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Physical Characteristics of Blenko Glass
Hand Blown Pontil Marks Thickness Rims Cold Work Color Transparency
Following is a simplified guide to identifying Blenko glass based on its typical physical characteristics. The only completely accurate way to identify vintage Blenko glass is by matching an item to a shape published in one of Blenko's annual production catalogs. All Historic Period Blenko designs are documented in these catalogs and they can be found on the Catalogs page of our website.

Hand Blown

Blenko glass is entirely hand made and hand blown by skilled workers, without mechanical intervention, as such it often displays characteristics unique to that method of production; chords (striations in the glass either in coloration or density), bubbles, tooling marks, etc. No two pieces of Blenko are exactly alike.

As with virtually all production glass, molds were usually used to establish the basic size and define the rudimentary form before the finisher (head blower) gave the item its final shape and details. The vast majority of Blenko's molds were hand-carved wood. Wood molds wear away; each use burns the mold making it lose shape and definition. Significant differences can be seen in the same design produced in the same mold early in the mold's life and late in its life. Mold lines are almost never visible on items made in a wood mold as they are spun in the mold; when viewed from the top all items blown in a wood mold are round. Therefore, any blown glass item that is round when viewed from above and has mold lines is not Blenko.

Only on rare occasion, due to prohibitively high cost, metal molds were employed. This would only be done for items that were produced in very large numbers, thus making the expense of the mold cost-effective. For example, the 384 "double-spout" water bottle was made in a metal mold and produced in the hundreds of thousands; by far its most widely produced item.

Approximately 10% of the company's production is cast and not blown, primarily bowls and decorative disks, which are solid and thick. For the most part these are inconsequential items that were cheap to make and easy to produce in large numbers, however, the high profitability of these and other simple items essentially subsidized the more experimental and advanced designs that were made in vastly smaller numbers.


Pontil Marks

A pontil rod (sometimes called a "puntee" or "punty") is the solid metal rod that is attached to the base of the still molten item so that it may be "finished" (also called "tooled" or shaped) after it has been blown and broken off of the blowpipe. When the item is removed from the pontil rod, a circular mark is left behind; this is called a "pontil mark."

Like other blown glass, the majority of Blenko glass has pontil marks on the base, which is only very occasionally polished. Other than cast items (which are not blown) very few Blenko designs will not have a pontil mark. See example images of pontil marks below, click to enlarge.

Blenko pontilBlenko Pontil AmethystPontil PlumBlenko Pontil Teal

Typically, the walls of Blenko vessels are quite thick; Blenko is rarely lightweight or thin walled. There is no simple or consistent way to quantify this though it is certainly not unusual to see rims that are 1/4" thick or slightly more. See rim images below.



The vast majority of Blenko's rims are fire-polished, meaning rounded and sometimes slightly uneven, an effect produced by briefly reinserting the item into the furnace to eliminate shearing and tooling marks after it has been cut from the blow pipe and shaped. See example images below (click to enlarge)

Left: fire polished rim still showing evidence of shearing or tooling marks
Right: smooth and even fire-polished rim

Blenko 5932 RimBlenko 5923 rim

It is unusual for Blenko rims to be polished/ground and that would only be done at the request of the designer and would be done consistently on a design - i.e. a given design would be exclusively executed with either a fire-polished or cold-polished rim (related: see next section "Cold Work" below).


Cold Work

Only rarely is Blenko ever cold-worked, meaning polished or cut after the glass has cooled. Blenko never did engraving. The most common type of cold work at Blenko would be on the rims as an alternative to fire-polishing, particularly on 1959 designs. The 964 horn vase is another noteworthy example of polished rims. See example images immediately below (click to enlarge).

Left: bevel polished rim on a 1959 design, bowl #5910
Right: #964L horn vase with detail of cold-worked polished and beveled edge

Blenko Beveled EdgeBlenko 964 Horn Vase

The underside of Blenko items are only ground if it is required to make the bases flat so that the item will sit level. As polishing the base added to cost, effort was made to avoid having to do this. It is important to note that Blenko did not polish bases with the sole intent to remove pontil marks; these were proudly left as evidence of being handmade.

Most Blenko decanter stoppers are cold worked; they are ground to fit. Both the stopper stem is ground as well as the interior neck of the bottle where the stopper sits. This is done to create a proper fit and seal. The grind is not polished so it retains a rough "frosted" look. See examples below (click to enlarge). There are some exceptions to this, particularly with post-1960 Architectural Scale decanters where sometimes neither stopper nor decanter neck was ground.

From L to R: stopper stem, ground inside of decanter neck, ground stopper inserted into ground decanter neck.

Blenko stopper stemBlenko decanter neckBlenko stopper and stem

The most immediate (but also the most subjective) way to identify Blenko glass is by color. For detailed information on this characteristic please see our Colors Page which includes comparative examples and a complete list of colors used, grouped by color range.



Historic Period Blenko is always transparent, never opaque or translucent. There is one exception to this: the Rialto Specialty Line, designed to have a translucent white body with contrasting ruby elements, made only in 1961. It is worth noting that on very rare occasions Tangerine and Jonquil, circa 1959, struck as somewhat opalescent or with opaque areas, although this was not by design and was random.

In the Late Period there are a few more instances of non-transparent glass, but again it is the vast minority.

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