White residue on the blued parts

After the bluing (black oxidizing) and assembling of the parts we observe after a while (1 week) there is white residue, mainly on the joint points (screw) of the part.

Do the parts have to be blued as distmantled (as unique part,i.e. not as assembly) ? We're bluing the parts with their screws.

Or is there something wrong with boron oil mixture(with water) that is used to clear part after bluing.

What do you suggest about the water displacing oil ? Do we need to put an additional bath full with hot pure oil following the boron oil bath ?

The white salts are bleeding out after the oxide process. It is very difficult to completely rinse the chemicals out from processing. Oxide the parts separately, then assemble.