Introduced as Iridescent Ware in 1907, carnival glass acquired that name unofficially from collectors in the 1950s. This marvelous glassware acquired its nickname from the metallic layer on its outside, which constantly changed colors. Iridescent Ware was made in ornately patterned molds, and was sprayed with a mixture of metallic salts before it had started to cool, which allowed for the color-changing effects that gave the glass its fame.

Made as both functional and ornamental objects and found in a wide array of colors, carnival glass is an inexpensive pressed glass, often called dope glass by glass factory workers because of the process of applying the iridescent coloring, which is known as doping. Its production can be traced back to as early as 1907, with many, many different pieces in over 150 distinct patterns. It did not, however, command the expected prices, and was subsequently discounted heavily.

Translucent colors such as amethyst, marigold, cobalt, green, and red compose this glass, though it is also made in an opaque white referred to as milk glass. The glass was also made in semi-transparent or translucent pale green, and was called Vaseline or uranium glass; trace amounts of uranium salts were contained in the glass, which could produce a faint green glass glow in reaction to UV light. This was, of course, before the hazards of radiation were fully known and understood.

Millersburg glass Company is one of the largest producers of this kind of glass. Crystals were the first glass products of the company. But they decided to go for iridescent glassware to ride the wave of enthusiasm. So, during the early 1910, the line of Radium Glassware was brought out by Millersburg glass Company.

Carnival glass is a collector's item. Prices of these glasses vary wildly from a few dollars to thousands of dollars. Carnival glass has become antique glass collectible and there is a good active market for it.

The carnival glass is very difficult to identify. Unfortunately, most of the manufacturers avoid including a maker's mark in their product. Others did so only for part of the time they manufactured the glass. The process of identification involves matching of patterns, colors, sheen, edges, thickness, factors found in old manufacturer's trade catalogs and other known examples, or other reference material. Identifying this glass has become a challenge even to experts since many manufacturers produced duplicates of their rivals' popular patterns.

At the time of introduction in late 1907 the carnival glass was called as Iridescent Ware. However, people started using the name carnival only after collectors in the 1950s began to refer to it as such. Among the greatest producers of this type of glass was Millersburg glass Company in Ohio. The first glass products by that company were crystal however the Millersburg plant decided to follow success for iridescent glassware. There is a very active market for this item since it has become an antique glass collectible. So even for an experienced expert this is a hard task.