Using Caustic Soda to Put Finish on Aluminum Parts

Hello, I am trying to put a good finish on some aluminum parts and do not know much about what I am doing. I have been playing around with NAOH solution to eat away mill marks on pieces. When doing this I found if I let the parts sit for a long time and rinse the smut off and let bathe for more time, it would bring out a really cool effect of the extrusions of the 6061 aluminum. However my problem is that this is time consuming, if I let sit to long the smut will not come off. It has also been an issue that the pieces will get oils and dirty after they have sat from being in the caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] . How can I prevent that? My goal is to pull out the extrusion lines that look really cool, then put back on the mill and put some shiny finishing edges on the piece before painting with a clear coat. Does anyone know of another way this can be done more effectively?

Thanks,
Jack