Defining the difference between crystal and glass is not an exact process. While is it true that all crystal is also glass, only certain types of glass can be properly identified as crystal. Outside this rather broad statement, however, there are not any ironclad rules that are universally invoked as part of the process of defining what constitutes crystal. Across the globe, there are different standards that are employed in various countries around the world that determine if the quality and lead content of a particular substance can be properly classified as crystal or if the item should be identified as glass. Even within some countries, the qualities that must be present in order for glass to earn the title of crystal may vary.

The lead content of glass is usually a determinant in the classification of finished goods as either crystal or glass. In the European community, glass items that have more than 4 percent but less than 10 percent of lead monoxide usually earn the designation of glass. While this is not always the case, glass that is found to have a lead content of 8 to 10 percent is granted the status of lead glass. Glass goods with a lead monoxide content of between 10 percent and 30 percent earn the designation of crystal. In the event that the lead monoxide content exceeds 30 percent, the item is often identified as lead crystal.

In the United States, a lead monoxide content of 1 percent is sufficient for glass to be classified as crystal. In other countries around the world that do not adhere strictly to the standards used by the European community, the range of lead content required before glass can be identified as crystal may range from anywhere between 3 percent to 15 percent. Glass with a higher lead monoxide content would be classified as lead crystal.

Both molten crystal and molten glass can be used to create beautiful and somewhat fragile pieces. Among the items constructed with molten glass and crystal are holiday ornaments, decorative figurines, delicate picture frames, and other items that are crafted with a great deal of detail. Crystal in all forms is considered to be especially desirable when it comes to dishware and drinking wear, as well as carefully crafted flower vases.