Anodised Aluminium-query

[Ian Stewart-Koster]

I managed to pick up a tub full of round keyring or dog-tag blanks, as well as rectangular plaque shapes.
They're black, blue, red & gold.
I was told they were laserable.

I've been experimenting, and the blue lasers beautifully, cleanly and with good contrast. The red & black a bit less so, but OK.
Doubling the power, or halving the speed in engraving made not much difference.

But I can scarcely get a mark on the brassy looking gold one, when i was told it WAS laserable. (Maybe it's too reflective?)
I'm not really bothered, but I figured I'd ask here if anyone has a secret to getting an impression on anodised gold/brass on aluminium plaques?

I'm using our 50w ULS laser.


Thanks!

[Gary Hair]

Most anodized aluminum marks better with lower power than higher. If your marks are dingy looking or have a burnt look to them then you are using too much power or too little speed. Try running a power grid like you would for Cermark, starting with 1,000 dpi, 75% speed and 5% power and increase in increments of 5%.

[Ian Stewart-Koster]

Thanks Gary. I am happy with the red, black, and especially the blue results - I was just curoius if there was a solution to the reflective gold being lasered, at all.

[Kev Williams]

My simple answer is, the gold ones man not be anodized, could be a plating of some sort, similar to cheap 'brass' over aluminum trophy material. Other than certain 'custom' black anodized recipes that will barely lighten up at all, I've never had trouble lasering any other color of anodized aluminum. Lasering anodizing is a simple matter of 'bleaching' out the color of the dye used, so it could be they are anodized but the gold dye used is resistant to lasering...

Anodized surfaces are transformed into aluminum oxide, which is used to make sandpaper and grinding wheels, it's very hard; try scratch-testing the parts, a sharp edge of car key is a good test, they can leave a mark on anodizing that scotchbrite will usually remove with little or no trace. A straight pin can scratch anodizing, how much depends on how hard you try and the thickness of the oxide layer, if the gold scratches easier than the other colors then it's likely not anodized...

[Bert McMahan]

It is also important to remember that typically when lasering anodized aluminum you are ablating away the dye, not the anno layer itself. This is why lots of silver anodized tags don't laser well- it's because they are not dyed at all.

Different grades of aluminum will turn different colors when anodized and before they're dyed. 6061, for example, will stay mostly the same silver looking color, though perhaps a little darker. 7075 may turn a somewhat tan color. Without seeing pics, your brass color might just be the raw anno layer turning somewhat bronze. If it's a really rich deep color it's probably a dye or coating, but if its a more gentle tone it may just be a non-dyed anno layer. 2000 series is known for turning yellowish when anodized.

[Tim Bateson]

I think "ablating" may be a strong term. Some may take that as removal & yes I've seen a lot of bad anodized engraving where they laser down to the bare aluminum. I use the aforementioned "bleaching". As there is no removal of material, just a bleaching of the dyes.

As to the issues Ian is having, I agree with Kev - the reflective gold is likely not anodized.

[Bert McMahan]

Sorry if I was misleading, I meant it was removing the dye from the pores. I assumed it was evaporating/removing the dye from within the pores, though bleaching it is certainly possible as well. I would have guessed it's removing the dye but I really don't know.

[Ian Stewart-Koster]

Thanks everyone. I appreciate the feedback.

[Mike Thornbury]

The accumulated knowledge in this thread alone is awe-inspiring

That's why I love this site.