The most reliable way to tell if a vase is antique is to get an appraisal on it. A qualified appraiser is trained to look for signs that other people miss and will give the best estimate of its age and fair market value. A written appraisal from a professional appraiser is required to insure an antique for its fair market value, and it is the only way to tell the difference between an authentic item and a professionally made replica or forgery. If an appraisal cannot be obtained or is not wanted, thoroughly research the specific item to learn specific signs of its age and condition.
A mark from the artist or manufacturer reliably tells the date of ceramic items such as vases, but these marks can be forged. Some vases are stamped with dates or item numbers that make determining their ages simple. Thorough knowledge of the vase's manufacturer also provides clues: colors, patterns and finishes used by ceramics manufacturers change over time and are useful in pinpointing when a vase was designed.
Look for signs of restoration or modern improvements to the item; many restoration techniques lower the value of an item. Antiques should be restored only by a qualified professional, and even professional restorations can have a negative effect on a vase's value. Appraise damaged antiques before undertaking any restorations to ensure they will not lower the market value.