Two-color anodizing

A. Hi J. We appended your inquiry to a thread with beautiful pictures of parts processed per your needs, and at least some general hints how to do it :-)

Luck & Regards,

A. Hi Coby. There are pictures of some really beautiful 2-color anodizing on this thread, but there are several problems ...

First, I don't know if three colors is truly practical in very highly decorative anodizing such as is in the pictures.
Second, white anodizing is a problem just by itself; it's not impossible, but is a specialized rarity.
Third, you have to find someone to do it; and one of a kind artistry is very expensive :-)

Luck & Regards,

A. I think that you can use epoxy based cold enamel for jewelry. If you really want to use anodizing then special anodizing pastes can be used, but that's not simple and easy process. Hope it helps and good luck!c

A. Hi, Nate. What you want to do can be done. In fact, very exotic multicolor anodizing can be done -- visit the paint ball gun section of a store for examples. But sandblasting is not the way for most. Instead, maskants are usually used. Mask the area , and anodize and dye and seal the rest. Then remove the masking, do your pencil blasting, and anodize and dye and seal that area. It would be best to mask the original area when you anodize the blasted area, but it may not prove necessary.

Most people don't encourage sandblasting of aluminum because it's so soft, so you might consider chemical etching as an alternative way to get a matte area. Possibilities include caustic etch and ammonium bifluoride etch.

Regards,

Ted, I appreciate the prompt reply and the information. I will explore masking techniques and pencil blasting further in order to achieve what I am looking for.

Thanks again for your thoughts.

A. Practically it is almost impossible; however, it is theoretically possible. First the first anodize must be completely sealed but most job shops never completely seal anything after the first day because their seal is contaminated or they use a so-called low temp seal which never works even the first day. If you get by the first seal, then the next problem is how to prepare the surface, after machining, for the second anodizing. Use a cutting fluid that is water soluble and find a way to get it off without harming the first anodizing, probably with solvent cleaning and water rinsing. Then, the same day you did the machining. before it sets a hard weathered oxide, dip it briefly in a ferric sulphate based deox, experiment with the max time you can use without leaching the previous dye, anodize and dye, good luck with that. It can be done. People who do splash gun dyeing, keep it secret, but many secret processes are out there.

A. Hi Thomas. As the three examples show, people are doing two-color anodizing in production. I have no inside information on it, but my guess is they are doing it by anodizing the whole part, then selective masking and into the first dye tank and seal, then removing the masking and going into another dye tank and seal. A second masking step before the second dye might be required though.

If I ran an anodizing shop and had a regular customer who wanted two-color anodizing I would certainly take that opportunity to figure out how to do it rather than let my business seep away to bolder shops.

Regards,

A. Thomas

The Sugino chain ring appears to have been black anodized, machined, then red anodized where the machining was performed. Not too sure about the other two items.

Robert is correct that if the seal is less than perfect, you won't be pleased with the results. Typically, the lighter shade is applied after the darker, as lighter shade doesn't require the coating thickness of the darker, and the immersion time in the anodize bath is shortened.

Masking the first coat and re-anodizing is an option but in most cases not cost effective. I have seen Ted's suggestion used where the article is anodized completely then masked for dyeing, with mixed success.

A. Hi again. I'm not looking at actual parts, only photos (and with the large number of postings to deal with, not even looking closely at the photos). So if you can see machining transitions precisely at the color change lines, my revised theory is that they were anodized, dyed, and sealed all over, then masked completely all over with a dipped, brushed, or sprayed masking material rather than using a reusable mask. Then the masked component is machined (it may be necessary to remove the masking at a few points for accurate jigging). If any masking was removed for the jigging, those points could be easily repaired with a brushable maskant without any need for precision, then the part (with the existing masking everywhere but on the newly machined areas) goes to anodizing, dyeing in the second color and sealing.

Regards,

A. Hi again. Sorry for the delay in posting your question and my response. Yes, well sealed anodizing can be used as a maskant to prevent further dyeing, but there might be limits to its total effectiveness. The masking I was speaking of is simple elastomer dips and brushable stop-off solutions made for the purpose. Even dipped wax may be useable if you are not doing heated cleaning or sealing, and only warm dyes. Where it suits, plater's tape can be used; it's similar to black electricians's tape except usually heavier and in colors like green (whether the adhesive is actually different, I don't know).

In the meanwhile, the below response came in from Geoff Smith, who is relating some actual experience in a similar process, rather than just book knowledge :-)

Regards,

A. Hi Thomas

I don't know if this helps but it could be worth passing on to your anodiser

Back in the 1970s at Kodak we developed multi colour anodising.

Standard sulfuric anodise but do NOT seal
Dip in methyl cellulose solution (common wallpaper glue)
Dry. This fills the pores in the oxide layer but prevents it sealing.
Print an image in resist - we used photoresist but you could screen print or paint an image. Dye the first colour. We probably cold sealed at this stage. Remove the resist with suitable solvent. Dry. Repeat the process with resist now coating the dyed area and producing another image on the undyed part, etc. We were able to produce a full colour image, yellow, cyan and magenta with a black overprinter of near photographic quality. The main application of the process was for the label industry.
All our work was on flat sheet but possibly it could be adapted.
If you would like to go the machining route, I must disagree with Robert Probert. There is no need to use cutting fluid for the light cut needed. Use modern carbide or ceramic tools dry and with a slow feed rate.

Ted,

Thanks for the update on the masking; this will help as we experiment.

Geoff,

Wow! This was a really great response. I think this gives us enough with which to experiment. Thank you.

I want to give out a tremendous thank-you to everyone who has contributed in the thread. The responses have given us a good place from which to begin testing with some local finishers.

A. I would attack this differently. I would apply the darker anodize coating first. Then clear coat the entire unit with a good polyurethane. Machine the surfaces requiring the lighter anodize and then apply another coat of the clear coat as the final finish.

A. Hi Mark,
There's a thread going on this topic that you might find helpful:
https://www.finishing.com/583/16.shtml

I strongly recommend a liquid maskant that has fluorescent dye in it so when you trim/peel it off, you can stick it under blacklight to be 100% certain there's no residue, including fingerprint residue from maskant contaminated gloves, due to the obvious value and time commitment of each individual wheel.
Also, get ready to buy or build a pretty good sized UV curing box. And lastly, have the techs PRACTICE, PRACTICE, PRACTICE on similarly contoured scrap parts. Application of brush on maskant can be a frustrating art! It's gooey and sticky and gets absolutely EVERYWHERE. But when you get good at it, the results are totally worth the learning curve!

A. Hi Donald. You can probably use wax, but a maskant made for the purpose might be better because after that laser engraving you might need to re-clean or re-etch or seal at a temperature a bit high for wax.

Although myself and others with some anodizing and metal finishing experience may make some good guesses, you would probably be better off, if possible, sending your buckle to an anodizing shop with two-color experience rather than trying to advise a shop 3rd hand how to do something neither they, nor you, nor probably we responders, are experienced in :-)

Luck & Regards,

Thank you for the feedback. You are right. As long as it is possible I only need to find someone to do it. Perfect.
Thanks again.