Has Anyone Seen This Method of Sealing Ambrotypes?

[John S. Rochon]

Hi Everyone:

I'm hoping someone can tell me about this method of sealing UK ambrotypes and whether it was a common practice or particular to one area or ambrotypist.

As seen in the photo, the ambrotype is totally encased, front and back, in this faux leather-type material except for the window showing the image.

Any feedback would be much appreciated.

Thanks!