Indentifying White Plate Glass Photo

I have a older peice that is on a white glass plate. The glass seems brittle and almost like a coated piece of paper. The front side of the glass has an eggshell like finish while the back side is glossy. Im at a loss at identifying this and you guys seem very knowledgeable. Any help is appreciated!

Your photo might be an toovytype also known as Ivorytype
Follow the link below for more informations
http://albumen.conservation-us.org/library/c19/toovytype.html

Dominik