Strange! Suddenly have to plate MUCH longer for same thickness

Hallo,
I should like an opinion on a situation which has developed just recently in our plating shop. We plate zamak, starting with cyanide copper, then nk, etc.
We used to plate for about 40 mins up to an hour, or so, with barrel plating, to get a good, shiny finish, but just recently we have had to increase times up to 1.40 mins (min.). The bath is pretty new, and has no noticeable contamination.
Does anyone have an explanation for this? Could the zamak alloy have changed and be absorbing more nk?

Thanks,

Hi Rupert,
Seems to be that you need to know which chemical that causing you the delay. From my experience, normally copper cyanide can develop the carbonate quite fast which may restrain your anode to dissolve and causing your copper bath conc. to drop. is there any light yellow to green film on your anode. if there is the anode polarization is occurring. this may due to insufficient anode surface. try to increase the anode surface which may help you to eliminate the anode polarization.