second end the finished end was shiny and bright the holding unfinished end was black the black color indicated that rod underwent drawing operation which left oxidized black surface prior to inclusion testing black drawing oxide was removed by etching the etching solution consisted of hf hno 3 h 2 o in 1 5 20 volume ratio thirty six nitinol files were tested files were submerged vertically in 6 aqueous solution of sodium hypochlorite in glass vessel in room temperature around 25 u00b0 c for period of 24 hours submerged files were visually observed nonstop during the first two hours after first two hours files were checked every hour results in first 15 minutes corrosion reaction started on the unfinished surfaces of six separate files black flocculent started to ooze from the corrosion reaction sites after 24 hours no more files started to develop corrosion among six files which started to corrode in first 15 minutes of exposure four of them ceased to corrode and two still underwent corrosion when checked after 24 hours none of thirty six files tested developed corrosion on grinded working cutting end during 24 hours checking ready to use commercial nitinol endodontic rotary files for surface inclusions brand ii fifty four files were tested they were partially only working ground end submerged in 6 naclo in glass container for two hours in room temperature around 25 u00b0 c for two hours and constantly observed results four files started to corrode each one in only one localized place in first 15 minutes of submersion black flocculent oozed from corrosion places after two hours of submersion three files ceased to corrode and fourth one underwent further corrosion.