In 1928, Henry Kay Kuhrmeyer bought the Stromberg-Voisinet guitar company and soon renamed it Kay Guitar. Kay is known as one of the first manufacturers of electric guitars, which it began doing in 1928, but it also made mandolins. Because its electric guitars were far more popular than its mandolins, you may find it difficult to authenticate the age of your Kay mandolin.
Check the sound hole and head stock of the mandolin for a serial or model number.
Navigate to online guitar appraisers, such as usedprice.com or vintageguitarpro.com, and search the databases using the serial or model number to find your Kay mandolin. If you don't have the serial or model number you can still search based on the make of the mandolin.
Purchase a guitar appraisal book, such as "'50s Cool: Kay Guitars" or "Gruhn's Guide to Vintage Guitars," and search for your mandolin based on the serial or model number, or its similarity to other Kay mandolins.
Visit a guitar appraiser and take your Kay mandolin with you. If you're not comfortable taking the mandolin, take at least five photos of the instrument and write down all its key features; give this information to the appraiser to make the assessment.