Imperial Glass Marks: Identifying IG, LIG, and Unmarked Pieces

By the Velqo Editorial Team · Published 24 August 2026

Most guides to Imperial glass marks are organized as a list of logos with dates beside them, which quietly assumes you have a mark to look up. In practice, the majority of people turning a piece of Imperial over find nothing at all, and the ones who do find letters usually reach the wrong conclusion about what those letters mean. The instinct that a mark signals age is exactly backwards for this company, and getting that straight is the difference between correctly reading a piece and confidently misdating it.

Imperial glass marks are letter monograms the company applied mainly in its later decades: the superimposed I over G through the mid-century decades, LIG from 1973 under Lenox ownership, and ALIG from 1981 in the company’s final phase. Most original Imperial carnival glass carries no mark, so an absent mark is normal rather than disqualifying.

Quick identification checklist

Check the base first, in good light and with a close look. Imperial’s letter marks are molded into the glass rather than printed, so they read best when you tilt the base against a window and let the light rake across it.
Decide which family the mark belongs to. The main families are the word marks (NUART, NUCUT), the Iron Cross, the superimposed I over G, and the Lenox and Lorch era letters (LIG, ALIG).
Treat letters as a late signal. IG, LIG, and ALIG point to mid-century and later production. They are not evidence of an early piece.
Treat no mark as an ordinary result. A large share of Imperial’s original carnival production went out untrademarked. An unmarked base sends you to pattern and form, not to a dead end.
Identify the pattern next. Candlewick and Cape Cod are the two most commonly encountered lines and both ran for decades, so a pattern name gives you a wide window rather than a year.
Check whether the mark is plausible for the piece. A late letter mark on a shape and finish that reads as early production is a contradiction worth investigating rather than explaining away.

The company timeline that produces the marks

Imperial Glass was founded in 1901 in Bellaire, Ohio by Edward Muhleman, with production beginning in 1904, and the firm operated until it ceased operations in 1984. That eighty-year span covers pressed tableware, imitation cut glass, an enormous carnival glass output, mid-century revivals, and a final decade of ownership changes.

The ownership chain matters more than it might sound, because it is what makes two of the letter marks so useful. Lenox Inc. acquired Imperial in 1973. Arthur Lorch bought the company in 1981, and the firm changed hands again before operations ended and the assets were dispersed in the mid-1980s. Those transitions are the reason LIG and ALIG are narrow date brackets: each belongs to a late, short-lived phase rather than a stylistic era, so when you find one you have genuinely narrowed the piece to a small part of the company’s run.

The mark families and what each one tells you

NUART appears on lighting and art glass lines from about 1912. Published end dates vary, so treat it as an early mark rather than one that pins a year, but its window is early enough that finding it is meaningful.

NUCUT marks the imitation-cut-glass line and runs from about 1911 into the 1930s, with sources differing on exactly when it was retired. If you are holding pressed glass with a deep, cut-look pattern and a NUCUT mark, you are looking at a piece that was made to imitate expensive cut crystal at a fraction of the cost, which is exactly what it says about the market it was sold into.

The Iron Cross is a cross-shaped mark associated with a small number of carnival patterns. Published sources disagree about when it first appeared, so the honest framing is that it comes into use around the mid-1910s. Treat any single year you see quoted for it as one source’s opinion rather than settled fact.

The superimposed I over G is the mark most people mean when they say “the Imperial mark.” It was in use from the 1950s through the 1970s. It is common, it is legitimate, and it means mid-century or later.

LIG dates to the Lenox period beginning in 1973. ALIG belongs to the short ownership change that followed, starting in 1981 and running to the company’s final years. Both are late, both are narrow, and both are frequently misread by sellers as old marks simply because they are unfamiliar.

Why an absent mark is the normal case

Here is the part the list-of-marks pages skip. Most original Imperial carnival glass was never trademarked. The letter marks are associated with modern and revival carnival production rather than with the original run. That inverts the beginner’s reasoning in a way that has real consequences: a marked piece of Imperial carnival is more likely to be a later revival piece than an early one, and an unmarked piece is not suspicious at all.

That moves the work to the next stage rather than ending it. From a blank base, you identify the piece by pattern, by form, by color and iridescence, and by comparing against documented Imperial shapes. Pattern books and collector catalogs for Imperial are extensive, and shape plus pattern is the standard route to an attribution when there is nothing molded into the foot.

The decision path from base to attribution

Work it in this order, because each step narrows what the next step has to consider.

Is there a mark? If yes, identify which family it belongs to and read off the corresponding window: word mark, Iron Cross, I over G, LIG, or ALIG.
If there is no mark, go to pattern. Name the pattern from the molded design. Candlewick, produced from about 1936 into the 1980s, and Cape Cod, introduced in the 1930s and also produced into the 1980s, are both commonly encountered.
Then go to form. The specific shape (bowl, compote, vase, plate, stemware) narrows a pattern to a catalog entry, and catalog entries carry their own production notes.
Then check color and surface. Iridescent treatments and body colors were not offered continuously across a pattern’s life, so they trim the window further.
Only then reach for a date. A pattern name alone gives a decades-wide range. Pattern plus form plus color is where a usable estimate comes from.

Cross-checking a mark against the piece

A mark on its own never carries an attribution. It has to be plausible for the object it sits on. The mark, the mold quality, the form, and the finish all have to agree, and when they do not, the disagreement is the finding.

Two specific checks are worth making. First, does the mark’s window overlap the pattern’s production life? A letter mark from the Lenox period on a pattern that had been out of production for decades is a contradiction. Second, do the glass and the workmanship match the era the mark claims? Later revival production and pieces made from reissued molds can look convincingly like earlier work at a glance, and mold reuse is common in American pressed glass generally.

Marks from other makers add a further layer. Several glass companies used letter monograms, and an unfamiliar initial-based mark is at least as likely to belong to another factory as to Imperial. Compare the exact letterform rather than the general impression.

Watch-outs and common mistakes

Reading a mark as proof of age. With Imperial specifically, letters usually mean later. This is the single most common error on this topic.
Quoting the Iron Cross start as a firm year. Sources conflict. Say mid-1910s and move on.
Reading a long-running pattern as a date. Candlewick and Cape Cod each span roughly half a century of production. The pattern name is a starting point, not an answer.
Confusing an initial monogram from another maker with the I over G. Look at the actual letterforms and how they interlock, not just the fact that letters are present.
Assuming an old mark means high value. Condition, pattern desirability, color, and form drive interest far more than the presence of any particular mark, and identical patterns can sit at very different levels depending on how sought the color is.

Photo tips

Shoot the base straight on, filling the frame. Molded marks are shallow and low contrast, so a distant shot loses them entirely.
Light the base from the side. Raking light from a window or a lamp placed low makes a molded mark cast a small shadow, which is what makes it legible in a photo.
Set the piece on a plain dark surface. Clear and iridescent glass photographs badly against clutter, and a dark backdrop makes the mark’s edges read.
Take a second photo of the full profile. Form is half the identification when there is no mark, so a side-on shot of the whole piece against a plain background is as valuable as the base shot.
Photograph the pattern detail separately. A close shot of the molded design, lit from the side, is what makes a pattern match possible.

Common questions

What does the IG mark on glass mean?

The superimposed I over G is Imperial Glass Company’s monogram, used from the 1950s through the 1970s. It confirms the maker but points to mid-century or later production rather than early work. If you are hoping the mark dates a carnival glass piece to the early twentieth century, it does the opposite: original Imperial carnival was largely unmarked.

Is unmarked Imperial carnival glass worth anything?

Being unmarked neither helps nor hurts, because most original Imperial carnival was never trademarked in the first place. Value tracks pattern, color, form, and condition. Scarce colors and desirable shapes in undamaged condition consistently draw more interest than common ones, regardless of whether anything is molded into the base.

How do I tell LIG from ALIG?

Both are late Imperial marks built around the same letter cluster, and the difference is the leading A. LIG corresponds to the Lenox ownership period beginning in 1973, and ALIG to the ownership change that began in 1981. Photograph the base in raking light and read the letters carefully, since a shallow molded A is easy to miss.

When to use the Antique Identifier app

Photograph the base in raking light, then the full profile, then a close shot of the pattern. The app reads the mark if there is one and works from pattern and form when there is not, which is the case you will most often be in with Imperial. That points you toward a likely maker, a plausible production window, and a starting point for comparing against documented Imperial lines, without needing to already know which of the letter marks you are looking at.

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