How long does it take to patina aluminum?

[aquaman67]

I stripped the coating off a Benchmade 720 aluminum scales (sacrilege I know) and an trying to get a patina before stone washing. (I used glass media in a baby sand blaster from Harbor Freight)

They've been soaking on 100% white distilled vinegar for 2 days now and they haven't darkened a bit. I even added some OxiClean thinking that might help. It just foamed up a bit.

How long is this going to take?

 

[aquaman67]

Ok,

Never mind.

After reading more on the internet I found that patina-ing aluminum depends entirely on the alloy.

So....instead of acid I went with alkaline.

I had some lye so I mixed about a tablespoon in a small plastic coffee can with hot water.

The reaction was immediate. It even took off the black coating inside the scales - which I didn't bead blast.

Then I used a large coffee can and some ceramic media to stonewash.

I'm pleased with the results and will add this knife to my rotation.

 

[Bill DeShivs]

Aluminum doesn't "patina."
The coating you stripped off was hard coat anodizing. Now you have exposed soft aluminum. This is not a real problem, except it will scratch easily and mark your hands and clothing.

 

[Obsessed with Edges]

Aluminum doesn't 'patina' to a dark oxide like steel does. It's oxide is basically white(ish) or very light grey in color, so I don't think you're going to get a similar effect as with oxidized steel. And vinegar may or may not do it anyway; a stronger chemical etch may be needed, if anything is going to do it at all.

Think of aluminum kitchen/cookware that's heavily used on the stovetop, or long-cleaned in automatic dishwashers (caustic detergent + water + heat), which leaves them with scaly white/grey stuff all over. That's what oxidized aluminum usually looks like.

And if you're planning on stonewashing the scales(?) anyway, after the fact, any oxide that's there now won't be, when the stonewashing is done. Not sure what the objective is, if that's what's being done...


David

 

[aquaman67]

Aluminum doesn't 'patina' to a dark oxide like steel does. It's oxide is basically white(ish) or very light grey in color, so I don't think you're going to get a similar effect as with oxidized steel. And vinegar may or may not do it anyway; a stronger chemical etch may be needed, if anything is going to do it at all.

Think of aluminum kitchen/cookware that's heavily used on the stovetop, or long-cleaned in automatic dishwashers (caustic detergent + water + heat), which leaves them with scaly white/grey stuff all over. That's what oxidized aluminum usually looks like.

And if you're planning on stonewashing the scales(?) anyway, after the fact, any oxide that's there now won't be, when the stonewashing is done. Not sure what the objective is, if that's what's being done...


David

Fair enough.

Patina isn't the right word. Oxidation is.

Bare aluminum will oxidize. Forcing the oxidation "ages" the aluminum quickly.

The reason I stripped the black coating off was twofold.

Firstly - the Butterfly logo was only on one side of the knife - the side I put the clip on. So the clip covered half of the logo and looked terrible.

Secondly - the black coating was going to get scuffed and scratched over time anyway. So I decided to kill two birds with one stone.

The reason to oxidize the scales was to darken them before stone washing them. The "scratches" the stone washing make are brighter and stand out against the oxidation. And yes, the scratches and oxidation will change over the years. I can't wait to see how my knife changes over the years.

I like the way it came out and am very pleased with the results.