Porcelain dating marks


Tremendous numbers of these glass lids were made, by a number of glass companies, many of whom are unidentified.

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The actual title of the patent is termed “Improved Mode of Preventing Corrosion In Metallic Caps”.

The patent can be viewed here, a pdf file from the site : Boyd’s Patent of March 30, 1869.

They were continued to be made in huge quantities for many decades thereafter, with production probably extending well into the 1950s or later.

The timeline of markings (which ones came first) is uncertain. The lids are frequently found by bottle diggers at old dump sites, or in privies (where outhouses used to stand) along with other durable (non-degradable) items such as bottles, jars, broken dishes, pottery, shards of glass tableware, etc.

Only a very few of them were actually made of true porcelain, the great majority being made of glass, notwithstanding the phrase which would indicate otherwise.