I scored this neat little iodine pencil on etsy not long ago. The design is fabulous, the glass iodine tincture container screws into another protective container, which I believe is a thicker glass although I am not sure. A little searching indicates that this item may be pre-1939 although I cannot be sure as I have no images with which to compare:

science museum group

Boots Iodine Pencil, protective container

Boots Iodine Pencil

Boots Iodine Pencil

Boots Iodine Pencil

Hmmm, I'm not seeing a skull and crossbones on the label!

This photo demonstrates the proper use of an iodine pencil. This is from a 1932 edition of Popular Science, so I'm sure that this was a relatively new item at this time.

Handy Pencil holds Iodine, Popular Science,  1932