Batik backings- prewashing

I recommend pre-washing all backings, but especially batiks, for a few reasons.  Prewashing will soften up the fabric.  Unwashed batiks can sometimes cause skipped stitiches, and uneven tension, because it's hard for the needle to penetrate the fabric.  Prewashing really makes the batiks much easier to work with.  Another reason to prewash is to remove excess dyes.  Here is a great example- look at all that blue dye in the water!  Wow!  Without prewashing, all that dye is probably going to migrate to your top the first time the completed quilt is washed. 
It only takes a few minutes to run the sink full of lukewarm water, and swish it around a few times.  Repeat until the water runs clear, then spin out the water, and stick in the the dryer on low heat until the backing is dry, and you're ready to go.