OK, so if I start explaining what a necklace, a bracelet or earrings are, you'll probably immediately close this page because my approach will be too simplistic, bear with me however as I relate some interesting discoveries I have made on my journey with jewellery so far.

Tiaras
Tiaras have long been fashionable, particularly in the last two decades of the 1800s. In fact they were so fashionable that many necklaces of that period were made from rigid metal frames to allow them to be worn as tiaras too. Tiaras these days are probably limited to weddings and royalty and so far I haven't come across many whilst buying jewellery.
In the 1800s and early 1900s the rules for wearing tiaras were very strict. If an occasion required full evening dress then there was a chance or possibly a requirement that tiaras would be worn and in the early 1990s this was often stated on invitations. Strictly speaking, the first time a woman wore a tiara was on her wedding day and thus, at formal occasions, girls and unmarried women were forbidden from wearing them.

Tiaras of gold leaves in archaeological styles were common in the 1860s, by the late 1800s tiaras were often graduated rows of spikes with trefoil motifs or scrolled lyre designs. Winged designs and clustered motifs of flowers or stars were common designs in the early part of the twentieth century and were characteristically exuberant in their style and thus the preserve of the wealthy elite. By the 1920 the tiara had been replaced the bandeau which was well suited to the art deco style and to the new fashion for evening dresses with straight lines. The traditional tiara made a bit of a comeback in the 1930s for formal occasions as the bandeau lost favour but by the 1940 jewellery hair ornaments of any type were no longer fashionable.
Of course tiaras were not the only jewelled hair ornament worn... 

 Combs and Brooches
I have come across more combs in my tour of vintage jewellery as their popularity has remained more constant than that of the tiara, although they have never been amazingly popular. Generally less elaborate than tiaras and so worn on less formal occasions, the myriad of designs makes these a fabulous accessory. In the late 1800s comb designed were often art nouveau inspired and carved in unusual materials such as horn and enamel.  Brooches were also often worn in the hair during this period. The tradition of wear both combs and brooches has always existed but dwindled into the twentieth century, except for special occasions such as weddings. Nevertheless, some beautiful modern and vintage examples exist. 

 Hairclips
Hair clips became increasingly popular towards the end of the twentieth century and have remained a fashionable accessory in novel and jewelled form, for both everyday and occasion wear. During the 1960s the fashion for jewelled hair ornaments of any type almost disappeared, as it did during the 1940s. A brief revival for clips and brooches to adorn the elaborate piled up hairstyles of the 1950s did occur, but no return to the elaborate jewelled pieces of the early 1900s and late 1800s was seen. Clips were very popular in the 1920s, being worn whenever a bandeau was not ..