I've been investigating various ways to protect polished aluminum from scratches & wear. I just realized that everyday household silverware is very shiny/polished AND somehow very well protected. Does anyone know how silverware is treated? Is it anodized?

I've been investigating various ways to protect polished aluminum from scratches & wear. I just realized that everyday household silverware is very shiny/polished AND somehow very well protected. Does anyone know how silverware is treated? Is it anodized?

Have a look very carefully at your 'silverware', if it is very shiny, resistant to scratches, and does not tarnish it is probably stainless steel. Silverware, true silverware that is, made out of silver does tarnish, goes black eventually.

The only metal that can be anodized to my knowledge is aluminum. Stainless steel can be 'passivated' by treatment with strong acid , and this is a bit similar to anodizing in that it creates a strong corrosion resistant film on the surface of the stainless steel just like anodizing creates a corrosion resistant film on the surface of aluminum.

Geof - thanks for the info. Yes, this is probably stainless steel (not real "silver").

I was hoping to discover a way to protect aluminum without diminishing the mirror-quality I have achieved with polish (other than anodizing). I thought "silverware" my be a good example of the result I'm looking for.

The only metal that can be anodized to my knowledge is aluminum.

Unfortunately, what is often called the "Anodization" of aluminum is actually not a true anodization, it is a different process entirely used to get a similar result, and so indeed is unique to aluminum. It confuses a lot of people that way. True anodization itself can actually be done to about any true metal (Aluminum isn't actually technically metal, hence the different process). I frequently anodize Titanium, for instance.

Stepper - when folks talk about the DIY techniques of anodizing as seen on sites like focuser.com and caswell.com - is that "true" anodizing?

...(Aluminum isn't actually technically metal, hence the different process)....

Well if you want to get technical anodizing is an electrochemical process in which the metal to be anodized is made the anode in a electrochemical cell. The current flow, in the presence of something that will act as a catalyst, and oxygen, drives the natural oxidation of the metal surface further than occurs simply due to reaction with atmospheric oxygen. This resuilts in a thicker than natural oxide layer on the surface of the metal, and in the case of aluminum this oxide layer tightly adheres, preventing further reaction except under unusual conditions, also the aluminum oxide layer is extremely harde and provides some protection against scratching. It is also clear and with the correct electrochemical bath conditions, highly polished aluminum can be anodized without losing the polish.

The passivating process on stainless steel is analogous to anodizing in that it is done in a strongly oxidizing acid bath and this creates an oxide layer on the surface of the stainless which also tightly adheres preventing further corrosion. Ordinary steels cannot be passivated because the oxide layer flakes off exposing fresh un-oxidized steel underneath which then oxidizes and flakes off; i.e. the steel rusts away.

It is news to me, and probably would be to all the metallurgists in the world that aluminum is not a metal. Do you really know what the chemical definition of a metal is?

It would also be news to anodizing companies that whatb they do to aluminum is not anodizing given that the term relies only on the direction of current flow in the electrochemical bath.

It is news to me, and probably would be to all the metallurgists in the world that aluminum is not a metal.

Aluminum is actually classified as a metal, although it has kind of a strange spot among metals and it doesn't actually meet all the requirements, hence its different behavior. It sort of straddles the line between metal and metalloid. By its position on the periodic table it should fall into the category of a metalloid, but still meets most but not all of the properties of any specific metal group (alkaline earth, transitional, etc.). It doesn't really cleanly fit anywhere among the normal metal categorizations, and so just gets lumped into the category "other metals" as there isn't anyplace else to cleanly put it. Point, it doesn't always fully act like a metal.
The details are all actually pretty irrelevant to the discussion at hand, as long as you remember that there are a few elements we normally think of as metal in day to day usage that aren't quite fully there in one way or another, and hence on occasion can react in rather unique and unexpected ways when it comes to some processes.

When it comes to the process of anodization, it is done in a somewhat different way on aluminum than other metals. The processes indeed all designed to build stable oxide formations on the surfaces of the metal, and all use the target piece as an anode. There the commonalities end, they aren't nearly the same processes, limitations, or the same results. They are similar and both commonly called the same thing, and hence the confusion.

The fact is that anodization can happen to more than just aluminum, though to be clear aluminum anodization is a somewhat different ballgame than with other metals in fundamental ways and so the process differs. I simplified for clarity. That or I'm just plain ignorant, as someone whose sole job it is to habitually point that in all others not matching his illustrious smug brilliance has so kindly suggested.

I could go on forever constantly refining and justifying these statements ad nauseam in mind-numbing detail, but this isn't my thesis paper, and this isn't really the place to argue electronegativity, atomic radii, or oxidation states, nor do I feel like feeding the troll. There is a different kind of negativity involved here.

The fact remains that the answer the question posed is that yes, you can anodize more than just aluminum, it just doesn't have the same limitations as with aluminum.

Oh dear, have I annoyed Stepper Monkey: Again? :D

If you just needed corrosion resistance, you could alodine aluminum--even at home. It's what they do to aircraft parts. I don't think it would offer any measurable scratch protection.

For a nice shiny finish on aluminium you could try electroless nickel plate.

And I believe you can now get electroless chrome plating kits too.

Nick

Yep, electroless nickel plating will give you a durable high polish finish.

Has anyone had a experience with the stuff that could give some recommendations on electroless nickel?
I know it is very useful stuff and many people swear by it. That being said, I have heard as many people swear by it as swear at it. I think mainly problems with peeling/flaking. I will assume (just a random guess) this likely just has a lot to do with improper application and/or surface preparation, as a lot of people have said it is really very easy and have had great success with it.
What is the cause of the difference in result? Anybody know?

Yep, electroless nickel plating will give you a durable high polish finish.

On aluminum?

It was years ago, but I wanted some aluminum nickel plated and it had to be done electrically. I was told electroless would not stick, and even bath plating needed some surface pretreatment and was not guaranteed to be durable. I was told the oxide layer on the aluminum is passive and will not form a metallic bond with the plating.

If I remember correctly you need to use strong acids then strong bases then water and so on. I think you can electroless nickel plastic or just about anything. No electricity involved. A plater company would know better than myself.

The sub contractor I used for anodising, electroless nickel plating and anodising/ passivation etc went out of business cos of all the new regulations concerning chemical safety and stuff. I think it was the alchromating regulations that was the final nail in the coffin so I can't even ask them.

Hey! perhaps you could sub- con it to China, they don't care about health and safety. Send em a few samples and see how they go!

http://www.electroless-nickel-plating.co.uk/about.html

Wiki is wrong on this process btw, they only cite one process, I think there are about 3 at least.

The oxide layer on aluminium wasn't really a problem for me since I only dealt with polished or DM'd stuff, but it is a good point Geof.

from the home anodizing set up I use I can get good results, here are a few examples. The surface is a little more scratch resistant and the shine is only as bright as the part was before it gets anodized.

Keep in mind though that the scratch resistant qualities are not great in a home anodizing set up, it provides some resistance but not much. Sorry no actually hardness test or scratch test to back this up, just from what I have done.

I have also tried to anodize titanium but have never got the system down to produce any consistant results...

Courtesy of Google.


http://www.pfonline.com/articles/079906.html

from the home anodizing set up I use I can get good results, here are a few examples. The surface is a little more scratch resistant and the shine is only as bright as the part was before it gets anodized.

Keep in mind though that the scratch resistant qualities are not great in a home anodizing set up, it provides some resistance but not much. Sorry no actually hardness test or scratch test to back this up, just from what I have done.

I have also tried to anodize titanium but have never got the system down to produce any consistant results...

The coating toughness depends alot on how well the bath temperature is controlled during the run. Keep it at 68-70 all the way thru and the coating will be harder then if you ran them at 72-74. Of course a harder coating is going to take to dyeing less then a softer more porous coating.