"Dull Cad" Gas Cap Finish? need some guidance

[Patrick N.]

I have plated my gas cap a couple times trying to achieve the "dull" cad look. I have reached the conclusion that I really do not know what I am shooting for as far as a final finish and could use some help.

What is the generally accepted finish that passes judging? Is it more of a range / subjective per judges?

Here is the Cap in my latest plating attempt... (Process: Acid dipped to remove old finish down to bare metal. Zinc plated, then mild acid dip to "dull" the brightness, then a quick final coat of zinc).

Thanks

[James G.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

To replicate CAD, I usually just plate with zinc but do not passivate it with the "blue"/bright dip, which leaves a more soft silvery finish.

100_2134.jpg

[Leif A.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

Patrick,
My original cap from my '67 restored by Peter Lindahl almost ten years ago. Starting to show it's age, but you can get a good look at the finish.

[Joseph W.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

I have a NOS gas cap I bought from David Sokoloski.
I can post up a pic if that would help.

[Ed S.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

Well James -- you made me do something my parents used to tell me to do....."look it up".. I read your brief comment and the word "passivate" got me.... What the hell is "passivate"? Had to research it - the internet is a wonderful thing. Now I know..... I bet a lot of others don't......thanks for the education. BTW - here is one of many links I found on passivation.... this one is pretty good. https://clintonaluminum.com/passivat...teel-aluminum/

[James G.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

Same exact thing happened to me... happy to pass it on
I have used the black passivation, the yellow(gold) and the blue, not tried any of the olive green, however it is supposed to have the best longevity.

Here is a link to a video I made Black Passivation of zinc screws for the eve vents on my house. I used the CASWELL PLATING solution.

https://youtu.be/6eKqE5Q9zWM?si=dRJ9QzR-Va--qNwq

[Ed S.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

Not exactly sure what you were doing in the video - but the finished product (treated fasteners) looked like you "parkerized: them. Can you explain what you were doing in the video..... and why? Thanks.

[James G.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

I just dipped them in the solution then used the heat gun to dry them off then sprayed with silicone.
That is the recommended procedure.

They are black zinc which is actually semi gloss unlike parkerizing which is a rougher finish.

[Ed S.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

Thanks - interesting. Parkerizing protective coating doesn't last all that long.

[James G.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

black zinc lasts quite a bit longer than silver zinc, eventually the black outer will fade away and the silver zinc will remain after that.
I have some pieces which when the screw was removed there was a black ring on the apparently silver zinc piece, and it has a shimmer, irridescent appearance, like the gold has tones in rolling light, the black does as well. Not very visible on bolts, however I will get a photo which represents how the finished color looks to the eye.

If you want to do the process to purchased bolts which are silver zinc, you have to wash them with whatever it takes to makes them pass a water break test.
Typically I use purple power then lacquer thinner, blow dry with clean air and into the solution.
If you are doing your own plating, well then your parts pass the water break test and you know the drill.

With the gold dichromate I made a stick which I plated about 7" long 2" wide plated like I was the parts, then into the gold for 10,sec pulled out washed, dunked 4" into 10 sec remove wash then dunk 2" for 10 sec then I had a grade stick to reference how GOLD it needed to be.

So I had top 2" 10 sec next 2" 20 sec final 2" 30 sec. more and more yellow gold darker. YEARS ago I did this.

[Ed S.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

So I gotta ask.... if you research a part number of a fastener on this forum or other sources, or read the description of the fastener in a judging guide, it usually says one of the following, natural, zinc, cadmium or black phosphorous ---- I have never seen the finish of any C2 part described as black zinc - there may be some but I have never seen a finish described as black zinc. So... what parts are you applying the black zinc finish to? Sounds like overkill to me - not that there is anything wrong with overkill. And, how do black zinc items do when judged?

[Patrick H.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

Not a C2, but I believe that the screws holding the taillights in place on 70-72 C3s are black zinc given the color and gloss level.

It's not a common finish in vintage cars.

[Patrick N.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

Thanks all for the replies! great information and pics! I am going to redo my plating today to get it a bit brighter than what I have. James and Leif, the pics are very helpful - I have a target to shoot for. FWIW, I have my system set at 9V and about 5amps when plating the Zinc. I have good results with the coverage and texture (I've had the power too high in the past and got a very granular texture).

I will post pics of the new result later. Many thanks again!

[Patrick N.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

thanks again everyone!

I replated the cap and am much happier with the results. I think they are more like the other examples and not so "dull" and gray-looking on the one I first posted. I don't think it matters, but i did keep the volts at 9 and lowered the amps to 2.5.
1968 Gas Cap SMC.jpg
Thanks!

[Patrick N.]

Re: "Dull Cad" Gas Cap Finish? need some guidance

...a slightly better photo of how the final result turned out.
20231115_171138.jpg