Uncover The Past A Beginners Guide To Identifying Antique Glass Bottles By Their Bottom Markings

For many collectors, the secret to identifying a glass bottle isn’t on the label or the shoulder—it’s on the bottom. The base of a bottle can reveal how it was made, when it was made, and often who made it. For appraisers, dealers, and history-minded enthusiasts, reading those clues correctly transforms a mystery vessel into a well-dated artifact with context and value.

This guide introduces the most useful base features—manufacturing scars, mold seams, maker’s marks, date codes, and other symbols—so you can recognize true antiques, avoid common misreads, and build confidence in your attributions.

Why the Bottom Matters

The underside of a bottle usually survives with fewer alterations than labels or side embossing. Factories placed maker’s marks, capacity codes, mold numbers, and date codes on the base to keep them out of sight. Manufacturing scars—created by the tools and machines that formed the bottle—are also most visible underneath.

Base clues can help you:

• Date the bottle within a broad period or specific decade.
• Identify the manufacturer and sometimes the plant.
• Distinguish hand-blown from machine-made examples.
• Separate original 19th-century glass from 20th-century reproductions.
• Assess relative rarity and desirability.

No single mark tells the whole story. Think of the base as a starting point that you confirm with form, lip finish, seams up the body, glass color, and known product histories.

How Bottles Were Made: Reading Manufacturing Scars

The transition from hand-blown to fully automated bottle-making left distinctive base features. Learn these first; they anchor your dating.

• Pontil scars (generally pre-1860, with some later exceptions)

  • Open pontil: A rough, irregular scar where the pontil rod detached from the base. Often sharp to the touch. Common on early bottles, typically pre-Civil War.
  • Iron pontil: A smoother, circular scar sometimes showing dark/gray residue from iron. Frequent on mid-19th-century soda and mineral water bottles.
  • Sand pontil: A granular, sandpaper-like ring from a sand-coated pontil. Mid-19th century, commonly on utilitarian bottles. Caution: Some 20th-century studio art glass also shows pontil scars; consider overall style and context.

• Hinge-mold seam (roughly 1820s–1860s)

  • A straight seam across the base—like a hinge line—indicates a two-piece mold that opened like a clamshell. Often paired with a hand-applied lip and no machine marks.

• Post-mold circle (c. 1850s–1890s)

  • A circular depression or mark in the center where a “post” closed the base. Typically seen on bottles that still exhibit hand finishing at the lip.

• Cup-bottom mold ring (1860s onward)

  • Instead of a seam across the base, you’ll see a circular ring at the outer edge of the base, where the bottle sat in a “cup” while the body was blown or pressed in a separate mold. This becomes common in later 19th-century production.

• Suction scar (Owens Automatic Bottle Machine, 1903 onward)

  • A circular, often off-center whirl or “suction” scar caused when the machine drew molten glass into the mold. Its presence strongly suggests 20th-century, mass-produced, machine-made glass.

• Valve or ejector marks (20th century)

  • Small circular or rectangular marks from automated mold ejection. Combined with uniform mold seams and a tooled or machine-applied lip, they confirm machine age.

• Push-up or kick-up

  • A domed inward base, especially on wine or champagne bottles. Deep push-ups are common on 18th- and 19th-century “black glass” wines; shallow modern push-ups are for stability and sediment but don’t date the bottle alone.

These scars tell you how the bottle was formed. Pair them with maker’s marks and codes to narrow age and origin.

Decoding Maker’s Marks and Date Codes on the Base

Many North American manufacturers embossed a logo on the base. Below are common marks you’ll encounter and broad date ranges. Always verify with body style and use context, as molds and marks overlap.

• Owens-Illinois Glass Company (O-I)

  • Mark: An “I” superimposed over an “O.” Early versions (1929–1954) often appear within a diamond; later versions (1954 onward) typically omit the diamond.
  • Date/plant codes: Usually formatted as Plant Number (left of logo) – Year Code (right) – Mold Number (below or nearby). Example: 7 [O-I] 45 indicates Plant 7, 1945. Year codes are commonly two-digit after about 1940; earlier codes may be single-digit and repeat each decade—use context to resolve ambiguity.
  • Often paired with a suction scar.

• Illinois Glass Company (pre-merger)

  • Mark: A “Diamond I” (I inside a diamond) and/or IGCo. Common circa 1915–1929.
  • Helps anchor a bottle to the late hand-transition/early machine period.

• Hazel-Atlas Glass Company

  • Mark: H over A (a capital H with a small A beneath or within it). Approx. 1923–1964.
  • Found on tableware, jars, and containers; numbers are usually mold identifiers, not dates.

• Anchor Hocking Glass Corporation

  • Mark: An anchor with an overlaid H. Beginning 1937 onward.
  • Common on household bottles and jars.

• Whitall Tatum Company

  • Mark: WT or WT Co (sometimes with numbers). Mid-19th century into the 1930s; the company sold in 1938.
  • Often on pharmaceutical and apothecary bottles; many are mold numbers rather than dates.

• Brockway Glass Company

  • Mark: B in a circle or “BROCKWAY.” Generally mid-20th century and later.
  • Frequently accompanied by date codes similar to other machine-era marks.

Other marks you may see:

• “Duraglas” (more often on the heel) signaled a proprietary glass finish used by O-I from the 1940s onward.
• “Federal law prohibits sale or reuse of this bottle” appears on liquor bottles, primarily 1933–1964; sometimes paired with base codes that refine the date.
• Country abbreviations (e.g., U.S.A., CANADA) or city names can locate the plant or market.

Dating pitfalls:

• Not every number is a date. Most two-digit numbers on bases are mold numbers or capacity codes.
• Date codes repeat each decade. Combine with label style, closure type, and product history.
• Marks linger on molds. A factory may continue using an older marked mold after a logo change.

Numbers, Symbols, and Other Clues Underfoot

Beyond logos, base embossing includes a mix of functional information. Learn to sort signal from noise.

• Mold numbers

  • One- to three-digit numbers (e.g., 7, 23, 114) typically indicate the specific mold cavity. They help quality control, not dating.

• Capacity and content marks

  • Embossed “6 oz,” “12,” “1/2 Pt,” or metric equivalents indicate capacity. On jars, “PATENTED” lines and graduations can be telling; for instance, early Mason-related patents often appear on the base.

• Symbols and letters

  • Stars, triangles, or single letters often denote mold series or shift marks. Without a known key from the maker, they rarely date the item by themselves.

• Registration and property statements

  • Statements like “PROPERTY OF…” or “REGISTERED” are common on soda and dairy bottles. The phrasing and typography can be period-specific but must be cross-checked with local histories.

• Stippling

  • A field of tiny raised bumps on the base improves strength and scuff resistance—most common on late 20th-century containers. Heavy stippling suggests modern manufacture.

• Color clues (indirect but helpful)

  • Aqua glass dominates 19th-century utilitarian bottles. Clear flint glass becomes standard in the 20th century.
  • Glass decolorized with manganese (common pre–World War I) can turn amethyst after prolonged sunlight. Selenium-decolorized glass (post-1915) may develop a light straw tint with UV exposure.

• Wear patterns

  • Honest base wear (fine circular scuffs) accumulates from long use on hard surfaces. Be cautious: artificial “tumbling” or polishing can reduce wear and obscure original scars.

Remember: base features work best in concert. A suction scar plus an O-I logo and a two-digit year code is strong evidence. A lonely “23” is not a 1923 date unless other features agree.

Condition, Rarity, and Context: Avoid Dating Traps

• Reproductions and commemoratives

  • Some modern reproductions mimic pontil scars or old hues. Machine uniformity, stippled bases, and incorrect mold seams are tell-tales. Compare the lip finish and embossing style to known originals.

• European vs. American practice

  • European makers may use different logos and date formats, and certain forms (e.g., deep-push-up wines) persisted longer overseas. If the base mark is unfamiliar, consider origin before assigning a date.

• Product category norms

  • Pharmacy, soda, dairy, beer, and liquor bottles all adopted machine production at different paces. For example, applied color labels (ACL) on sodas become common from the mid-1930s onward; pair that with base marks for a tighter date.

• Reused molds

  • Molds were expensive and repaired rather than replaced. An older logo can persist for years. Assess whether the lip and side seams match the era implied by the base.

• Value considerations

  • Base marks can confirm sought-after makers or early manufacture, which influences value. But condition (chips, stain, haze), color scarcity, embossing strength, and local desirability often matter more than the base alone.

Practical Field Checklist

Use this quick sequence when you pick up a bottle:

• Clean the base gently to expose marks; avoid abrasives.
• In good light, photograph the base square-on and at a shallow angle to catch low-relief embossing.
• Run a fingertip across the base: feel for pontil roughness, suction swirls, or seams.
• Note the base seam type: hinge line, post circle, cup-bottom ring, or smooth with ejector marks.
• Look for a maker’s logo; sketch or photograph it clearly.
• Record numbers around the logo separately: left (plant), right (year), bottom (mold), if present.
• Check for capacity indicators and any “REGISTERED” or property statements.
• Observe stippling or modern features that suggest later manufacture.
• Cross-check with the lip finish, body seams, color, and product style.
• Log everything: dimensions, color, weight, and context of where it was found.

FAQ

Q: Is a number like “23” on the base the year 1923? A: Usually not. Most two-digit numbers are mold identifiers. Some companies used year codes, but they appear in specific positions relative to a known logo (e.g., to the right of an Owens-Illinois mark). Use the whole layout, not a single number.

Q: How can I tell a real pontil scar from a fake? A: Genuine pontil scars feel irregular and look integrated into the glass, often with small radiating stress lines. Faked scars may look too uniform, lack associated 19th-century features (like hand-tooled lips), or appear over-polished. Always corroborate with form and seams.

Q: Does a suction scar automatically mean the bottle is modern? A: It means machine-made, not necessarily modern. The Owens machine dates from 1903, so a suction scar places the bottle in the 20th century (or later). Pair with logos and codes to narrow the decade.

Q: Are Hazel-Atlas and Anchor Hocking marks easy to confuse? A: Yes. Hazel-Atlas uses an H-over-A monogram; Anchor Hocking uses an anchor with an H. Both occur on mid-century ware. Compare the symbol shape carefully, and use accompanying numbers as supporting evidence, not alone.

Q: Can base markings determine value by themselves? A: They establish age and origin, which are value factors, but condition, rarity, color, embossing strength, and category demand usually drive price. A common bottle with a clear mark may be worth less than an unmarked but scarce variant.

By learning to read bases—starting with manufacturing scars, then decoding logos and codes—you’ll quickly separate eras, recognize makers, and place your bottles within the evolving story of glass production. With practice, the underside becomes a roadmap to provenance and a reliable foundation for appraisals.