Brush anodizing / Anodizing Pen for Touch-ups

A. Hi Bob. No picture was received ... please e-mail it to mooney@finishing.com for posting here.

I think it's possible to do either of those or several other techniques. Two color anodizing is explained in thread 48706 and there are several pictures of beautiful work there. Hand painting is explained and illustrated in thread 60640. There is also "splash anodizing" which you can search for on our site; it was very popular for paint ball guns so I'm sure Google has lots of pictures.

As a matter of semantics when you look for supplies though, if you are trying to hand paint or silk screen you use "anodizing inks"; these are much more saturated than the "dyes" used for immersion.

Unfortunately I think you're going to find that doing this well is a protracted learning experience and much harder than most people would think :-)

"THE" brush plating book:
Electrochemical Metallizing by Marv Rubinstein

on AbeBooks

or eBay or

Amazon

(affil links)

A. Hi Robin. I find it distressing that many anodizing shops that I've visited keep black Magic Markers on hand for touchups of rack marks, etc. I'm sure that some of their customers permit this with full knowledge. But I'd bet that many customers have no idea that it happens, or are far enough removed that they have given permission without any real understanding of what they've assented to.

"Brush anodizing" would be an alternative, but perhaps prohibitively priced and not decorative enough. This "anodizing pen" is probably another term for a brush anodizing kit.

A. You would have to be a lot better than I am to ever get an acceptable touch up from dyed type 2 with brush anodizing. It is excellent for some local applications, but it is nearly impossible to satisfactorily use it for critical cosmetic touch up on a commercial basis.

  I'm sure you're right, Jim. I've never tried it myself, and the application here is on an R5 bright dipped part, which probably has to be perfection.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi Chris. We can't suggest vendors except our supporting advertisers (huh? why?), but I don't think the term "anodizing pen" is as widely used as other terms. Try googling "brush anodizing" and you'll find suppliers. Good luck.

A. It depends on what specs, if any, you have to meet. And it depends on what wear resistance you need in the repaired area. But, believe it or not, some people accept touching up with a black indelible marker.

A. Theoretically YES, practically NO. You will have to clean off, probably mechanically, all residual anodic oxide, make contact, deox briefly in Nitric Acid (some proprietary deox will work, others will attack the other anodized and dyed areas), put back in the anodizing tank and set the voltage for the alloy, redip in dye, seal in plain hot water.

I have done it, it is difficult.

A. A possible solution may be to brush anodize the bare spots. Connect the positive wire to the work, the negative wire to a cathode wrapped in felt,(ensuring the usual electrical safety issues are addressed)then wet felt with electrolyte, and brush over the bare spots. You must take into account the thickness of the felt, due to the possibility of arcing. This method is used to colourfully anodize titanium, so maybe it could be of some use to you.

Apparently a well bristled chip brush will hold a nice little piece of cathode up inside the centre of the bristles, using the power lead as a fastener. Trim bristles to appropriate length, allowing a decent gap.

Good luck!

A. Hi Marvin. There is no simple in-situ repair because anodizing is a factory applied electrochemical process that requires many steps: preparation, creation of the porous anodized film, dyeing, sealing of the film to keep the dye in and dirt out, etc. It might be well worth it to cover these thresholds with plastic or tape until everything else is done because repair is so difficult.

However, three thoughts...
First, it might be possible to have a skilled brush plater do brush anodizing on site, but this is more for functional purposes than decorative color matching.
Second, it is not uncommon for anodizing shops to use magic markers to cover very small spots called rack marks; it is possible that a brass colored magic marker could be found that would do a "passable" job.
Third, an approach that is a bit better than a magic marker is a chromate conversion coating of the discolored area. Suppliers of metal finishing chemicals offer "Iridite Pens" or "Alodine Pens" (Iridite and Alodine are brand names of chromate conversion chemicals), which might be reasonably close to the brass color and which would afford some measure of corrosion protection to the aluminum.

Good luck.

"Anodize look" paint

on eBay or

Amazon

(affil links)

A. Hello,

Some paint companies make coatings that match anodized finishes. If you have quite a few window frames to do and the marker doesn't cut it, you might want to look into a sprayed finish.

"The Surface
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby

(note: this book is two volumes)

on eBay or

AbeBooks

or Amazon

(affil links)

A. Generally speaking, you may rework only one portion, and mask the part with platers or electricians plastic tape, and brush/mop chem film the surface. Problems are the possibility of breaking portions of the anodize where you apply clamps and you will probably have a chipped edge where it is removed. Also, the quality of the chem film will probably not be as good as a regular tank application as it is somewhat harder to get a uniform cleaning/etch of the aluminum.

A. It seems like a simple "brush Alodine" repair, especially if corrosion resistance is not driving the design. Alodine (or chemical conversion) can be readily brushed or swabbed on.

A. 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 Gold Touch [a finishing.com supporting advertiser] or Sifco, and also to realize that some skill at the process is vital so you may need a lot of practice.

"THE" brush plating book:
Electrochemical Metallizing by Marv Rubinstein

on AbeBooks

or eBay or

Amazon

(affil links)

A. 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.

A. re: "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.

A. 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.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

A. 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 guidelines. If you choose to do it yourself, do a lot of researching and please be careful.

Jason Aube
- Flint, Michigan

Thanks for the warnings, Trevor and Jason!

Public forums are akin to "Hints from Heloise" or "Advice to the Lovelorn" columns in newspapers: while the response is labeled as being directed to one specific person, it's actually read by, and potentially used by, thousands of readers, from third-graders and post-docturals in advanced research labs. So we don't want to censor out answers which may be just exactly what a sophisticated & well-equipped reader is looking for, but we do need to warn people that just because an approach is technically doable does not means it's safe or should be done casually.

Luck & Regards,


Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Emma,

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.

Regards,