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From an experienced plater, the higher the voltage the faster it will plate yes but the adhesion will be weaker. If you are looking for a fast plating job the high voltage works but it may flake off in time. If you want something that is durable or needs wear resistance the half a volt should be used over a longer period of time. A good way to test the adhesion is to use a strong masking tape after it is dry. Press the tape on to the plating the pull it off quickly and the look at the tape, if you see plating on the tape it didn't adhere properly. Now you know:-D