There are many kind of metal preparation before this metal being plating using chromium plating. If this metal have plate by nickel for example, there is not too much treatment before chrome plating, if no delay after nickel plating it just dip in acid and then rinse by water may enough, but if the part have been keep for long time and have treated by other process like buffed, further treatment is needed to get better chromium plating.
To see the detail of this preparation process on electroplating can see on here: Plating Preparation, preparation for plating itself will involve a chemical treatments, that need of certain chemical with certain composition and should be do in order as the guideline on this chromium preparation of base metal. Beside of must follow the order of chemical treatments also need certain time to result good cleaned and ready for further process.
To see the detail of this preparation process on electroplating can see on here: Plating Preparation, preparation for plating itself will involve a chemical treatments, that need of certain chemical with certain composition and should be do in order as the guideline on this chromium preparation of base metal. Beside of must follow the order of chemical treatments also need certain time to result good cleaned and ready for further process.