Bay used an off white to white clay that did not vary much in color over the years. Sometimes you can finde a vase with a very light brown clay.

Bay used a two to four digits long form number followed by the size in cm. Some early forms use a letter in the form number. Some forms have the size in cm with one decimal ( ,5). Some pieces have only a form number. Early pocket vases and candle holders can be without a form number.

Bay reused form numbers over the years so it is not unusual to find very different pieces with the same form number. During the 70s Bay also used the same form number for a series of different forms. One example is the series 97.