels are used to give shape and volume to a hairstyle.

Curling Irons are typically made either Teflon, ceramic, tourmaline, metal, or titanium, each of which has its pros and cons. The barrel's shape can either be a cylinder, cone, or reverse cone, and the iron can have brush attachments or double and triple barrels.

The curling iron can also have either a spring-loaded, Marcel, or clip less handle. Spring loaded handles are the most popular and use a spring to work the barrel's clamp. They are less expensive and more user-friendly than other models, but they are fragile and can cause a crimp where the clamp is placed. When using a Marcel handle, named after Marcel Grateau, one applies his or her own pressure to the clamp. For this reason, they are more difficult to use, and they are usually used only by professional stylists in salons. Clipless wands have no clamp, and the user simply wraps hair around a rod. Most clip less curling irons come with a Kevlar glove to avoid burns.

Modern Flat-Iron sometimes use ceramic plates.
Straightening irons, straightness, or flat irons, not to be confused with clothing irons, work by breaking down the hair's hydrogen bonds found in the hair's cortex, which cause hair to bend and become curly. Once the bonds are broken, hair is prevented from holding its original, natural form, though the hydrogen bonds can re-form if exposed to moisture.

High-end modern hair straighteners have ceramic heating elements and are more effective due to their constant heat, with a very fast heat-up time (less than 10 seconds). A higher quality plate is the most desirable asset of any flat iron. Better plates straighten the hair more easily and cause much less damage. Very hard ceramic coatings that are sprayed in layers and baked on tend to perform best. Less expensive units usually do not have ceramic heating elements and some may have a paint-like coating that gives the appearance of ceramic plating. These cheaper coatings wear off very quickly and cause more damage to the hair.

A woman's hair before and after using a flat iron There are two types of damage all flat irons create: heat damage and mechanical damage. Heat damage is unavoidable, since the hotter a flat iron, the better it works (up to 450 °F (232 °C)). Less mechanical damage is achieved through smoother plates. Most plates are aluminum and coated with something, such as a hard ceramic coating. As cheaper coatings wear off, the levels of mechanical damage increases.

Daily or very frequent use of a flat iron will damage the hair. Less frequent straightening - every other day, for example - will reduce this damage.

Many Hair-Straighteners claim to use ionic and infra red technology, which claims to seal in moisture and oils and to reduce static and frizz.

Depending on the hair type, repeated use of hair Straighteners, like most other heat styling tools, can cause varying amounts of damage such as split ends, thinning of the hair shaft and even causing hair to become brittle and prone to breakage.

Generally, after extensive damage, hair will show signs of dryness and display an unhealthy appearance. Women and men with extremely curly, thick hair can take 30 minutes to an hour to get the desired look of straight hair, depending on the kind of Straightener that is used.

Women with slightly wavy or already naturally straight hair spend less time and heat straightening it. However, many companies have begun to manufacture heat protection sprays, shampoos and creams which aim to reduce the amount of damage caused by the use of Straighteners.

Hair Straighteners
should only be used on dry hair, unless they are specially made with vents to let the moisture out. These sorts of irons are usually called "Wet Dry" irons. Based on the materials used in the heating plates, hair irons can be classified as ceramic and traditional metal flat irons.
Ceramic hair irons are believed to be more gentle on the hair.

Main article: Hair crimping
Crimping irons or crimpers work by crimping hair in saw tooth fashion. The look is similar to the crimps left after taking out small braids. In 1972, the modern crimping iron was invented by Geri Cusenza, one of the co-founders of Sebastian Professional. Crimping first became very popular in the United States during the mid-1980s.