perform the investigation, compare the rate of corrosion in at least two different acidic solutions and one neutral solution. Consider which acidic solutions to use.  The investigation should involve a fair test and all variables must be controlled to ensure valid results. The results could be recorded in a table and repetition could be used to increase validity. Non-passivating metals are metals that do not have a protective oxide layer that would prevent hydrogen ions reacting with metal atoms. Metals with protective passivation layers include aluminium, chromium, titanium and tin. Lead and copper objects taken from shipwrecks have been found to be corroded. Hydrogen sulfide produced by sulfate reducing bacteria can react with just about any metal except gold.