Medicine or cure bottle?

[Chaser43]

This small bottle stands 4 inches high and shows irridesent rainbow color on the surface.
No embossing is found to tell what it was used as. I assume it was for medicine of some kind. Here are three pics of it.

 

[Chaser43]

The color I speak of does not show in the pics.
Perhaps the pontil bottom could shed light on its relative age?

 

[Chaser43]

Ground, as in rough appearance?
Its smooth I would say.

 

[woody]

It looks to be an early screwtop, as you can see the threads only have a few turns to put the cap on.
Probably 1920-1930's.