Parkerizing ...

[Michael G.]

Re: Parkerizing ...

For many years, GM used several finishes on its fasteners that were essentially three step processes 1) zinc phosphate substrate 2) paint dip-spin or electro-deposit 3) oil dip. These finishes are thin enough for fasteners, are normally black, and offer fairly high corrosion protection. The corrosion protection is far superior (three or four times more much salt spray protection) to zinc phosphate plus oil. This level of protection is certainly more than adequate to offer protection for a car that is rarely driven in rain or exposed to salt.

While I have not plated anything with them for a few years, I think most major platers can still do them. A plater would know the most common ones by their GM numbers as GM6047M and GM6174M.

[Ken T.]

Re: Parkerizing ...

Black chromate is darker than parkerizing but has to go over zinc, you get the protection and dark black coloring. It's acidic and eats in to the zinc, so you need a good zinc coating.

http://www.nulltime.com/zincplating/parts/bolts_and_yokes.html

[Chuck S.]

Re: Parkerizing ...

Black chromate is darker than parkerizing but has to go over zinc, you get the protection and dark black coloring. It's acidic and eats in to the zinc, so you need a good zinc coating.
http://www.nulltime.com/zincplating/...and_yokes.html

I knew a guy whose plant did black chromate on Ford's steel AC tubing components. (Ford took a different path on AC tubing components than GM, which pursued aluminum from the beginning. At the time I knew him, the rumor was Ford was developing an aluminum fabrication capability thereby ending his black chromate business.) The finished steel tubing components were first zinc plated, then chromated.

My observation was that the surface finish was smoother and shinier than phosphate, but that's probably a direct reflection of the substrate surface smoothness. It's an attractive finish, but it doesn't have the matte black look of phosphate; my recall is it's probably closer in appearance to black oxide.

[Steve L.]

Re: Parkerizing ...

I've been using Caswell black phosphate for natural parts and Caswell black oxide if I get parts from the vendors that are zinc plated but should be black phosphate.

The black oxide is a bit darker and shinier. I just can't get myself to strip the zinc on new parts and the black phosphate. The black oxide does get damaged a bit when you torque the part. I did this to the lower rear shock nut(the fat one). I think I could repair the damaged black oxide by wetting a rag with the solution and holding it against the nut for about 10 seconds. The solutions works really fast. I think a good judge can see the difference between black oxide and phosphate if he has enough light and can get close to the part.

[Alan S.]

Re: Parkerizing ...

Hi Steve,
Responding to your point about your seeing the difference between black oxide and the manganese phosphate.... I think the 'sparkle' in the sun or a fairly strong light source is a telltale for the phosphate finish. I believe the amount of oil coating added after the phosphating does cut down on the 'sparkle'.
Regards,
Alan

[Steve L.]

Re: Parkerizing ...

Alan, your referering to the real manganese phosphate. I don't think the Caswell black phosphating kit is real. It does blacken the bolts nicely but there is no sparkle.

I looked at and saved the info that someone posted on how to do the manganes phosphate. It looked interesting and not that complicated but did take a lot more effort with hot crockpots and boiling in well vented areas. The Caswell is at room temperature and only take a few minutes, then soak in their "sealer" which I think is just an emulsified oil. It is a lot easier and looks reasonable. After letting it dry overnight, I gave it a mist of satin clear since I don't think it offers very good corrosion protection.


One day I'll try the manganese phosphate, but right now I have my hands full with the body off resto, job, and family plus the other plating kits- zinc, yellow, black and blue chromate from Caswell and a plating identification kit from Koslow-all of which are fun to play with.