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Machine made glassware — Safety Rim: any input?

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David E:
Can anyone enlighten me on the tiny bump found on the rim of Dema machine-made glassware?

Following communication with Christine, she tells me this was called a 'Safety Rim' to reduce the likelihood of chipping. I have found mention here under the name 'SIRA':

http://www.rkl-glas.de/_products/catering.php

Other companies also mention 'safety rims', but is this bump a consequence of machine-made glass, or an intentional inclusion for this purpose?

I also found mention that safety rims do not feature before 1970 - can anyone confirm this?

Pinkspoons:
On glass-forums.com Connie mentioned that the safety rim was patented by Libbeys pre-1930.

I have a Holmegaard cannister, mould-blown, dating from 1930 which also features one - so it's not just machine-made glass.

David E:
Thanks Nic: that rules out the date then. Just need to know whether the 'bump' is a side-effect, or deliberate. I think Stephen might be able to help here.

Connie:
What bump are you talking about?  Most safety rim glasses will have a small bump where the glass roll meets.  I think it is a artifact of manufacture.

Pinkspoons:
As far as I know, the bump is what makes the safety rim safe.  ;D

A thicker, rounded rim atop an otherwise thin and fragile piece of glass adds stability to the form, as opposed to just polishing it. The thickness adds strength and the rounded nature of it deflects impacts to some extent. But this is just my own speculation.

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