The typical hairstyle of the 1840s and 1850s was a bun at the back of the head with slight variations. At the beginning of the 1840s the bun was worn low, in the later 1840s it was worn high at the back of the head, and in the 1850s it was again worn low in the neck. The hair was parted in an Y shape, which can be seen in this 1854 painting. The bun could be just a twisted strand of hair; but the hair could also be braided (-> my tutorial) or rope braided before it was put into a bun. For evening wear the bun was more elaborate.
During the day, the hair was usually covered: indoors with a day cap, and outside with a bonnet. The day cap (other names: morning cap or breakfast cap) was worn worn in the early part of the Victorian era by all women (young, unmarried and married women), later just by married women, and since the 1860s or 1870s mainly by older, married women. The front hair was worn in curls or loops.
Early 1840s hairstyles (low bun)
‘The front hair in bands, with or without the ends braided, and turned up again, or in long full ringlets. The back hair is still worn dresses as low as possible at the back of the neck, in braids, chignons, and rouleaux.’ (1840, Godey’s Lady’s Book)
Mid to late 1840s hairstyle (side ringlets, high bun)
The hair is still being worn in full ringlets on each side, the back part tastefully arranged in plaits caught with a handsome comb’ (1843, Godey’s Lady’s Book).
Mid 1840s to mid 1850s hairstyle (loops over the ears)
Here’s a 1845 photograph of a woman wearing hair loops covering her ears. She also wears her bun a bit lower as in this 1849 painting of a similar hairstyle. The bottom of the hair loop in this 1850 painiting is nearly parallel to the floor, while late 1850s side loops of hair are more sloping.