Dummying Tanks before Starting electroplating

Dummying is the common term for dummy plating, or using a scrap piece to plate, usually at lower or higher then normal current densities.

If you were constantly nickel plating zinc or copper or brass parts, you would frequently dummy plate the bath at low current densities to PREFERENTIALLY remove the copper and zinc.  Normally, the dummy has a large surface area, to maximize the amount of material removed.  In my experience, a large piece of corrugated sheet metal is used with a current density close to 5ASF or lower.

There are other uses for dummy plating.  In a hex chrome bath, it can be used to remove chlorides and activate the anodes.  These dummies are usually very small to prevent the buildup of tri chrome.  You can also perform a high-current density dummy plate to remove excess brightener.

A separate dummy tank is usually one that is used to perform the dummying in.  You can also do a continuous dummy, where you use a small tank with a separate rectifier, anodes, and dummy panel to perform the dummying continuously.  Usually, you pump the solution into the tank, which is higher in elevation than the main tank.  As the dummy tank fills, it overflows back into the main tank.  Many platers use them in high-production shops to minimize down time.

One thing to consider with the current price of nickel.  While dummy plating targets a certain contaminant (usually), you are still plating a majority of your normal metal.  That is to mean, in a nickel bath, you can try to dummy out zinc, but the majority of the deposit on the dummy panels will still be nickel.  The zinc content will be higher than on a normal deposit, but it will still be mostly nickel.