Featured Black Lines in Glass Not cracks Inclusions?

Hi all,
Glass fishing floats - what are these black lines in the glass? Not cracks, some sort of an inclusion in the glass? Something that happens when they are made? The blue balls are definite floats, they have been in the water as there are marks on them that don't show in the photo. Not modern pieces, they are heavy glass. Living on the West Coast I'm familiar with fishing floats so I'm sure these aren't the decorative ones made in the 1970s although I do admit I've never come across a purple one before. It is a thick heavy glass you expect with glass floats. So are the black lines something from when the glass is blown/made?
any information appreciated
thanks for looking

 

Frit trail in the glass probably.

 

Floats aren't the highest quality glass, and I think lines like those are fairly standard.

 

wonderful, thanks bear

thanks MOS could be fairly standard, I've just never noticed lines before

 

My glass floats are my avatar photo. Most of them have "junk" in the glass. They were intended as floats in water so no one even tried to make them look pristine. Maybe some of them are better quality, those that were made as decor in the 70s 80s. Remember when peeps hung nets on the wall with some decorative colored glass balls and called it decor, like near the pool or on the screened in porch? If you're selling them, the photos you posted are perfect to show the imperfections.

 

Yup, they’re industrial glass so the imperfections aren’t seen as an issue.