I often encounter the question of which hairdos would be suitable for the 18th century, whether a wig was necessary, what to use for poweder etc. Some of the questions, at least for ladies, are answered here, but the source for that isn't contemporary and therefore should be treated with care. A good example for that fact is the so-called "Pompadour hairdo" which hasn't been seen on Madame Pompadour herself.
No other aspect of fashion has suffered under so many half-truths and exaggerations as the rococo hairdo. Even in seemingly serious books you find stories about Fontanges that were four times as high as the head (e.g. v. Sydow, 1880), ladies sleeping in a sitting position so as to preserve the hairdo, or towering structures in which mice nested because the hair (again, to preserve the hairdo) had neither been combed nor washed for some time. There is probably some spark of truth in all those stories, but they shouldn't be taken at face value.
I suspect that the usual secondary sources liked to spread such stories because the authors thought that the subject of fashion history was too dull without some colourful anecdotes to entertain the reader, and "forget" to mention that they're just that: entertaining anecdotes. There was one case that was considered unusual enough to write down even at the time when it happened, which is how later generations learned about them. Nobody wrote down the normal, everyday stuff. As always, the story grew in the telling, was shortened and played up from author to author until the anecdote appeared as authentic fact, even as typical of the era.
For instance, Fontanges really were quite high around 1700, but four times as high as the head would mean a height of one metre - an exaggeration only found in depictions of satirical theatre plays. All it takes is someone who is opposed to the Fontange fashion ("The hairdos are as high as a house!" as in "Potholes a mile deep!"). If you consider how shy mice are, they could only nest in the hairdo of someone who slept very soundly for nights and days on end. It's more probable that between 1770 and 1790 a lady left her wig (with all the yummy pomad and flour powder still in it) in a corner of her dressing room for some weeks - and became the talk of the court for days. As for sleeping upright - what do we really know about that? Paintings of some queen sitting in bed? Maybe they were painted that way simply because it looked better. A physician of my acquaintance has suggested that it had to do with frequent lung problems (due to the draughty buildings): If you've ever gone to bed with a cold, you may have noticed that you cough more when lying down.
In contrast to the distorted picture painted by many secondary sources, women's hairdos were relatively harmelss for most of the century. At the very beginning, until c. 1710, Fontanges (see left) were worn with the front hair piled up high, but the height gradually declined until low, simple hairdos took their place around 1720. Even short curls (à la mouton, i.e. sheep-style) were worn. Most pictures of Madame Pompadour (including the famous green portrait) show her with a simple braid originating at the neck and going up the back of the head and locks around the forehead, similar to the picture on the right (click to enlarge). So, none of the high hairdos generally attributed to the rococo there.
Only after 1770 (Mme Pompadour had died in 1764), hairdos started to rise higher and higher, necessitating the use of wire constructions and hair-pieces. Up until then, women did not have to wear wigs because social convention demanded long hair in women anyway, so pre-1770s hairdos could be realised with the natural hair. I guess that whoever could afford it had a coiffeur do their hair on a weekly or even daily basis, while others had their wig done once a month and wore it maybe once a week.
The ship under sails that we often encounter in books did really exist, apparently: Even contemporary sources support the story, e.g. the copperplate to the left*. The hairdo was created to celebrate the victory of the ship "La belle poule" in some battle. One could imagine that the hairdo was fashionable for a few weeks or - far from the court, to where letters travelled a few weeks - months until it had lost the appeal of novelty. If there is any truth to what we're told about the court of Louis XVI, its members vied for attention, trying to outdo each other at inventing witty remarks, novelty fashions and the like. In such a competition, even the most unusual hairdo would soon have lost its appeal. The same would have happened to all the other extravagant hairdos of the pre-revolutionary decade that were recorded for posterity: Applauded for their ingenuity, imitated by some courtiers, soon dropped out of sight like a joke told once too often.
Powder appears to have been used sparingly by ladies at first, but with increasing frequency after 1750. No suprise if you consider that hairdos mostly consisted of natural hair, the length, fineness and shininess of which they wanted to show off. When hair-pieces entered the picture, powder was a good way of covering up the differences in colour. Those that preserved a hairdo for some time (there may have been people who did) would have profited from the oil-absorbing qualities of powder.
It's true that men usually wore wigs. The main reason is probably that most tend to lose hair from a certain age on, preventing them from wearing the fashionable hairdos. The extremes of men's hairdos roughly coincide with those of women's: Around 1710, the long-flowing allonge wigs went out of fashion along with women's Fontanges. After that, hairdos stay close to the scalp. Except for a few locks around the forehead, the main part of the hair (natural or artificial) is brushed to the back to vanish into a black taffeta bag, the bourse. Later on, some people wore a pigtail wrapped in black fabric, modeled on the hairstyle of Prussian soldiers.
As with the ladies, wigs were more likely to be powdered than the natural hair, altough some wigs were not powdered at all. If you consider that the powder was made to stick to the hair with the help of oily pomads, it is only logical that the long hair did not just hang down in back but was stuffed into a bag or wrapped with a fabric ribbon: Anyone who has seen what skin/hair oil can do to the inside of a shirt collar would not want the same to happen to the outside of a (non-washable) silk suit. The fashion museum in Ludwigsburg exhibits a Justaucorps where the neck/upper back part is discoloured and disintegrated by pomad and powder.
The hairdo that is nowadays considered typical, i.e. with two to four rolls above the ear, is restricted to the post-1760s era and can be combined witha bourse as well as with a pigtail. Only after 1770 and only for a short time, men's hairdos develop an upward tendency, but not quite as extreme as ladies' hairdos of the same period.
Not much is known about 18th century hair care. My main source on cosmetics (Trommsdorff, 1805) doesn't mention a single recipe for shampoo or the like, altough it is quite comprehensive in any other respect. I deduce that normal soap was used, as was the case even in the early 20th century, and then the slight natural acidity of 5,7 pH was restored using one of the many recipes for aromatic vinegars Trommsdorff lists. If you use soap (=basic) on hair without applying some acid afterwards, it becomes sticky-dry. We can safely assume that hair was washed less frequently than it is nowadays, and even then often just with water, without soap. That way, the natural oil would be preserved, making the hair soft and shiny. Some re-enactors tried washing with water only on themselves and found that after a few weeks of adjustment, the hair became very soft and shiny and not in the least oily - and stayed that way even after a year or two of not encountering any shampoo or soap. The "aroma" - if it was perceived at all in an era that was averse to hygiene - was covered up with perfume.
Even around 1880 (v. Sydow), pomads seem to have been popular for making the hair shiny, but according to that book, it was only necessary if you frenquently washed your hair with soap. According to Trommsdorff, some of his pomad recipes are suitable for both skin and hair, so I forgo mentioning any recipes here, but point you towards my cosmetics pages. The basic recipe mentioned there can easily be varied using different scents.
Contrary to the common cliché, neither natural hair nor wigs were necessarily powdered. Most importantly, wigs were not made of white hair as it is often seen nowadays: A good wig was made of real, human hair, but how many white-haired (not yellowish or grey) grannies with long hair were prepared to sell theirs? It was more probable that youngish women had to sell their long hair for financial reasons, i.e. it came in all colours, so the good wigs must have been made of natural-coloured hair. Only low-quality wigs were made of animal hair (buffalo or horse) which would have been available in white, but who would have it made so obvious that they couldn't afford human-hair wigs? Even though white, grey and blond were the fashionable colours (judging from the colours that Trommsdorff gives powder recipes for), an unpodwered wig in a natural hair colour on a re-enactor's head stands out from the usual white buffalo or nylon crowd in a positive way, so I would recommend renouncing powder altogether if it hadn't been so popular.
According to Trommsdorff, hair powder consists of starch (i.e. potato or rice flour), colouring pigments if applicable, and fragrant oils. Zedler's Lexicon (1741) criticises the waste of wheat flour for that very use.
As has been mentioned before, the powder will only stick if the hair is oily, either due to some pomad being applied or due to natural oliliness. With the authentic methods available to us (who has a powder room?), it's difficult to apply the powder evenly, but the authentic look is worth some effort. Since most of us use a wig only two to four times a year, it doesn't make sense to oil it up and powder it only to have it sit in a corner for most of the time, with a good chance of re-enacting the above mice anecdote. A good substitute for powder is called for, and actually there is one: Hair colouring spray that is available in a number of colours, including white and grey. If it's properly applied, it mimicks hair powder quite well.
*) All copper plates on this page are taken from the Krünitz Encyclopedia;
the colour photograph was taken at the museum of the Fürstenberg porcelain