The Talking Machine Forum — For All Antique Phonographs & Recordings

If the played part is the brighter black one, playing seems to clean the grooves... As someone said, the greyed part seems to have some kind of dirt giving it that appearance...

The first comment about the sticky surface suggests these may have been stored in a hot place for a few years ( an attic for example ) and the small amount of oleic acid in the wax has sweated out on to the surface due to heat.
The oleic acid is soft and gummy ( think olive oil) and it will probably polish off with the stylus by playing but may gum it up a bit so the stylus will need cleaning a few times I expect .

That could be the clue, and that's why the played part has such good appearance. May be....