1 Reply Latest reply on Jan 14, 2016 1:41 PM by Mark Gebert

    Removing tin from tin plated cast iron

    Peyton M

      Hi,

       

      I've been searching high and low and have not been able to come up with a conclusive answer to this issue. I have an antique meat grinder that is of cast iron construction and was originally "tinned".  The tin coverage is somewhat spotty after 100 years or so of wear, and the integrity of the tin coating on the iron is questionable at best.  I wish to put the grinder back into service at home and don't wish to poison those who partake in my food with flaking tin(didn't it use to have lead in it?)  I would like to remove all of the existing rust, general gunk, and tin if possible and replate the grinder with fresh pure tin.  Now if the replating is tough or ill advised, then I'll look into other options for coating the cast iron.  I may even choose to leave it bare and just oil it. 

       

      Back to the stripping.  I have read that soaking cast iron in a sodium hydroxide solution is a great way to clean it up and strip it back to bare metal.  Is that true? Would that also remove any traces of the old tin plating?  I've also read about using electrolosis with the sodium hydroxide solution with the cast iron part attached to the negative electrode and the postive electrode attached to some scrap steel. 

       

      Anyway, I don't know what way to go and would love some input from folks that know the world of chemistry.

       

       

      Thanks,

       

       

      Peyton

        • Re: Removing tin from tin plated cast iron
          Mark Gebert

          The toxicity of lead has been known for centuries so I would be very surprised if a tin coating was alloyed with lead for something known to have food contact (meat grinders, linings of food cans, etc.). 

           

          In terms of stripping the tin from cast iron, this can be done with either mineral acids or alkali but alkali's are more selective towards the tin with the mineral acids attacking both the tin and the iron.  There are other components added to commercial alkali based stripping solutions such as chelators which improve the strippers performance.  For this reason, I would use a commercial based stripper such as the one made by Metalline Corpooration.  I have enclosed a link to their product below:

           

          Tin and Tin Alloy Strippers

           

          Mark Gebert