AbstractA study has been nude of the effect of variation in coating thick‐ ness (from 2 to 13 02. per basis box) on the quality of clectro‐tinplate deposited from t i e stannous sulphate and sodium state baths, respectively. Using from two to ten specimens for each determintion, CUNCS have been obtained showing the influence of coating thickness on the thiocyanate, hot‐water porosity, humidity, and salt spray test VBIUCS, and showing the effect of time of exposure out‐of‐ doors on weight increment for a range of coating thicknesses. All of the tests reveal a deterioration in the quality of the deposits as the thickness diminishes. There is a certain minimum thickness, varying somewhat according to the nature of the test applied, below which this deterioration is npid. As estimated by the thiocyanate, hot‐water porosity, humidity, and salt spny tests this minimum thickness is in the vicinity of 12 02. pe