Can any button experts tell me what this button is made of?

[Squirrel322]

Found a big white button sticking out of the ground at a sidewalk tear-out. I suspect its glass but I don't really know.

 

[smokeythecat]

Glass? Try using a strong hand magnifier to look carefully.

 

[nhbenz]

Looks like gazed pottery/ceramic to me, but I’m far from expert.

 

[tamrock]

In 1918 the U.S. Government made an extensive survey of the international button market, which listed buttons made of vegetable ivory, metal, glass, galalith, silk, linen, cotton-covered crochet, lead, snap fasteners, glass, enamel, rubber, buckhorn, wood, horn, bone, leather, paper, pressed cardboard, mother-of-pearl, celluloid, porcelain, composition, tin, zinc, xylonite, stone, cloth-covered wooden forms, and papier-mâché. Vegetable ivory was said to be the most popular for suits and shirts, and papier-mâché far and away the commonest sort of shoe button.

I'm thinking a soft paste porcelain or at least that's what that pitting leads me to think ?

 

[Red James Cash]

Looks like bone to me.