This distinguished regiment, one of the ancestors of the Royal Greenjackets, was raised in 1800 for service as a rifle unit carrying the famous Baker rifle. This was a fair bit handier than the smooth bore Brown Bess musket carried by the regular infantry, and infinitely more accurate.
The last battle honour on the plate is Lucknow, granted in 1857, which conveniently dates the piece to c 1860, as that is when the next honour was granted for Peking.
The plate was worn in the middle of a black patent leather crossbelt, on which there was also a pouch with a bugle horn. The lion head boss was also on the crossbelt, with a three-strand silver chain connected to a whistle and socket at the other end.
The plate and backing, I suspect, are unmarked high grade silver, as each of the nuts on the reverse have the queen's head duty stamp punched on them. The lion head boss with the Rifle Brigade soubriquet is also, I suspect, of high grade silver, again unmarked. The washers on the boss are replacements.
The condition of the plate itself is excellent, with a little wear to the highlights, as expected on a piece of this age. The edges of the boss are a little crumpled in places, again suggesting high grade silver rather than double-sided Sheffield plate, as it's that much softer than copper.
This was bought together with the Rifle Brigade sabretache badge.