I should say that when I talk about them as being "yellow in colour", I don't mean that they are litteraly painted yellow. They are galvanized and where as zinc coating is usually a matt grey colour, these have a yellow/gold coloured tint, which has a slightly 'multi coloured' look to is (a bit like oil on water)
This is almost certainly the result of a zinc phosphate treatment. The color typically is yellowish, somewhat uneven, and you may see slight tints of other colors here and there.
It's unlikely you've run into cadmium-coated washers. Most hardware-store nuts, bolts, and washers are zinc phosphated or zinc chromated.
It's harmless to weld small quantities of zinc phosphate or chromate. However, you may find your washers have some significant amount of zinc metal on them. They could, in fact, be zinc-plated and then chromated, and, if you aren't sure what you're looking at, it could be the case. Welding zinc produces a white smoke that causes something called "fume fever." It's temporary, but the symptoms are almost exactly like the flu, and they're not pleasant. It doesn't take a lot of it to give you the fever. I speak from unpleasant experience about this.
If you want to avoid the chance, go buy a 3M "zinc fume" mask for around $8 at your welding supply shop. You don't want to weld plain *zinc* without a mask, and that's what the white smoke is.
Zinc phosphate coating are black, whether applied to zinc metal, or steel. Zinc phosphate coatings are typically there to aid in corrosion resistance, but also to aid in adherence of paint. Everything I've ever seen phosphated is painted soon afterwards.
Zinc phosphate is similar to manganese phosphate... except the manganese flavor is much more durable and corrosion resistant. I believe the military M16 rifles are parkerized, which I think is a Type-1 manganese phosphate coating. Oiling this coating is sufficient for good corrosion resistance.
Most fasteners are zinc metal coated, usually by plating rather than dipping. The gold color is a chromate coating on top of the zinc. (although the same color can be made by putting a chromate coating on cadmium)
Many military specs call for cadmium plating, with the chromate coating. I know of military manufacturing facility that purchased most of their fasteners from foreign sources because the cost of waste disposal of cadmium plating solutions was too much, and foreign sources could underbid the US suppliers. Each shipment was tested, and on occasion counterfeits were found. (zinc coated fasteners were shipped with documentations saying they were cadmium plated)
But most if not all hardware store fasteners are zinc plated.
Some manufacturers have done away with the gold colored chromate coating, and are using other coatings that don't contain the hazardous chromium chemicals. (local farm supply store here has blue and red bolts)
PS: I have brazed hot-dip galvanized pipe fittings, and gotten sick as heck. Since I had more to do, (and I wasn't aware of a fume mask) I tried the milk trick, and it worked for me. The problem is I usually forget about it until after I am sick. Drinking the milk beforehand is a great preventative measure.
Yeah, I should have stuck to the chromates (chemistry makes me stare off into space), but zinc phosphate is usually light gray, except for the "heavy" coatings which are dark gray. The black stuff usually is manganese phosphate or a manganese-zinc phosphate.
The conversion coatings used in high-volume consumer products, like hardware-store nuts and bolts, are typically more complex, proprietary chromate coatings on top of electroplated zinc, as you say. The very yellow ones are dichromates.
I wish the milk worked for me. If I drank any more I would have thrown up.
That was before I learned about the dangers of it, and about removing the zinc (it was EMT tubing) with hydrochloric acid first. It was somebody here who pointed it out to me.
-- Ed Huntress (remove "3" from email address for email reply)
The problem with grinding is knowing when you have removed the zinc. So as to get the zinc off but not ugly up the stock (washers). It's much easier, better, and faster to dissolve the zinc with muriatic (hydrochloric) acid. Typical electroplating on hardware is gone in seconds.
A quart of muriatic at Home Depot is a couple of bucks. Drop the washers in some, rinse _really_ well and immediately oil. The now super-clean washers will rust before you eyes otherwise. Do it outside (!) and don't breath the fumes.
I can assure you that they are not galvanized with cadmium. Galvanize is zinc period.
Depends. Most metal sulfides are white or black but cadmium sulfide is yellow (also arsenic sulfide).
Many years ago "street cars" were pulled by horses and the front of the white cars were yellow after a relatively short time in service. It turns out that the white paint contained a cadmium oxide (white) pigment. However the flatulence from the pullees contained various obnoxious smelling mercaptans which reacted with the cadmium oxide in the paint producing a yellow compound which was a cadmium mercaptan. The result was a bright yellow front and snowy white posterior.
Now if you have stored these items in an outhouse or a barn you may have a similar product.
In the paragraph above you said zinc phosphate coating are black. In this paragraph you say zinc phosphate is usually gray". Both wrong. It is white.
Manganese phosphate is probably pink but I digress with more chemistry than you ever wanted to know.
Probably, but who knows?
If your hair doesn't fall out and your balls don't shrink to the size of a couple peas you may have drunk enough milk but don't count on it. Sometimes you will find you have only lost perhaps half your hair but your balls have suffered the consequences and atrophied and fallen off. Most people don't make enough money playing this game to risk the consequences.
Is that what's on all those old things? I've got some pretty much untouched-for-45-years tweeters (the big 4" kind) that look slightly dusty yellow-green over the steel. I've heard of old radio chassis covered in the crap too...
-- In the immortal words of Ned Flanders: "No foot longs!" Website @
But we are talking about zinc phosphated steel, which is gray, the shade of which depends on the coating weight. The heavier the coating, the darker it is. (ed is right, it is probably 75% black at it's darkest)
However, zinc dichromated zinc metal is very black.
Nope, we are right. The color depends on the base metal to which the phosphate is applied.
Pure manganese phosphate is pink, True. But manganese phosphated steel is very black.
You are barking up the wrong tree if you want to talk about chemistry. Put your high school chem book away, and look in an industrial coatings book.
Not the conversion coatings you see on steel parts. The thin ones typically are light gray; the thick ones are dark gray. Not always, but usually.
Two different people said those things. The zinc phosphate conversion coating, if it isn't modified with something else, generally is a shade of gray.
I used to. Oakite was my client, and I wrote a lot about their conversion coatings. There was a time I could tell you which proprietary brand names produced what kinds of coatings. But my memory isn't what it used to be...
-- Ed Huntress (remove "3" from email address for email reply)