Belford, Please confirm that it is H2So4 added to H2O2, instead of H2O2 added to H2So4, which might be dangerous. Good luck, Hongjun Zeng MEMS/Nano Scientist Microfabrication Application Laboratory(MAL) University of Illinois at Chicago -----Original Message----- From: Sumant Sood Subject: RE: [mems-talk] About the Piranha cleaning Zhiwei, For Piranha, I add 1 part of H2O2 (30%) to 3 parts concentrated H2SO4. The reaction is exothermic and the solution heats up for the first few minutes. Once the solution cools down, you can heat it upto 130 deg C for cleaning.