What I have been told about these tiles, prior to my purchasing them, is that they are hand engraved and inked vintage Ox Bone on Bamboo.  A few of the tiles are plain with no engravings while other have small prints pasted on the back.  By clicking on the second image you can see what is on the backs of the painted Mahjong Tiles. These sets were typically made and brought from China to the US after the mid 1920's. 

For each, I sanded and applied 3 coats of gesso to the bamboo side of the tile. After the painting cured, it was then varnished.