Bay always used white clay and marks are almost exclusively moulded. Many items are marked “Bay” which allows easy identification.
Other distinctive elements of the base markings are that the separation of West and Germany is sometimes done with “.-“.
Another good identifier is that that the “y” of Germany has a curly base; this is very unusual amongst manufacturers and a good indication (but not conclusive evidence) that an item may be produced by Bay.
The form numbers used by Bay are in the range 1 -1100’s. The height is usually separated from the form number by a “-” or space, and is always indicated in cm. Occasionally numbers are on two lines, usually indicating an earlier item or a lack of space on the base.
A number of Bay items can still be found which retain their original labels. In some cases these can be used to provide an indication of when a vase was produced.