An unidentified member of the Royal Artillery presented in the so-called gemtype format is something of a rarity.
Commonly called tintypes in the United States this specific process was generally known as a ferrotype in Great
Britian. This specific format was know as a gemtype because of its extrememly small size - usually no larger than
1inch x 1 inch. Gemtypes were usually produced in batches and sold mounted in a paper Carte de Visite-sized mount.

Very wide spread in the United States the tintype or ferrotype never gained the same popularity in the United
Kingdom with this small format being even more uncommon.

Carte de Visite-Sized "Gemtype" (Ferrotype)
Walton's Gem Photographs - Photographer
New Biggate, Leeds, England
c. 1865