tin pickup shown in graphs 7 and c are satisfactorily similar the graphs marked 4 and 21 2 indicating bare side wall margins of 40 mm and 25 mm height serve to show that greater heights of lacquer margin do indeed reduce the amount of tin available for pickup the graph denoted fl shows that a complete lacquer coating in the interior surface of the can substantially prevents pickup of tin in fig8 b shows that the pickup of iron from the wall ironed tinplate remained insignificant for the graphs denoted 4 21 2 and the control cans 34 c 34 however the graph 7 shows a surprising increase in iron pickup after 45 weeks this rise in iron content in the pasta is believed to have been due to exposure of damage to the tin coating arising at the more severely ironed side wall material it is interesting to note that the fully lacquered cans also give rise to pickup of iron a a margin of lacquer does limit the amount of tin available b the bare tinplate of the side wall must not be overworked particularly in the upper part of the sidewall after wall ironing it is usual to wash the cans to remove press tool lubricant from the surfaces of the cans the washing apparatus is sometimes used to apply a chromate treatment to the cans to repassivate the tin layer fig9 a shows results of actual tin pickup with time at ambient storage temperature for wall ironed cans made from the same tinplate as used to arrive at the graphs of fig8 a except that some of the cans tests had been subjected to the chromate treatment and some had not all the.