The finishing.com Hotline: Serious Education ... plus the most fun you can have in metal finishing. Ted Mooney, Webmaster
Anodizing with a paint brush++++
I want to know if there is any possible way of anodizing separate areas of a large sheet of aluminium without having to fully immerse it in a tank? Can I brush the solutions on and rinse them off out side with a hose pipe? If you leave the anodizing solution on longer will it have the same effect as it would if heated?Emma Boulding
Artist - Leeds, Yorkshire, England
It isn't clear to me from your letter whether you realize that anodizing is an electrolytic process rather than a chemical treatment, Emma. It is, however, possible to "brush anodize" aluminum. The "brush" in this case is not a typical paintbrush, but a gauze covered electrode. Anodizing is done at ambient temperature or below, so there is no need to heat the solution. You need to talk to a supplier like LDC [a finishing.com supporting advertiser], or Sifco, and also to realize that some skill at the process is vital so you may need to practice.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Brush plating is a misnomer. It is actually the electrodeposition of a metal by applying a current through an electrolyte whilst rubbing the workpiece with a saturated pad (also called a tampon) that has the electrolyte being pumped through it. The technique is also known as "selective plating" or "tampon plating". Anodising is not the same as electroplating as instead of reducing metal ions to a metal, you are oxidising a metal (aluminium) to aluminium oxide. However, in theory it should be possible to anodise aluminium, but one of the important things about anodising is to keep the temperature low; this is not very easy to do in brush plating. The best company in the UK for this is Selectrons, although they MAY now be known as Sifco; either way, they are based in Redditch, West Midlands.Trevor Crichton
"THE" brush plating book:
"I want to know if there is any possible way of anodizing separate areas of a large sheet of aluminium without having to fully immerse it in a tank?"
Disregarding brush anodizing for a moment and pretending your sheet of aluminum is laid horizontally like a tabletop...you can mask off the area you want anodized, place a tube slightly larger than the area you want anodized over top of it (picture a glass with no bottom sitting on your tabletop over the area to be anodized)and have some kind of seal (silicon caulk) at the bottom of the tube..fill tube with electrolyte and commence bath anodizing in tube container. now you can selectively anodize portions of large sheets with no huge bath but still get the ease of uniformity. you could also use this process on a vertical sheet with more difficulty.Jason Aube
- Flint, Michigan
Jason, yes it can be done, but you need to know what you are doing and what you are handling. It is not something that should be done in the home because the chemicals are very hazardous.
R&D practical scientist
Chesham, Bucks, UK
Yes that is true Trevor. I get caught up in the "could" aspect of questions and tend to forget the "should" aspects. Emma, as with many of the processes discussed on this site there are health risks involved. anodizing involves a risk of serious shock, hazardous chemicals, dangerous fumes, strong acids, etc. not to mention the strict environmental guidwlines. If you choose to do it yourself do a lot of researching and please be careful.Jason Aube
- Flint, Michigan
HI, there are definitely artistically viable ways of treating aluminium films to accept dyes as I have some prints using this method that only cost a fiver. Why exactly do you want to anodise the aluminium? If it is to accept a dye then there could well be an etch type treatment that could be applied as a wet chemical without needing the expensive hazardous electrochemical aspects of true anodising.
Also worth considering would be anodising the whole sheet and removing the anodising with a phosphoric/chromic acid mix. This might enable you to purchase a sheet already anodised and work backwards. Laser etching might be a good thing to look up all my mountain bike bits have logo's laser etched on.
- Leeds, England, UK