In the 1940s and 1950s, jadeite - a stain- and heat-resistant, milky-green glassware - was quite common and sold in hardware stores and five-and-tens. Sometimes a piece of jadeite would be included in a bag of flour or a box of oatmeal as an inducement to the consumer to buy the rest of the set. Today, jadeite is a popular - and valuable - collectible. A ball jug that once sold for $5 could sell for as much as $5,000 today.
McKee was the first company to mass-produce jadeite dinnerware in the '30s. The company's only complete dinnerware line is also the least popular today: the delicate and frilly patterned Laurel. You can identify McKee jadeite by the letters "McK" in a small circle on the back. The Jeannette Glass Company, however, actually coined the term jadeite. Most Jeannette jadeite is unmarked, except for some of the earlier pieces, which have the letter "J" in a triangle, followed by the mold number.
The Anchor Hocking Company produced Fire-King, a type of glassware that could withstand the high temperatures of ovens and stoves. "Jade-ite" was one of their most popular colors. Many jadeite aficionados collect Fire-King Restaurantware, a very popular and increasingly hard-to-find pattern. As the name suggests, it was made for institutional use in restaurants, hotels, and hospitals, and so is heavier than other makes, and much harder to break.
If you're interested in collecting jadeite, David Ross, a dealer of 20th-century glassware and coauthor of "Jadeite: An Identification and Price Guide," recommends examining each piece thoroughly for chips and cracks. Because jadeite was meant to be inexpensive glassware, there was no quality control. So you may notice that there are different shades of green, making it difficult to find matching sets. The good thing about jadeite is that it's very durable. You can wash it as you do any dish; keep it out of the microwave, though, as jadeite was produced before microwaves existed and is not meant to withstand that kind of heat.