Victorian photography technique

I have found some old photos of OH's grandmother, born 1876.

When I first saw them, I thought they were glass because they are so shiny -but they aren't - they seem to be on a very hard, thick sort of card. The surface is very shiny to touch. I am wondering how they were made, as the quality seems so exceptional. Also they all feel quite heavy. Does anyone have any ideas please?

I have attempted to scan one of them