Information request: Early Rosetta Stone images

[David McGreevy]

Reposting this from a few years ago, I have an 1870s albumen photo by Mansell, and my colleague Thomas Harris has an 1846 Daguerreotype by Mayall of the same image, clearly an early rubbing of the Rosetta Stone with applied graphics. After years of searching we have yet to find any information about it. My albumen has pencil notations on the reverse that suggest someone was trying to decipher a particular hieroglyphic line.

Can someone here suggest a person I can contact at the British Museum about this?  

Many Thanks, David