I have used batiks that are so thin they cling to the next one in the pile and two pieces get sewn in place. As long as both stay put when you add the next piece ...not even the quilt police would detect the error. I would suspect just a quick spray of starch would be helpful when ironing the two together? I have found that many batiks have some of the residual wax used in creating the design in their weave and a hot iron seems to bond two as if they were one.