than a conventional hno 3 solution this is important because less zinc is introduced to the plating solution this example demonstrates that less zinc is deposited on the substrate to be metal plated when using the double zincate method of the invention as compared to the conventional double zincate process cz 46 aluminum alloy disks were treated using steps 1 4 of the procedure of example i one group of the disks were randomly selected and immersed in a conventional hno 3 solution 50 by volume for 1 minute at room temperature the other group were immersed in a 50 by volume hno 3 solution containing 0 5 g l ferric ions supplied as ferric chloride for the same length of time and temperature the disks were then immersed in a second zincate bath as in step 6 of example i for either 10 20 30 40 50 or 60 seconds at room temperature the zincated disks were then stripped in 50 by volume hno 3 and the amount of zinc deposited on the disk determined by atomic absorbance spectrophotometry fig4 shows that less zinc was deposited on the disks when using the method of the invention as compared to the conventional double zincate method this is important because there is less surface disturbance and consequently a thinner but denser coating of zinc is obtained the iron apparently acts as an inhibitor thus retarding and thereby controlling the dissolution of aluminum by zinc furthermore the thinner deposits of zinc will not contaminate the subsequent electroless nickel bath as rapidly aluminum 5586 alloy disks were comparatively plated using the procedures of example i.