Are you sure it's " ivorine " ?
The detail is excellent. identical to the prints / engravings of this.
I wouldn't know what its made from :-( But just from looking at the way it is made would have to think this was done way before the days of lasers and wondering if computers did this kind of thing back then. Someone had to transfer the picture on to the medium and then hand (?) etch all the details in. Nothing is painted on. Every bit of the detail is etched into the tile ,whatever the 1/4" thick tile is made from.
Here is some of the detail work the second of the horses leg and hoof. It almost looks like the picture was burned and melted into it
Here is the back. There was cardboard covering it that was ripped so I removed it. I marked where the tile was nailed into the frame. The back stuff is the old tape that was holding the cardboard on
It really is a nice vintage piece. I like it. You cant get this kind of things at a Michaels, a Hobby Lobby or even a Walmart. its from a time long gone