White powder (mold? galvanic current?) on chassis outside surfaces

[slidincharlie (Carlo P)]

Hello everybody.
I've been missing from this forum for a few years. Actually I haven't opened an amp in a long while.
Back I am with a little query.
The chassis outside surface in my SF Vibrolux Reverb - which I haven't used for a few years - is covered with a sort of greasy white powder. It's not just normal dust, it's more of a greasy powder that comes off with a vigorous rub.
It is on every exposed surface - chassis, filter caps hood, and tube shields.
It is not on other parts EXCEPT one single screw on a tube socket (see photo). Inside the chassis and beneath the filter caps hood the surface is clean and shiny.
My home, as everywhere in the city, is relatively humid (I giess 60-80%) all year round. Yet this is the first time, and the first amp, with this issue, and I've owned amps for about 30 years.
What could it be? Mold? Doesn't seem so really. Maybe the result of some sort of galvanic current?
Anything that I should be worried of?
Can I just wipe the powder off and use the amp as usual?

[Helmholtz]

That's not unusual. It often shows on zinc plated steel and is called white rust.

The white powder is mainly zinc hydroxide as a result of zinc corrosion.

https://www.corrosionpedia.com/does-zinc-rust/7/7030

You may try to rub it off with some WD-40 on a cloth.

Interestingly it doesn't seem to develop with BF amps, which used a different plating.

[slidincharlie (Carlo P)]

Thank you Helmholtz.
So it seems nothing I should worry about.

[Tom Phillips]

...So it seems nothing I should worry about.

At least you now know that it's not a unique problem with your particular amp. Fender changed their chassis finish in 1966 discontinuing the nice chrome plating that they previously used. On occasion I have used a good quality silicon based car polish to clean that white film off. The polish also sealed the surface and slowed the return of the white powder. However, that treatment takes a lot of detailed effort. It took 50 years for your chassis to develop the amount of white powder that your photos show so even a quick wipe down will improve the condition a lot.
Cheers,
Tom

[Chuck H]

I'd sticky this thread except that this issue isn't mentioned much (so it's wasted forum real estate). Still. it's exactly this sort of profoundly intimate knowledge of guitar amplification past and present that makes this forum and what it's membership brings so fantastic.

I believed I recognized it as zinc oxide because of my familiarity with it in different circumstances. But not being aware of the particulars with specific eras of Fender chassis and never having had this problem I wouldn't have posted because I couldn't be sure. It's just really great to have members like you guys (Helmholtz and Tom) that share valuable and deep experience.

[Chuck H]

And kudos to Charlie for good reporting and photographs. This can be the most important aspect of resolving a thread

[Helmholtz]

Fender changed their chassis finish in 1966 discontinuing the nice chrome plating that they previously used.

Are you sure it was chrome plating?

It looks smooth and yellowish (as opposed to the grey-white somewhat blueish zinc plating), not typical for chrome plating.
I thought it might have been cadmium plating also being the reason why is was discontinued.
In a former thread about this issue Mick Bailey suggested zinc plating with a special passivation treatment, though.

[Tom Phillips]

Are you sure it was chrome plating?...

The 1965 and earlier Fender chassis plating sure "looks" like chrome plating to me. Maybe it was nickle. It was hard, very shiny when new and it polishes up well during a restoration. A clue may be that one could solder directly to it. I have read that it is difficult (maybe not possible) to solder to chrome but is possible to solder to nickle. Back in the 60's and early 70's I would take steel chassis that I built to a local plating shop to have them plated. They would clean them, put on a copper flash coating and then the nice bright coating. Although I asked for "Chrome", the final product may have been something else. I could solder to them, they looked like the 1965 and earlier Fender chassis, and they never developed the white powder growth.

[Helmholtz]

The only chrome plated Fender chassis I'm sure of were with Tweed amps.
Nickel looks more yellowish than chrome and might be a possibility.
OTOH, cadmium plated hardware wasn't uncommon till the 60s.
I have some old cadmium plated screws that look exactly like my BF amp chassis'.

[slidincharlie (Carlo P)]

Thank you guys for advice and insight. Now I'll try to clean it.
WD40 as per Helmholtz's advice is oily (correct?) so at a first glance it doesn't seem a good solution. But I can try it on a corner.
As regards car polish, I guess I still have a small old can. Again, I will try it on a hidden corner.

[Helmholtz]

I recommended WD-40 because it loosens the white powder and is water repellant (that's what it was developped for).

If applied on a cloth (not sprayed) there won't be much oily residue (just enough to keep moisture off).

Using an abrasive polish though might remove more of the protective zinc layer than necessary.

Once there are voids in the zinc layer, the steel beneath will start to rust.

[Tom Phillips]

...I have some old cadmium plated screws that look exactly like my BF amp chassis'.

Interesting. I found the attached photo and accompanying web link. I still have two chassis I made in the 1960's which I may locate and inspect when I have time . I'll pay more attention to the plating on the chassis and hardware as items come through the shop. For now, suffice it to say that that the 1965 and earlier chassis had a nicer finish.
Cheers,
Tom



https://www.sansmachining.com/what-i...ickel-plating/

[mozz]

Be sure it's not cadmium.

[Helmholtz]

As said, cadmium plated hardware was quite common until the late 60s.

My old chemistry books from the early 60s don't even mention that cadmium is a hazardous substance.

[SoulFetish]

I thought it might have been cadmium plating also being the reason why is was discontinued.

Cadmium. mmmmm.... yum.