Brake caliper color

[links113]

Hey all,
Quick question about the proper color of these brake calipers as I have just started the rebuild for my 113_44.
I've been rebuilding ate calipers for almost a decade and for multiple different car manufacturers (porsche, alfa, Ferrari, BMW, and Mercedes) and they all use different colors lol I've seen on this website of people rebuilding their calipers and they do them in yellow zinc and then I've seen posts of people pulling NOS calibers out of an ATE box and they're clear zinc. One place and a lot of us the right of people get our parts (K&K) sells ATE calipers and on their site they're clear zinc. I've had multiple people tell me it's supposed to be yellow zinc but I'm under the impression that it should be clearing.
The front room said I pulled off of this mostly original 69 280 was clear zinc underneath the nasty black the day I painted the underside of the car in. So I'm under the assumption that it should be clear zinc. What's everyone's thoughts on that?

[wwheeler]

Using this assembly line picture as a guide, the calipers are yellow zinc. Can be seen clearly if you zoom in. I have a much higher resolution version and is easier to see. They may have dropped the yellow chromate in favor of the clear (slight blue) chromate at some point for who knows why. The other controversial point is the backside of the caliper on the rear axle. In this pic it appears to be black. Possibly caliper was on the axle when the whole thing was sprayed. Not sure about the front. I don't know, just what I see.

NOS or MB replacement parts are frequently NOT the correct plating finish or color as was on the line. Can't go by that. NOS parts could have been made years after the car was produced and even the designs change. Still function and fit, but look different.   

[Pawel66]

My 2 cents.

Please note that yellow zinc was stopped at certain point in time due to environmental reasons. I also am under impression that after several years yellow zinc stops to be yellow (it is just an overcoat on regular zinc coat if I understand correctly).

[mdsalemi]

There probably shouldn't be much of an environmental issue with any zinc plating, it's the CADMIUM plating that has the issues. And yes, the yellow color is a passivating reaction coating after the zinc (or cadmium) plating.

[Pawel66]

Yes, thank you, I keep mixing these types of plating.

[wwheeler]

As far as Mercedes goes, I would bet that all yellow colored parts are zinc. Cad was phased out at some point around the time Mercedes started using much more yellow chromates. When? Don't know. I have virtually no yellow chromated parts on my '60 220SE (W128). It is mostly black oxide and clear chromate - not sure if CAD or zinc though.

The color as Michael said is nothing more than a chromate that is applied after the plating process. It is a protective coating for the plating whether it be CAD or zinc. Zinc and CAD to a lesser degree, are susceptible to acid attack. The chromate adds a minimal barrier. All of these coatings do nothing more than to protect the base metal from corrosion. You do not have to have the chromate coating but it stabilizes and gives the plating a more uniform look over time.

Not sure if any particular chromate color is better than other. I do know the yellow is a little trickier to apply than others. I do zinc plating and personally have yellow, clear (slight blue) and black. The clear is what I call hardware store bolt color and black mimics black oxide.