Hi Guys,
Just a quick note regarding the “gold” looking plated parts from Mercedes-Benz engines and other parts of the 60’s. This was not actually a zinc coating at all but an electroplated cadmium coating. Cadmium is a soft white metal that is plated onto steel, and other ferrous materials. It protects the surface as a "sacrificial coating," corroding before the substrate material. Unfortunately cadmium (apart from being a little dangerous to health) is soft and can be easily deposited onto hands by repeated handling the article. To enhance the corrosion protection of cadmium plating and minimise health risks, plain cadmium, that has the potential to come into contact with the body, has a chromate conversion coating that can be applied over the plated metal, yielding the familiar gold colour as Henry has noted.
By the 80’s health and safety issues meant cadmium was being phased out in favour of a very thin coating of zinc. Zinc normally has a shiny surface but is often dull when the surface preparation is less than optimal, or it is being sacrificed to preserve the base metal. There are platers that can passivate this material too, in an attempt to give it the cadmium look, however, it does not enhance the protective qualities of the plated materials.
My 1951 170S has fasteners (nuts and bolts) protected by oil “blueing” of the steel parts, with no other protection applied that I can see. There is little or no plated parts in the whole vehicle other than the bright metal decorative parts. I suspect you’d need to get right up to the 1960’s before seeing passivated cadmium. By 1990’s this too was disappearing for zinc.
For accuracy, fasteners should have that familiar black “oil-blue” colour up until 1953 anyway.
