How to date antique bottles: seams, pontil scars, lips and base marks

Follow the side mold seam up the neck. If it runs right over the top of the lip, the bottle is machine-made, almost always after about 1905; if it stops or fades below the lip, it was finished by hand, typically before about 1915. Then narrow the date with the base (a pontil scar means about the Civil War era or earlier), the style of lip, and any embossed wording or maker's codes.

By the Antique ID team · Updated 2026-10-13

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The backbone: the BLM and SHA bottle key

The Historic Glass Bottle Identification & Information Website was begun by a Bureau of Land Management employee in 2003-2007 and is now hosted by the Society for Historical Archaeology (SHA). It is written as a key for dating and typing utilitarian bottles and jars made in the United States and Canada between the late 1700s and the 1950s. Its authors stress that bottle dating is not precise: from physical features alone, most bottles can be placed in a range of 10 to 15 years. New techniques spread slowly, old ones lingered, and bottles were often reused for years, as Jane Busch documented in the SHA's journal. The steps below follow the site's key.

Step 1: mouth-blown or machine-made?

Almost every bottle from the later 19th and the 20th century was blown in a mold, so it has vertical side seams. The SHA key asks where they end. If the side seam runs to the very top of the lip and onto the rim (and the rim is not ground flat), and there is a horizontal seam just under the lip, the bottle was made by a semi-automatic or automatic machine. Such bottles virtually always date after about 1900 for wide-mouth jars and after about 1910 for narrow-neck bottles. If the seam stops or fades out below the lip, the bottle is mouth-blown and typically predates 1915; the vast majority of U.S. mouth-blown molded bottles were made between about 1820 and 1915.

The site warns against the old "seam thermometer" idea, popularized in a 1963 collector's book, that the higher the seam the later the bottle. Hand-tooling a lip often erased the seam up to an inch below it, so the exact height of the seam on a mouth-blown bottle is not a date.

Step 2: mouth-blown bottles

Pontil scars

A pontil scar is the rough mark left on the base where a rod held the bottle while the lip was made. The SHA key says utilitarian bottles with pontil scars usually date to the Civil War era or before (about 1860-1865 or earlier) and virtually always before the early 1870s, because between the mid-1840s and mid-1860s the pontil was replaced by snap-case tools that leave no mark. Ninety-five percent or more of mouth-blown utilitarian bottles without a pontil scar date after 1865. Decorative "specialty" bottles, such as barber bottles, can have pontils much later.

Applied versus tooled lips

Base seams and air vents

A straight seam across the base (hinge mold) usually means about 1855 to the early or mid-1870s; a round seam inside the base (post-bottom mold), the mid-1850s to about 1890. Tiny raised dots from air vents drilled in the mold point to about 1885-1890 or later.

Step 3: machine-made bottles

• Owens suction scar. A circular scar with a feathered edge on the base is the mark of the Owens Automatic Bottle Machine. The site notes it was patented and first used in a limited way in 1903, with licenses from late 1904, so such bottles date from 1905 and usually after 1910. By 1917 no more than about 10% of U.S. bottles were still made by hand.
• Valve mark. A round mark on the base of a jar indicates a press-and-blow machine.
• Owens-Illinois codes. The Diamond O-I mark dates from 1930 to the mid-1950s. A digit to its right is usually a year code and a number to its left a plant code. The word Duraglas and a stippled base edge were first used in 1940.

Step 4: embossed wording and color

• FEDERAL LAW FORBIDS SALE OR RE-USE OF THIS BOTTLE was required on all U.S. liquor bottles from January 1, 1935, until repeal in 1964.
• Contents or capacity embossed or labeled (such as "12 oz.") became common only after the 1913 Gould Amendment to the Pure Food and Drug Act required quantity statements.
• Sun-colored amethyst. Glass decolorized with manganese turns pink to purple in sunlight. The site dates most such bottles to about 1890-1920; a pale straw tint instead suggests selenium or arsenic, used from about 1912.

Reproductions and altered bottles

The SHA key quotes a 1969 study by the bottle researcher Julian Toulouse: any technique, once developed, can be used right up to the present, so a hand-finished look alone is not proof of age. Mid-20th-century reproductions and "fantasy" bottles exist, and the site points to research showing that some bottles have been artificially irradiated to turn them a deep, unnatural purple. Check several features together: a genuine early bottle shows consistent evidence in its seams, lip, base and glass.

What drives value

The SHA site deliberately does not discuss value, partly because doing so may encourage illegal collecting. Collectors generally weigh rarity of the embossing and maker, color (unusual colors draw more interest than common aqua or clear), age, crispness of embossing, and condition, including chips, cracks and internal staining. Before digging, make sure you have the right to collect on that land. For researching sold prices, see how to find the value of antiques; for glass that glows under a black light, see uranium glass.

Next steps

Photograph the whole bottle, the lip and the base, then scan it with Antique ID for an identification, a likely date range and an estimated value. An estimate is not an appraisal; for a rare embossed bottle, consult a bottle specialist or auction house.

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