[KCV6]

Sounds like there is insufficient agitation to remove hydrogen bubbles that are forming on the lower surface. I would try increase the amount of agitation or hang the parts in such a way that there are no flat surfaces or "bubble catch" areas paralell to the bottom of the tank. The agitation has to be vigorous enough to detatch any bubbles that form on the item but random enough to make the agitation of the solution uniform accross the whole piece. i.e. no points where a hard jet of bubbles or solution movement is concentrated on one part of the piece being plated.

A second option is to regularly shake the part to detatch bubbles. This unfortunately means someone has to constantly be hands on with the process.

I run air into the bottom of the tank so bubbles flow from the bottom to the top and also run a plating solution pump (if required) directed so the tank is stirred.

Cheers

Mark Smith