Aluminium black

Hi all,

Now that I have finished rebuilding my mill I decide to try it out making some aluminium dice. Two were milled at around 56mm square and I decided to get some aluminium black to colour the dots. So the surfaces were degreased cleaned and wiped down with isopropanol and let to dry. Applied the aluminium black with a small paint brush and made sure all of the dots were covered, waited a couple of minutes, bottle says wait one minute, then rinsed everything down. Finish results were very poor. Some parts black and others without any colour at all. The bottom of the dots seemed to be better where the liquid had pooled so should I have filled the dots completely and do one side at a time instead of trying to complete all sides at once? Is one or two minutes really long enough time? Any ideas?

Ian, many of these chemicals will give varying results dependant upon the composition of the aluminium alloy , however, whatever the alloy, it is important that at all stages of cleaning and preparation the item is not handled with bare hands no matter how clean they might appear to be, fresh rubber/pvc/nitrile gloves are essential. Perhaps on some dots the liquid formed a bubble across the top of the depression leaving the base clear?

It's proably meant to be immersed in the solution? There might not be enough activity even in a hole-filling droplet to get a good colour.

Neil

I've not used Aluminium Black but had trouble with similar products:

1. Stuff intended to repair an existing scratched surface often applies a temporary rather than a permanent coat. It's OK for covering up minor damage, but less satisfactory when you want a durable finish over a large area.
2. Domestic metal stains tend not to work well in my experience. Industrial processes for colouring metal involve heat, electricity and/or "exciting" chemicals.
3. Achieving absolute cleanliness with satisfactory removal of the oxide layer is hard to do. The symptoms of poor preparation are a mix of good and poor finish on the same job, so this could be your problem. Go ballistic on it! Give the items an ordinarily careful clean first. Then wearing new rubber gloves wash the dice is very hot water with a dab of detergent and a clean lint-free cloth. Dry the dice by rinsing generously in clean Methylated Spirits. Then scrape the dots with a clean tool to remove oxide, wipe quickly with isopropyl and dry with a clean cloth before immediately applying plenty of blacking agent. Do this as fast as you can. Leave the blacking to soak for a good few minutes, sacrifice a virgin, and test. On Aluminium the oxide layer starts reforming immediately - it may be necessary to do the sides one at a time.

Please report back - it's always good to know what works and what doesn't!

Dave

It it possible that it is designed to be used on anodised aluminium as the anodised surface can be dyed.

Les.

Edited By Les Jones 1 on 10/02/2019 18:14:52

Thanks for the input guys. I will have another go later in the week when I get a chance to get back into the workshop. I think I will try a bit scotchbright pad on the dots and then fill with the Ali black and leave for 5 minutes and see what happens but I will test on a bit of scrap first. Maybe differing grades of Ali need longer for it to work properly.

Good point.

Anodising dye won't touch a sealed anodised surface or a raw machined one.

If I was tackling this project I might anodise the die, colour it black, fill the dots with wax, strip the uncovered anodising and re-anodise, then seal. Alternative, anodise the blank dice and colour black, then add dots.

My experience with aluminium is that the surface oxidises really quickly, just minutes. If its a chemical reaction that is taking place then you need the aluminium to be "raw" You could try something like caustic soda to eat away the top layer and then try the blacking solution immediately after.

Chemicals like Birchwood Casey Aluminium Black work fine on material that's been exposed to air for weeks as long as it's well cleaned and degreased, keeping the surface to be treated covered with adequate fresh solution is essential, wiping it on and leaving it is a recipe for patchy results, different alloys take colour differently.

I tried to post last night but it seems it did not go in, as an engraver for some years I filled such items with cellulose black paint. clean/wash parts in thinner and then using a pegwood point drip paint into mark or engraving and leave to harden.

Clive

Has anybody tried UV hardening nail varnish for this kind of application?

Brian

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Not yet, Brian ... but it sounds like a very good idea

MichaelG.

I'll have to persuade my wife that she wants a UV lamp Michael...I have been working on her as it would be handy for photo etching

Brian

Managed to get a short time in the shop tonight and had another go. Cleaned the part down again and gave it a rub with scotchbright and cleaned again with isopropanol. Dropped several drops of Ali black into the spots with a small syringe and left for 4 to 5 minutes then washed down with water.

The results are far more promising.