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Greyish white deposit on tin plating

I am using a tin acid bath with 120cc/L of sulfuric acid for plating of small steel terminals. I get a bright finish on the outside using a voltage of 4-6 volts but the internal surface seems to be dull in places with a whitish gray deposit. If I scratch it off I find that the residue is covering a bright tin layer. Is there any way to remedy this problem? I am using a rack plating method.

Nadeem Akhter
Sanemca - Lahore, Pakistan
2001

Sounds like a brightener film which you might remove by a post dip in the alkaline cleaner.

Tom Pullizzi
Falls Township, Pennsylvania
2001

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