Cadmium versus Zinc Plating

[Joe L.]

Very often when I hear hobbyists talking about cadmium or zinc plating, it is apparent that there exists some misunderstanding regarding the difference between the two types of finishes. For some reason, many folks seem to think that plating which evidences a "goldish" color is cadmium, while plating finishes that are "silvery" are zinc. That is not the case. Both cadmium AND zinc plating produce a silver-like color. There are subtle differences in this color, with cadmium being a "brighter" silver and zinc often evidencing a VERY slight "bluish" tint. However, for all practical purposes, they are basically indistinguisable. Cadmium is more durable, though, and that is why it is called for in many military specifications.

The "goldish" color which some folks think is cadmium is actually the result of a "bright dip" which is a plating operation that can follow either cadmium or zinc plating. This "bright dip" is actually a "chromate" coating applied to improve the durability and appearance of the plated part.

[P. Terry #6573]

Re: Cadmium versus Zinc Plating

I find that there is more of a difference between cadmium and zinc than you mentioned. Typically, cadmium finishes appear to be a silvery dull type finish, where zinc is silvery, but has much more gloss to it.

[Jim J.]

Re: Cadmium versus Zinc Plating

Hi Joe, I hear of people often confusing the heavy metals that you have identified. Let me just tell you what I know. Zinc was the most widely used plating in the manufacturing process. It was often dyed different colors, yellow or even black, but most commonly came as clear zinc.. Over time, clear or yellow zinc fades leaving a dull finish that "resembles" cadmium. Irridite, is a trademark name for zinc and is often used a term to describe zinc plating. Cadmium, due to it's high level of toxicity, was indeed rarely used. From what I have seen on "original" cars, it apppears that it's use was phased out in the fifties. I mentioned toxicity. You do not want to handle cadmium. It is right up there, possibly even more dangerous than lead. So if you choose plating materials. I suggest zinc. It is the correct finish for most applications and does not pose the health risks. Jim Jordan

[Chester]

Re: Dust shields then?

i have a 68 with a body build date "I" for April, what's the finish on the front and rear brake dust shields? Front Caliper mounting brackets? The "Manual pg 94" says the are to be Unpolished Zinc--Dust shields and dull gold iridite--caliper mount brackets The front shields I ordered were "silvery 'zinc" colored and the rears were the goldish color.--I'm assuming the rears are wrong,correct. Paragons got a pair of "Zinc" Rears assuming they are not the goldish color. What was the general finish of most of the bolts, not including the ones "blacked out?"--Zinc?

[Gene M.]

Re: Dust shields then?

Only as a general rule on backing plates the mid yrs used a silver cad (replicated by zinc with clear chromate) finish, while 68-72 used the cad dichromate (replicated by zinc with a yellow chromate treatment) that gives the gold appearance. Back in the sixties the plating of choice for screws and bolts was cad, black oxide, phosphate, some zinc. The prefered from corrosion stand point was cad. The color differences of clear, gold and black were done with dyes in the chromate treatments. Most but not all fine thread bolts were black oxide or black phosphate. Replication using zinc with black chromate will give far better rust protection.

[Joe L.]

Re: Dust shields then?

On my 69, the original front brake shields were zinc with chromate "bright dip". The rears were made of "pre-punch" galvanized material. In this type of construction, a blank for the shield is produced in a punch press from galvanized sheet metal. Then the shield is stamped out using appropriate dies. This yields a finished product and no further plating operations are performed.

I am absolutely certain that this was the manufacturing method used for production of my rear shields. A very experienced plater examined them and identified this type of finish. Since he's an individual that I have known for 20 years or so, he pointed out to me all the fine nuances of identification of this type of construction.

I am also certain that these shields are original. I have owned the car since new and no one else has EVER worked on the rear trailing arms. Also, the shields contain the Delco Moraine logo. Of course, I guess someone could have slipped into my garage one night and changed them without my knowledge. I don't think so, though.

[Terry M.]

Re: Dust shields then?

Chester,

Regarding the color of the dust shields on your 1968 - I expect the 1968-1969 Technecial Information Manual & Judging Guide would say the same as the 1970-1972 version which states the front & rear dust shields should be silver color. I think Joe is giving you good information re the plated finishes.

Terry

[William C.]

Re: Dust shields then?

Just as a note regarding the discontinuance of general use of Cadmium in GM, I worked in an area where Cad was plated (GM Division) and it wasn't until the mid-70's era that Cad was replaced, usually with tin, as Zinc was a relatively poor corrosion protection medium. That was internal use. Sources outside GM may have continued to supply Cad plated parts after that time (Bolts & such). The discussion with regard to the gold wash is correct in that it was available on both Cad and Zinc plated parts. There are differences both in appearance and in the way corrosion protection is achieved. The irridite finish (gold) was used when added corrosion protection was desired.

[John]

Re: Cadmium versus Zinc Plating

The OEM automotive industry has eliminated use of cadmium-plated fasteners and small parts handled in assembly plants, as cadmium has been identified as a carcinogen.

[Jack H.]

Re: Cadmium versus Zinc Plating

Are you certain it's been proven cancer causing? Basic chemistry tells us it's a poison (just like those elements adjacent in the periodic table -- tin, Etc.) but I'm not so sure poison = cancer....

[Pete Lindahl]

Re: Cadmium versus Zinc Plating

While I believe that cadmium is classed as a carcingen and yes, it's toxic, etc. and I would certainly not recommend that we go out and lick or eat the Cd plated parts on our cars, if there are any. I suggest that the reason most parts aren't Cd plated is because of cost. While Cd plating is more durable, Cd metal is more expensive than zinc so most of the original parts many of us think of as having Cd plating were most likely Zn plated.

[John]

Re: Cadmium versus Zinc Plating

Jack -

OSHA and EPA have classified cadmium as a carcinogen, and have begun to regulate it as such over the last 24 months. Whether it really is is still open to professional medical debate, but that means nothing once the regulations are published. Have you noticed how many (smaller) plating shops have simply disappeared in the last two years? There's a reason..........

John