Thought this would be interesting in light of the recent discussion of surface milk swirls. This is a CD 731 McKee that has a very unusual surface etching pattern. For some reason the etching has attacked the surface of this insulator in a swirly pattern, almost like wood grain. Some parts of the surface are just fine though... still showing the shinyness of un-etched glass. The etched parts look like typical "sick glass", with some of the iridescent colors that are often seen. They are clearly etched into the surface... you can feel it with your fingernail. I am thinking that this is the result of incomplete chemical mixing in the glass, in some way that left some parts of the surface more susceptible to etching and other parts resistant. Perhaps this explains some of the other examples that look like surface milk swirls?

For a closeup of the surface [id=277488857]