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Glass is labeled and catalogued in different ways, including by its formula or chemical recipe, how the final shape is formed, its style and genre. The following are standard types of glass, defined by the formula, method and genre.
Pressed glass. Most glass items are pressed into a mold and are called pressed glass. This involves pouring the molten glass into a mold which forms the shape and outsider design. Most pressed glass has a seam, which is a thin line along an edge. The mold can produce various designs, patterns and even a pattern mimicking hand cut glass.
Cut glass is is glass that has the outer design cut by hand or by machine. This is considered fancy and more expensive glass. Cut lead glass, containing lead, is called lead crystal or crystal and is considered high end glassware. It is used to make fancy bowels, wine glasses and crystal chandeliers. Cut glass will not have a seam, as it is usually hidden or was never there one. The cut of the outside will be sharper than pressed glass made to resemble cut glass. Cut lead glass, or lead crystal, is very clear and heavy. Vintage American cut glass is called Brilliant Cut or American Brilliant cut.
cut glass bowl
Blown glass is an ancient form of glass making that is still used in the fine arts. The molten glass is formed by literally blowing it throw a tube. The resulting glass item will often have a blown look and glass varying in thickness. It will not have a seem. It often has a pontil or rod mark, where the pipe was attached. It will appear as a little hole or bump, though it is sometimes smoothed over. Blown glass can have tiny bubbles or shifts, and colors that mix together. Some may be assembled from multiple parts into one piece.
artistic blown glass fases
pontil mark on bottom of blown glass
Soda-lime. Most glass is soda-like glass. Soda-lime is the chemical makeup of the glass, and is made up of sodium carbonate and lime. It’s naturally clear, though not as clear as lead glass, and fairly hard. It can be made into many shapes and designs, from soda pop bottles and drinking glasses to fancy cut glass decanters. Soda lime can be pressed, blown or cut
Lead glass. Lead glass is made with lead in it, typically 10% or less. It is known for its sparkly brilliance and is used for much fine glass, including expensive wine glasses, lead crystal (cut lead glass), chandeliers. Cut lead glass, also known as lead crystal or crystal, is used to make rhinestones and fake diamonds. As it blocks more ultraviolet, infrared and other lights, it is often used for science and medical labs. Lead glass is heavier than soda-lime glass. Lead glass can be pressed, cut or blown.
Borosilicate glass (Pyrex). Commonly known by the brand name Pyrex, boroilicate glass is a specialty glass used to make heat resistant items, including cooking ware, oven and microwave windows. It is made from the same formula as soda-lime glass, except is tempered through a second cooking. Looking at the glass itself, it’s difficult to tell the difference between Pyrex and soda-like glasses, so you have to look how its used. Also ‘Pyrex’ on the oven dish will identify. Old Pyrex cooking ware is popularly collected.
Uranium glass (subcategories vaseline glass, custard glass, jadeite glass). Uranium glass is a highly collectible antique glass that was made with uranium salts. Uranium salts are naturally a bright yellow and they were used to color the glass. Uranium glass ranges from yellow to green, with the green versions having had additional coloring chemicals added. Uranium glass is transparent to opaque and comes in many forms and styles, including plates, glasses, cups and saucers, salt and pepper shakers, candlestick holders and figurines.
As it contains uranium, the glass is radioactive. Happily, the uranium salts added and radiation given off is so low it’s considered harmless.
Uranium glass is identified by its general appearance and color (yellow to green) and because the uranium salts makes it fluoresce a bright green under black light. Some advanced collectors and dealers even use a geiger counter to measure the radiation, but for most people a black light is more than enough.
There are sub categories for uranium glass. The problem is different people use the names differently, even sometimes applying them to non-uranium glass that has same superficial appearance. Some areas of the world use the terms differently.
The following are common subcategories.
Vaseline glass is a nickname given to uranium glass that is transparent and with a yellow or yellow-green tinge. It got its nickname as some thought it resembled vaseline. However, some call any kind of uranium glass vaseline glass, some say vaseline glass can only be yellow and some call any kind of transparent yellow glass vaseline glass even if there is no uranium salt content. Some collectors and dealers label that syrup pitcher vaseline glass, while others would not because it’s not yellow. The latter would call it simply uranium glass.
Custard glass is a uranium glass that is an opaque or near opaque yellow. Though some some call any opaque yellow glass custard glass, even if it contains no uranium.
Jadeite glass is uranium glass that is opaque or semi opaque pale green. However, some call any opaque or semi opaque pale green glass jadeite glass even when it has no uranium content.
With all the competing subcategory definitions, just remember that a black light will tell you if something has uranium salts in it and is genuine uranium glass.
cobalt glass is a popularly collected glass that uses cobalt salts to create a deep blue color. Cobalt glass has been made for centuries and centuries.
cobalt glass is easy to identify due to its blue color
Cranberry glass, sometimes called Gold Ruby and Rubino Oro, is a red glass made by adding gold oxide to molten glass. The glass is expensive and used for high end items.
Milk glass is an opaque to translucent glass that is usually milky white but can be made to be milky blue, pink, brown, black and blue. It is used to make glasses, cups and other glassware. It was also used to make the scarce opalotype photographs, which had the photographic image on a pane of milk glass.
blue milk glass
1800s opalotype photograph on milk glass with metal foil frame