Galvanization (passivation) color grey green

[mbebrim]

What you say about this color?

[Peter]

The yellow color looks good, but far as I know where most of the parts you show not yellow but blue (= shiny aluminum color) or the hood closing mechanism even black.

Peter

[Figoulu]

I mean... It's like mine 

[SEB]

If you have the necessary know-how- you can get also the coating in nearly gold color- (Parts from a R18 Fuel Injection Pump)

[mbebrim]

They are galvanize in dull green color as original.

[SEB]

I remember my disappointment when I was galvanizing parts for the engine of my W111 Coupe. As result of the galvanization I got all the colors of the rainbow. I was not happy with this, so I decided to chrome it.

Later I learned, that this was a sign of bad quality. Now I have a specialized workshop, who is doing the parts only for oldtimers and they deliver the parts in a nearly gold color. I am happy now.

[mbebrim]

I had no problem installing the refurbished galvanized parts in yellow. I galvanize parts with six valent chrome passivation what making them nice yellow. But I noticed that the original parts are not yellow passivated, but passivated in gray green. Galvanizing these parts to obtain the desired color tone was a big problem. See in photos what I mean.

[mbebrim]

Some photos of installed parts.

[mdsalemi]

Perhaps a language or translation issue, but this is not galvanizing. It is zinc plating. Galvanizing is dipping parts in molten zinc.

Some of the parts you plated in zinc were originally cadmium. Some cadmium plated items had the yellow or gold phosphate wash and others left the natural cadmium silver color.

[mbebrim]

Maybe I'm not exact in the definition because English is not my native language. https://en.wikipedia.org/wiki/Galvanization
We use the electroplating with chromate conversion coating for surface passivation. Uh.
But the topic is about the green or gray-green color of some Mercedes original parts and how to get them.

[SEB]

But after few years I noticed, that the surface is not any more so shiny. So if here are some experts in zinc plating my question is how protect the surface? Or what to do to keep the surface longer so shiny?

[mdsalemi]

But the topic is about the green or gray-green color of some Mercedes original parts and how to get them.

Yes, as mentioned--a language and translation issue.

When I have had parts plated, they have provided a choice of coloring in the secondary process of adding the "phosphate wash" or passivation.

However many of the "gold colors" that you will get with that of zinc do not look exactly the same as that of cadmium. I never was told of any gray/green coloring on metal parts, just on the "silver" and "gold" colors.

[Leester]

To Sebastion's last question, how to keep the gold color from turning grey, I have had parts cadmium plated, then sprayed a clear coat of Nyalic on them.  Some parts haven't even been installed yet so there hasn't been enough time to determine if the Nyalic will serve to retain the gold color.
As pointed out, the gold is a wash and I believe both the wash and the cadmium plating will naturally turn grey over time (unless hopefully protected with the clear). This turning grey is part of the natural oxidation process and is what provides protection to the underlying metal.
I was disappointed that spraying the Nyalic clear did away with the "rainbow" effect. So if you want to keep that effect, I would not apply a clear. But of course, you will lose the rainbow effect over time anyway.

[wwheeler]

Parts that are plated in either zinc or CAD and left bare, will all fail slowly over time and faster when exposed to acid. The colors we see (yellow, blueish clear and even black) on the fasteners and pipes is a chromate and is put on the zinc or CAD to protect it. The color is not there to make it look pretty. The color is a chromate and its purpose is to protect the acid - vulnerable plated surface. The chromate, like the the plated surface, is a sacrificial coating. Both the chromate and the plate's job is to protect the base metal from corrosion.

The color of the yellow chromate is variable and has many factors. The base metal surface finish, the quality of the plate and the timing of the chromate dipping are all variables that are not easy to control. I do my own zinc plating and thus I am very familiar with the process and its irregularities.

As was mentioned, applying a clear coat to the chromated part will greatly extend the life of the color and the plating below. But, it does eliminate most of the yellow chromate "rainbow" and imparts a glossier than normal finish. So that is a decision to be made - durability versus originality. I am not going to get into that can of worms.     

[SEB]

Lee and Wallace!
Many thanks for the explanation. Unfortunately time destroys everything. I mean the oxidation process that doesn't sleep 

[Shvegel]

mbebrim,  I think I know what you are saying.  There are some parts that have a very grey color to them.  As you have shown the latches and linkages for the soft top compartment, the hood safety catch, The long fitting on the cable for the automatic transmission neutral safety switch and the spring clip for the tire jack in the trunk.  You have done an excellent job replicating the color.  Closer than any I have seen.  I have tried using a colored clearcoat but have not come that close.

The "rainbow" effect for anyone who does their own plating can be avoided by simply blowing tha parts dry with compressed air after rinsing rather than letting them drip dry. 

[SEB]

The "rainbow" effect for anyone who does their own plating can be avoided by simply blowing tha parts dry with compressed air after rinsing rather than letting them drip dry.

It makes sense. I was told it depends on the cleanliness of the bath. So may be both?