The 'F.I.' stands for Ferdinand Imperator, who became Emperor in 1835. The plate was worn until 1848, when his nephew Franz Joseph inherited th throne. It was worn on a short horse-hair crested helmet. In 1866, after the disastrous Six Weeks War with Prussia, the cuirassiers were amalgamated into the dragoons.
This plate differs from the 1806 model principally in being shorter (in height) and the metal thinner. This information comes from Stefan Rest of Vienna, an authority on the subject. The ordinary English/American collector would find it hard to spot the difference.
It is of die-struck copper gilt (mercury gilding) two-piece construction, the intials being pinned onto the reverse, and measures 17cm across the base. The V-shaped cut at the top is original to the helmet, as this was where it slid under the forward elements of the gilt-mounted stiff horse-hair crest. The small square holes on each side (one missing) are for the mounting bolts which secured the piece to the body of the helmet.
It is very frail: there is severe crackelure above the initials and several age splits throughout the piece, including a chunk of metal missing at one corner. The gilding throughout is generally quite good, with age corrosion scattered throughout the piece and some severe scratching to the centre and right-hand sections of the plate.
Examples of Napoleonic KuK officers' helmets/plates are now very hard to find.
Prov: from the J.R. Gaunt & Son Ltd. Pattern Book Archive, sold at auction by order of the National Army Museum, London.