Short answers, pulled from the story.
Jean Fouquet painted the earliest known portrait miniature, a self-portrait dated 1450. This work emerged as a radical departure from the religious scenes that dominated illuminated manuscripts and marked the beginning of a tradition that would eventually replace the heavy, book-bound illustrations of the Middle Ages with portable, personal art.
A terrible destruction of portrait miniatures occurred in a fire at White's Chocolate and Coffee House on the 28th of April 1733. Sir Andrew Fountaine had rented two rooms at the location to temporarily hold his huge collection of portraits done by Hilliard, the Olivers, Samuel Cooper, and others, and the entire house burned down.
The use of watercolour on ivory became the standard for portrait miniatures around 1700, during the latter part of the reign of William III. This shift in medium allowed for a new level of detail and luminosity that had not been possible before and quickly became the standard for portrait miniatures.
Jean Petitot was the greatest worker in enamel portrait miniatures between 1607 and 1691. He painted his finest portraits in Paris for Louis XIV of France, and his son succeeded him in the same profession.
The decline of portrait miniatures began in the mid-19th century with the development of daguerreotypes and photography. The daguerreotype, invented in 1839, was the first publicly available photographic process and quickly became the preferred method for capturing portraits.