As part of preparation, a work piece should be thoroughly cleaned and fully demagnetized before Wire EDM operations. You should clean fluids, coolants, oils, and debris off all of the parts.  

Be sure to also clean any threaded or counterbored holes, because grinding grit and metal chips accumulate in these areas. These simple measures will prevent machining issues, extend filter and resin life, and avoid contamination of the dielectric water supply.