White layer on large pieces made from aluminium

I have a problem electropolishing and anodising large pieces made from aluminium (used to make cabinets bath). The final result is a white layer on the upside surface that I can't remove. I tried the sequence: Electropolish --> rinse ---> sodium hydroxide bath ---> rinse --> anodising ---> sealing.

And it seems that it works fine, but due to piece geometry is difficult to rinse properly after sodium hydroxide bath. I tried to change sodium hydroxide bath by 20% nitric acid bath, as usually works in chemical polishing, but I was surprised that it doesn't work at all.

The white layer is like a powder that it can be removed with oil, but obviously, I don't want to use oil at the end piece by piece. I would appreciate yours comments.

Dear Roberto,

Based on my experience it seems you have faced SEALING SMUT. To avoid smut look for sealing compound with anti smut property. hadi