Older crystal stemware can often be identified by the maker's mark, which is typically etched or embossed on the bottom of the stem. Some marks are faint and are only visible when the glass is held up to the light. Old marks also fade with time, and it may require a loupe or magnifying glass to read one clearly.
Once the mark on a piece of crystal stemware has been identified, it's possible to determine the stemware's source by checking for the mark in listing books. Various websites devoted to stemware patterns also provide assistance in identifying stemware. However, not all old high-end crystal stemware is marked. If company pattern records can't be found, older crystal stemware can't be identified.
Crystal stemware can also be identified by the specifics of its cut and stems. Certain crystal manufacturers recreate trademark elements in their stemware; for instance, Waterford crystal is known for its faceted stems and decorative cuts on glass bases.
Antique appraisers are also helpful in identifying crystal stemware. Some are willing to look at photos to begin the identification. Appraisers are likely to know the signature differences of stemware brands, including those from antique crystal manufacturers, and they have resources to research specific pieces of crystal.