Looking for an education on glass flaws.

[Dug]

I have a plain food jar that is an iron pontil. At first I thought the heavy lines in the glass was a result of sickness since you occasionally see them on very sick bottles. In this situation I'm thinking that these were formed when the bottle was made somehow. They are deep as if a manmade object etched them as it was spun out. If you notice closely there are a formation of bubbles in the neck that are following the same pattern. Anyone seen something like this before?

 

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[Bass]

I think it sickness. Do the swirls go all around the bottle in spiral design? I'm guessing likely not. I think it's just sickness from being in the ground many years and mineralization wearing away at the glass. Just my opinion. The bubbles matching the same pattern I can't explain. I think that's just coincidence or I could be way off base and wrong altogether. Good photos by the way

 

[Dug]

I think it sickness. Do the swirls go all around the bottle in spiral design? I'm guessing likely not. I think it's just sickness from being in the ground many years and mineralization wearing away at the glass. Just my opinion. The bubbles matching the same pattern I can't explain. I think that's just coincidence or I could be way off base and wrong altogether. Good photos by the way

Just looked closer and it is a single spiral. One complete spiral that runs like a candycane. It has a slight hiccup near the base where it sort of looked like a Z but finished off at the base. The line is pretty deep and you can easily feel it when handling the bottle.

I will try to get a couple close ups of the spiral.

 

[Dug]

Here are some more shots. You can see the Z, almost as if when whatever was etching the bottle struck the seam it went erratic. BTW, the seam near the bottom is very rough and kind of flawed also.

 

[sandchip]

I call those gather lines, resulting from when the blowpipe is inserted into the molten batch, rotated and withdrawn so the helper could cut it loose, resulting in that spiral sort of line that you can follow from top to bottom. Then it's rolled on the marver to make it a bit more uniform, given a puff, rolled again before inserting into the mold and blown. Something about this process seems to affect that which first contacts the marver and that (the lines) which does not, resulting in a slight difference in the hardness of the glass and its resistance to etching, which becomes more apparent upon years of exposure to the chemicals in soil, which is why they are often referred to as "ground lines" which is a bit inaccurate because there are plenty of old bottles which were never in the ground that exhibit these lines.

Also, the roughness on the mold line near the bottom is where the gather was pinched between the mold halves, and chipped away after the bottle cooled and sent on the way to the customer. Unrelated to the gather lines.

Beautiful berry jar, by the way!

 

[Dug]

Hi Sandchip. Thank you berry much, I mean very much for the education. Just what I was looking for.

 

[Bass]

There you go. That's why I asked if it was a spiral

 

[Harry Pristis]

That's a good, thorough explanation by Sandchip! I've thought of these as "stress lines," from stresses frozen into the glass as the gather was manipulated. I like the "gather lines" term, and will adopt it.

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These lines wear differentially from unstressed glass. You can see them in chemically or mechanically-etched bottles. Perhaps the twisting and pinching of the glass that produces this phenomenon make these threads denser or otherwise more durable than less-stressed glass.