“Boyd’s Genuine Porcelain Lined Cap”
This marking is one of many slight variations in phrasing found embossed in a circular formation on round milkglass liners (“inserts” or “discs”) , part of zinc screw lids used with the “Mason” style canning/ fruit jars.
The glass liners helped prevent food from coming in direct contact with the metal lid, which otherwise caused a metallic “off-taste” to be imparted to preserved food (not to mention the increased possibility of contamination from bacteria).
Lewis R. Boyd was issued a patent for his invention (#88439) on March 30, 1869. 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 sha.org site : Boyd’s Patent of March 30, 1869.
Tremendous numbers of these glass lids were made, by a number of glass companies, many of whom are unidentified. Some of the earlier lids may have been produced by Consolidated Fruit Jar Company, and/or Hero Fruit Jar Company.
Hazel-Atlas Glass Company (after 1902) is known to have produced large quantities of the inserts.
Although most of them are found in an opaque, or semi-translucent white milkglass, some are seen in “off” shades of milky or “foggy” aqua, green or blue. 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.
It is virtually impossible to assign a specific age to any of these lids. Presumably, the first ones date from approximately 1869. The very earliest versions are said to have been made in transparent glass, with milk glass versions introduced approximately 1871. It is assumed the most of the earlier versions of these liners have the name “BOYD’S” or “BOYD” embossed on them. Later versions may or may not have the name included in the lettering.
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. Many of the metal zinc lids marked “BALL” (in cursive) come with an insert marked “Genuine Zinc Cap for Ball Mason Jars” (no mention of Boyd). Presumably, many of those were made by Ball Bros. Glass Manufacturing Company.
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. They are often found separated from the zinc lid they were once a part of.
Many slight variations in the exact lettering are seen. Some of the lids carry mold numbers, such as “2” or “3”. The mold numbers, especially on older caps, are often hand-engraved and rather crude-looking.
Here are just a few of the lettering variations seen:
1) Boyd’s Genuine Porcelain Lined Cap
2) Genuine Boyd Cap / For Mason Jars
3) [Diamond logo] Genuine Zinc Cap [Diamond Logo] For Ball Mason Jars
4) Genuine Porcelain Lined Mason Cap
5) [Hazel-Atlas mark in center] Genuine Boyd’s Cap / For Mason Jar
6) [M inside a diamond mark in center] Boyd’s Genuine Porcelain Lined
7) Maltese Cross with letters H F J Co (placed inside the four “arms”) – used with lids for the Hero Fruit Jar Company jars.
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