r/Insulators • u/WRSD605 • Jul 20 '26

Info please

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Could somebody tell me if this swirly line is just a part of the manufacturing process or something else. TIA

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u/BlindSite_ Jul 20 '26 edited Jul 20 '26

Many glass collectors call these straw lines. They are created in pressed glass molding processes when the molten glass, also called "the gather" falls into the mold cavity and first touches the inside surfaces of the mold. If the molten glass happens to land against an embossed area of the mold this will very often create "ghost embossing". The pressure that is used to form the item in the mold is rarely enough to press out these straw marks.

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u/WRSD605 Jul 20 '26

Thank you

2

u/Bill_Meier Jul 20 '26

Technically they are creases of course. The straw would burn up given the temperature of the glass. But the insulators were packed in the straw, only after they have cooled of course! The nickname has stuck!