Opalescent Glass Facts There are many misconceptions about what Opalescent Glass actually is. Opalescent Glass is any glass that has a milky white translucent area either on the edges, or as the pattern design itself. Opalescent Glass is a heat sensitive glass. The white color is achieved by reheating the glass at the furnace, a process called "Striking". The reheated areas of glass will turn white due to a chemical process caused by the reheating of the glass. The glass itself can be basically any color, but the Opalescence itself, is always White. You may ask why then do we have Blue Opalescent, or Green Opalescent, or Yellow Opalescent. The color Blue, Green, Yellow, and White refer to the base glass color itself. The Opalescent part is always White. It may have a Bluish cast to it, or a Greenish cast, but that's because it's picking up the base color of the glass. Today there are many different colors in Opalescent Glass, but the basic colors used during the Victorian era were Blue, Green, Cranberry, Vaseline or Canary Yellow, and White. White is the most confusing part. See (Opalescent Glass Colors). White Opalescent glass refers to "clear glass" that is Opalescent, that is to say, clear glass with White edges, or pattern design. It does not mean White glass with Opalescence. I'll state it again. White Opalescent glass is "Clear" glass with a white Opalescent edge or pattern design. Many early company catalogs referred to this color as "Flint". They used the term only to describe the color, which is "Clear". So you might hear "Flint Opalescent", or "Clear Opalescent", or "White Opalescent". They all mean the same thing. Keep in mind that this Opalescence is not enamel paint or any other treatment applied to the glass. It happens by a chemical reaction called "Striking". When glass is made, first a batch of material must be mixed together. Sand, Lime, Soda, and they add something called "Phosphate". In most cases it was ground up bone ash. This mixture is then placed in huge brick pots that are placed around a furnace. There were generally six pots per furnace. You could produce six different colors if you wanted to. If you add Copper to one batch you would get Blue glass. If you added Iron/Chromium, you would get Green glass. If you added Sugar, Iron, Sulfur, you would get Amber glass. If you added Gold, you would get Cranberry glass. If you added Phosphate you would get Opalescent glass. Also, dangers unknown at the time, if they added a material which contained Uranium, they would get Canary Yellow, or what collectors call Vaseline Glass. The mixtures in these pots are then fired in the furnace at 2500 degrees for 24 hours. They could do in twelve hours, and this was referred to as a day Pot. But usually it was fired for 24 hours. The following is the "Striking Process" A worker will go to the furnace with a long iron bar, and get a "Gather" of molten glass. Let's say he got glass from the Blue glass pot. Keep in mind the worker only sees a bright hot Yellow glow because it's 2500 degrees. He then takes the gather over to where the mould is on a table. He pours the molten glass into the mould. Another worker has special scissors and knows exactly how much glass to allow into the mould. He cuts the glass to stop the flow. A lever is then pulled down, and the top part of the mould presses the glass into the mould. These moulds are carved with a design pattern. The lever is raised, and mould pulled open, and the piece of pressed glass is removed. Now if the piece is set on a table and nothing else is done to it, then it will cool into a piece of clear Blue glass with a pattern design pressed in it. But if the same piece were taken from the mould and brought back to the furnace and reheated, then this first reheating is called "Striking". The piece is rotated in the furnace so that the heat will strike the entire surface. On bowl shapes the heat would only strike the edges. On Tumblers or Pitchers or Bottles etc., the striking would happen to the part that is closest to the heat. This reheating or Striking causes a chemical reaction with the Phosphate in the glass, and causes it to turn Milky White, or Opalescent. Remember the worker can't see any color except the bright hot glow of molten glass. It is his expertise that knows how long to allow the striking to take place. Too long, and the whole item would turn white. Too little, and you have only a very faint Opalescent effect. You may have seen some of these pieces that don't have very much Opalescence to them. There were primarily two types of glass that a worker would "Strike". One was glass with Phosphates in it to produce Opalescent glass, and the other was glass that had Gold in it. When striking glass with Gold in it, they got the Cranberry or Ruby color. Prior to 1921, the only way to get a Cranberry or Ruby color in glass was by putting pure Gold into the glass batch. Now you can imagine the process that took place to produce a Cranberry Opalescent color. Since the Chemical reaction only happens with one reheating, then several trips to the furnace are required to produce, let's say, a Cranberry Opalescent water Pitcher. Here's how it went: A worker got a gather of glass with Gold in it from the furnace. He would take it out and slowly spin it around only to allow the glob of glass to cool a little. He would then place it back into the furnace and Strike it to get the Cranberry color. He would then dip the glob of glass into a pot of clear glass with Phosphate in it and get a layer of that glass to coat the Cranberry glass. This is called Casing. He would then quickly bring this cased glass to an open pattern spot mould. This spot mould would put a raised pattern design on the glass. The mould was opened, and cased pressed piece was taken back to the furnace to strike the outer layer of glass. When the heat from the furnace strikes the raised area of the pattern, the pattern turns White from the Phosphate in that glass. The Cranberry will never get any darker because it was already struck once. Now the piece is brought back to the finishing mould. The ball of glass is blown into the two-part mould that will give the Pitcher its final shape. A handle is applied and the top of the Pitcher is crimped, and it is then placed in a cooling oven, which allows the piece to slowly cool. Only when the piece is cool will they be able to see what kind of job they did with Striking to get the beautiful combination of Cranberry and the White Opalescent pattern on the Pitcher. This is the reason no two pieces are ever the same. Some Pitchers have very beautiful deep Cranberry color with Bright White Opalescent patterns, while others have a very pale Cranberry color and pale Opalescence to them. It all depended on the worker who did it. Some were very good at their jobs, while some were not. This pretty much sums it up as far as how Opalescent Glass was made. There were a couple of other Opalescent glass colors that were made during this Victorian era, and these two other colors were Amber, and Amethyst. The earliest known Amber Opalescent color was made by the Phoenix Glass Company around 1885. Later by the Indiana Tumbler and Goblet Company beginning 1903 with their Golden Agate color. Amethyst was used early around 1908 by the Fenton Art Glass Company. Fenton's Amber color appeared in the 1920's. So if you find early Amethyst Opalescent pieces, they were more than likely made by Fenton. The patterns made in Amethyst Opalescent were "WaterLily and Cattails", Boggy Bayou, Blackberry, and Beaded Stars. There may be others. Company Assetts. The most important asset that a glass company could have was their moulds. Without them, they could not compete in the mass produced market of the time. Paying mould Carvers to carve the patterns in metal moulds was very expensive and companies soon realized that the more variety they could get out of one mould, the more profitable it would be for the company. What they did was use one pattern from one mould and create several different shapes using that same mould and were advertised as assortments. By flaring and crimping and changing color, they could create several entirely different items using the same mould. The following pictures illustrate a couple examples: Jefferson Glass Block pattern. At first glance, you might think these two items are two totally different things. They are. But look more closely. You'll see they are made from the same mould. Left to right: Jack-in-the-Pulpit ruffed bowl in an extremely rare Cobalt Blue Opalescent color and a Celery Vase in Green Opalescent with a Cranberry Frit edge. Jefferson Glass pattern Pearls and Scales Left to Right: Rose Bowl and Card Receiver in White Opalescent with Cranberry Frit edge. Northwood pattern Fancy Fantails Left to Right: Rose Bowl and Candy Dish in White Opalescent with Cranberry Frit edge. Click your back arrow