In its truest form Batik is a technique of wax-resist dyeing applied to whole cloth, originating in Indonesia.  The pattern is made by drawing dots and lines of the resist with a spouted tool called a tjanting.  This process has been transformed here using multiple layers of contrasting glass powders.  The patterns resulting from that cannot possibly be duplicated exactly.
The movement of the powder layers on the glass as the design is created outside the kiln, as well as the sometimes-unpredictable nature of firing glass to well over 1450 degrees, leads to pieces that are truly one-of-a-kind.