Copy Cad still coming out dull grey

[seanc]

Originally Posted by MikeDinWP

… But after showing some of the bolts and such to car friends… the bolts darkened where they were touched. Is it advisable to dip them in Blue Chromate to protect the finish? I assume that the shorter the dip time, the least “Blue” the chromate adds to the bolt surface, since I don’t want my bolts to be “Blue”.

Mike:

Yes, the parts need to be protected somehow. Raw zinc is a very reactive metal. It will corrode rapidly (producing "white rust", which dulls the finish), and will etch/discolor when exposed to any acid, even weak acids such as skin oils & perspiration.

Simplest protection is to apply a wax or oil coat, but it doesn't last very long.

Commercial parts are always passivated (given a "conversion coat"). Passivation could be an oxide (Caswell zinc "blackener), a phosphate (very rare), or chromate.

Chromates are far superior to the others both in corrosion resistance and longevity.

"Dip time" is a trade-off. Longer dip times produce more corrosion resistance, but if you want lighter colors, you need shorter dip times.

Sean