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Art Glass Terminology

There are various ways to describe art glass of the past.  Collectors and makers use many terms to relate pertinent information about the product.  These terms may not be known to you yet, so RetroArtGlass will provide a quick lesson.  The descriptive words and their meanings are used in the RetroArtGlass catalog and will be helpful in understanding the art glass objects offered within

Methods of Forming Glass
Glass makers use many different methods to produce the final art form. The most common methods:

  • Hand-blown - Glassmakers use mouth and a blowpipe rod to blow hot glass into form. Hand blown items do not have seams (mold lines) and usually have pontil marks on the seat.
  • Mold-blown - Hot glass is blown by mouth into a mold. Mold blown items often are removed from mold then stretched and/or hand tooled for the finished effect. Mold Blown items usually do not have visible seams, nor visible pontils.
  • Pattern-molded – A gather of hot glass is poured or blown into a mold, then pressed and cooled before the mold is removed. Molded items often have apparent seams. Higher quality molded glass will have mold lines (seams) polished out or smoothed to invisible or nearly invisible.
  • Free form - A ball of hot of glass (the gather) is manipulated by hand or tool. The result is usually a thick, free flowing, modernist form.
  • Lamp worked – Using a torch flame to heat small gathers of glass while maneuvering it by hand and/or tool into desired form. Used for small delicate figurines, applied glass décor, ornaments, etc.  
  • Slumped – Cold glass panels are placed on a slumping mold and slowly heated.  Gravity causes the melting glass to flow down into the mold.

Pontil Mark - Normally located on the seat of the blown glass form. A pontil mark is the spot where the glassmaker separates the rod from the finished form. There are six (6) distinct styles of pontil marks:

    1. Ground Pontil - The rod mark is polished out by hand or machine. A ground pontil is usually roundish and a bit concave. The smoothed surface will have a polished effect.
    2. Soft Pontil - The rod and glass are separated while still hot. The small amount of leftover glass is left on the finished form and allowed to cool. The cooled "dollop" of glass is small, usually has a swirl, and is soft to the touch.
    3. Hard or Rough Pontil - The rod and glass are separated after cooling. The separation point resembles broken glass. Can be sharp and rough to touch.
    4. Stamped Pontil - Rod and glass are separated while still hot. Glassmaker uses a stamp to impress the "dollop" with a design or pattern. Often the glassmaker leaves a mark that can be recognized as the maker's mark.
    5. Cut and Polished - Many art glass forms will have no pontil mark or mold lines. Some glass forms are sheared off at the top or bottom and then polished.  The pontil mark is removed when sheared. A highly polished rim on a vase or ring on the seat is an indication of cutting and polishing.
    6. Pontil mark on base with mold lines on body – Blown from mold.  Glassmaker uses a rod to hold hot glass taken from a mold and then blows it out to desired shape.  Sometimes the mold lines are polished out, but often traces of the mold lines can be seen. Traces of a pontil mark on the seat can also be present on mold blown glass.

Types of Maker Identifications.
Glass makers use a variety of methods to identify the company or artist that produced the art form. Most common is the Maker's Label. Unfortunately, labels are often removed.

  • Maker's Label - An identifying label or sticker attached to the glass form.
  • Etched - Using tools, by hand or machine, to engrave the maker's logo or name.
  • Sandblasted - Abrasive material and a stencil used to create a frosted effect, in the form of the maker's name or logo.
  • Stamped - A stamp is used to impress the glass maker's logo or name; or an identifying design, on the glass form before it is cooled.
  • Embossed or Impressed – Makers identifying mark is pressed into to the glass while hot.  These marks are found on the center base of most everyday use glass.
  • Hidden – Some makers use a hidden symbol that identifies the artist or the glass house.  Usually hidden within the décor.

Glass forms are decorated in numerous ways.  Most often glass is used to decorate glass.  Below are a few examples of decoration techniques.

  • Hand Tooled - Glassmakers use of tools to enhance the design.
  • Applied - Blown, stretched or tooled hot glass is applied to the main form to achieve raised decorations, and/or attached handles, and/or form lips, etc.  Applied decoration uses glass to decorate glass. Some common names for applied decoration are "Prunts" (blobs of glass), "Rigarre" (ribbons of glass), and "Threading" (fine lines of glass).
  • Molded Ornamentation – Iron, brass, wood or clay molds with a pattern or design cut on the inside. Molds can be of 1, 2, 3, or 4 parts. As a rule of thumb, the more parts to the mold, the older it is. Not always true as reproductions are often made from the same mold. Also called "Cast Glass".
  • Crackle glass - Hot glass forms are immersed in liquid and then reheated to create a "crackle" in the glass.
  • Seeded - Maker intentionally "seeds" the hot glass with inclusions to create an antique effect or simply for decoration.
  • Controlled Bubble - Maker intentionally adds air bubbles in the glass to create a scattered, stylized or patterned bubble effect.  Often called bubbly glass, foamy glass, bullicante (Italian) and/or ariel (Scandinavian).
  • Iridescent - Glowing rainbow effect achieved through the glass recipe  
  • Carnival - Type of iridescent glass with multiple hues including metallic. The carnival effect is usually produced during a final heating process.
  • Hand Stretched / Pulled - The glass is stretched by hand or tool. Sometimes called "Free Form"
  • Stretch Glass - A unique effect of satiny, multi-hued iridescent. Achieved through the glass recipe and stretching technique.
  • Ribs - Ribs are made by the mold process. The mold has inner ribs of vertical, horizontal or swirled lines.  The maker often blows out rib molded glass to enhance the décor.
  • Optic Panels – Optic reflections called diamond optic, panel optic, coin optic, wave optic, and more.  Often produced by blowing out rib molded glass.
  • Etched - Maker uses hand or machine tool etcher to engrave pattern or design.
  • Enameled - Painted decoration, usually applied before glass is completely cooled. After decoration the glass is reheated to fuse the enamel to the glass.
  • Flashed - Designer uses a film or spray of colored glass, or metallic recipe to cover the finished form.  It is then reheated to adhere.
  • Murrina / Murrine - Bits of colored glass used to create mosaic décor. 
  • Avventurine (Italian) - Usually spelled “aventurine”. Small bits of gold, copper, silver and sometimes brass embedded in the glass. Produces a metallic veil decor.
  • Cut - Designer uses a hand or machine tool to cut away the glass.
  • Cased - Layers of glass are blown together.
  • Overlay - Cased glass is cut back to reveal layers beneath.

Condition Remarks - When buying art glass, it is important to know its condition. Never purchase glass if the seller does not provide condition information.  It is essential that you understand exactly what you're getting!

  • Excellent - In unused, or like-unused condition. Some glass forms may have been used but cared for so well that they appear unused. Normal "Bottom Wear" (see definition) is acceptable on glass items described as in excellent shape.
  • Great - In slightly used condition. Looks "Almost Like New". May have nearly invisible scratch marks, or minimal smoothed “chiggers” (see definition).
  • Good - May have a chigger or two or visible scratches that are unnoticeable without close inspection. 
  • Fair - Visible Problem. Chip, Crack, Staining. Worth buying if it's a bargain and can be repaired.
  • Poor – Irreversible stains, embedded calcium, severely worn décor, major cracks and chips. Not worth buying
  • Bottom Wear - Normal, expected wear on the seat of the glass form. Bottom wear often helps indicate the age of an item and does not detract from it's value.
  • Unintentional Inclusion - Unintentional foreign object(s) in the glass. An unintentional inclusion is a "maker's miss" and can be a trapped air bubble, a speck of charcoal from the furnace, unmelted raw material, a burst bubble on the surface, etc.
  • Intentional Inclusion - Some inclusions are meant to add to the form's decor. A "Controlled Inclusion" is an intentional foreign object in the glass.
  • Straw Mark - Slight wavy lines left on the form after cooling. The term "Straw Mark" comes from the old style of placing cooling glass on straw. Often an indicator of age. Depression glass is full of straw marks. Straw marks are also found on some more modern hand blown forms and are the result of the maker's cooling method.
  • Maker's Miss - An error on or in the glass form caused by the maker.
  • Sick Glass - Glass that is so badly marked with calcium deposits or clouding that it is impossible to remove. The chemicals or elements that caused the staining have actually imbedded themselves into the glass. Calcium deposits are usually caused by allowing water to evaporate off the glass. Glass should always be dried thoroughly when not in use.
  • Clouded - A thin whitish film that adheres to and discolors the glass. Usually caused by introducing glass to very hot water and harsh detergent. Never put good glass in the dishwasher!!! Usually the "Cloud" cannot be removed.
  • Condensation - Occurs in blown hollow forms when moisture laden air is trapped inside before sealing, or seeps inside through an unintentional breach of the seal. Also occurs and in stoppered decanters, cruets or jars when stored empty, but not dry. In hollow forms, a very small amount of moisture in the air condenses, causes a cloud that will never dissipate.  In decanters, condensation can form calcium "lace", (very fine web of calcium deposits) and is nearly impossible to remove if not caught early. Container glass must be thoroughly dried before storing with the stopper or lids in place.
  • Chigger - Very small rough spots that can’t be seen under normal viewing conditions, but can be felt with fingertips. Usually found on older glass items that have been used. For example, chiggers are usually found on the rims of spooners where spoons have rested. Chiggers on very old items do not detract much from the form's value because they are expected. Chiggers from use can help identify the age of an item. Remember, if it's called a "Chigger", it must be rough spots that cannot be seen unless closely inspected, but can be felt with your finger tips. A small chip cannot be described as a "Chigger". Chiggers that have been sanded are called "smoothed" chiggers, removing the roughness.
  • Chip - Visible piece of the glass has been broken off the form. If the chip is small enough, it could be repaired by sanding and polishing, but a seamless repair is difficult. Chips found on decanter's "stopper" neck are extremely common and more or less accepted. Rim chips may require qrinding which could reduce the size of the vessel, the same applies to bases. A visible chip negatively affects the value of a form.
  • Sliver Chip - Occurs when glass is placed on a hard surface, or bumped by a hard surface with too much force. Sliver chips usually occur on the seat of the form. A sliver chip on the seat is a bit common in older glass and does not detract much from its value. A sliver chip on the form's seat is not a serious problem, cannot be seen when displayed, and is usually very small and very thin.  Sliver chips elsewhere on the form, on a rim for example, even though they are small and thin, are a more serious problem. Sliver chips on the form should be professionally smoothed by grinding and polishing. Sometimes polishing will result in the sliver chip "disappearing" unless examined closely.
  • Crack - Glass cracks from stress (cold or hot temperatures) or by carelessness or accidents. Do not purchase cracked glass unless the item is extremely old and you are willing to have it professionally repaired. It will always bear the scar of the crack.
  • Repair - A chipped, chiggered or cracked glass form that has been professionally repaired by any or all of these methods; 1. Reheating 2. Sanding/Grinding 3. Polishing 4. Adhesives 5. Applying. A "repaired" glass form will have lost some value. If the repair can make the problem nearly invisible to the eye, the value loss is not as bad.


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