Get the best deals on Blue Cobalt Glassware when you shop the largest online selection at eBay.com. Free shipping on many items. Cobalt blue glass is also used as an optical filter in flame tests to filter out the yellow flame caused by contamination with sodium, and expand the ability to see violet and blue hues. Moderately ground cobalt glass (potassium cobalt silicate)—called 'smalt'—has been historically important as a pigment in glassmaking, painting, pottery, for surface decoration of other types of glass and ceramics, and other.
Cobalt blue is highly prized both as a pigment and as an unusual color for glass. In both cases, cobalt oxide produces the distinctive cobalt coloring. Most clear glass begins as a combination of a silica or sand, plus soda and lime. Glass makers add elements and minerals, such as iron or cobalt oxide, to derive different colors in the glass-making process. Cobalt is distinctive for its rich and deep intensity.
Other blue glass may be lighter or darker than cobalt and is often created by adding copper to the mix. Examine glass shards with a magnifying glass to detect identification marks that may be embossed on the glass. Some commercial products, such as Vicks, Noxzema skin cream and Phillips' Milk of Magnesia, use true cobalt glass in their packaging. According to collectors in the North American Sea Glass Collectors Association, pieces of those products wash ashore and are valued by collectors. Some collectors comb the beaches to add pieces of cobalt blue sea glass, which they believe to be the best type of sea glass they can acquire.