Mirror finish spray chrome paint: topcoat yellowing

A. Hi Jan. Although the topcoat naturally needs UV-inhibitors to resist yellowing, I suspect that some topcoats turn the silver nitrate layer below them yellowish.

Normally you buy the base coat, silvering layer, topcoat, and any required wetting/activation chemistry from a single vendor.

Luck & Regards,


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

A. Hi Zarron.

The first thing that probably needs to be acknowledged is that spray paint, no matter how high tech, isn't chrome plating. Don't expect to be happy with it on a truck bumper  🙂

There are some stories of success (I've seen Jay Leno videos on youtube), but yes, lots of cases of people abandoning it. It will probably be less expensive to farm out that coating service the first couple of times, so you learn what you and your customers find, before investing in it.

Luck & Regards,


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

? What does the paint supplier/manufacturer/franchiser (or whoever the principal is) have to say about it?

A. Hello,

I've seen the exact problem that you are describing. I have a feeling that there is a considerable amount of moisture still present after you have finished the silver nitrating process. The moisture is what is causing the brown tarnish, and it really doesn't matter if you are topcoating, as this traps the moisture (oxidation could occur quicker).

Try to run the parts past some kind of heat source, try 150-200 °F for 15 minutes before applying the topcoat.

Check with the manufacturer first to see if they might know what your problem is.

Sincerely,

A. Hi Adrian from Down Under,

I totally agree with Jake about your problems. However, it appears that you are not paying enough attention to details or instructions. Please be aware about the importance of strictly following the instructions.

One of the points as I recall was to make sure that the basecoat is baked for at least 1.5 hours in 130 °F and then the object should be left to cool down preferably over night. The chemical reaction and bonding with the basecoat will not take place unless you make sure that the basecoat is absolutely 100% dry. If your basecoat is not dry enough or the object is still warm, then the chemical reaction and bonding with your basecoat will not happen, even if the activator sheets, you will definitely have a milkiness in the "chrome" layer.

Then there is of course the obvious problem with UV, Sunlight and the effect on Silver nitrate (the "Chrome" layer). You need to block or shade the windows of your spray booth from sunlight, and changing your fluorescent lights inside the booth from "blue" UV emitting ones to a softer "white" light. You should know the effects this UV contamination can have in the "Chrome" layer.

Then there is another problem with not doing a thorough enough job blow drying your "Chromed" object. I have seen and heard of too many "painters" from the old school having this problem. Spend a few more minutes thoroughly blow drying the object you spent so many hours to prepare. Unfortunately, your eyes cannot pick up the trapped moisture under the "Chrome" layer. If you then spray the topcoat onto a moist surface, you should know the result. If you don't, here is what happens: Milkiness in your topcoat. There is also another reason why you could get the "Browning Effect". When you mix your activator, the TIN (II) chloride is very sensitive to: O2, CO2 and moisture. If you are not using all of the contents of one container and are using portions at a time, you MUST make sure that you do not use any metallic objects for measurement, close the lid immediately after use, only open and mix in a very clean environment away from any potential contaminants, and make sure that the container is never opened in a moist environment.

Be happy that by trapping moisture between the 2 layers of 2-pack, you did not get a peel off of the "Chrome" and topcoat. When you have trapped moisture in between the 2 layers and heat it up, think about what happens with the moisture. It tries to evaporate and becomes a gas (steam in this case). The result is the separation of the "Chrome" and topcoat layers from the basecoat (quite logical really). 99.9% of the problems lie with the operator and not the product.

Ed. note: Wow, Mike! Thank for such detailed and explicit advice!

A. You need to use black or silver basecoat to stop the streaky milking effect you are talking about,

Humidity must be 50%, temperature must be 25 °C to spray chrome,

Need to be put in a drying area far away from paint machine, (this is where your rust spots come from)!

Drying room should run cool for first 25 minutes to let the water dissipate, then you heat the room to 130 degrees for the normal amount of time

Clear coat should not be done until at least 24 hours after laying down the chrome

Basecoat must be polyurethane (helps with bonding).

Ed. note: Thanks Jason.

A. Response for Adrian Ridgway,

The browning after a couple of weeks may be also have to do with the handling of the product before topcoating. It is imperative you wear gloves prior to top coat, otherwise delayed contamination will occur such as the browning. Hope it might help a bit.

A. Maybe I am wrong, but your process seems to be a silver mirror technique; if so, you should control the contact time of your dual nozzle, distance, and time between coatings. Wish you good luck and happy new year.

A. Hi, Manny. When someone mentions a two-part spray gun, they are probably talking about what is known as "two-part silvering". Silver nitrate is sprayed from one nozzle, and a reducing agent from the other. This technology has also been used for silvering of mirrors, for putting a conductive coating on phonograph and CD masters in preparation for electroforming stampers, etc. I think you can learn more by googling "brashear process" or "two-part silvering".

"Standards and Guidelines for Electroplated Plastics"
by American Society for Electroplated Plastics

on AbeBooks

or eBay or

Amazon

(affil links)

But in trying to adapt two-part silvering for use as a chrome-look paint, it's probably worth working with the manufacturer and other users to try to solve these problems, as starting to do the research yourself from scratch will surely leave you many years behind the point that proprietary technology has advanced them to.

Real copper-nickel-chrome plating, especially on plastic, would be a huge step up from chrome-look paint -- nearly every shiny grille on every new car in the world is real copper-nickel-chrome plating on plastic. But the capital cost is huge (close to a million dollars for even a very small line), and that technology has its own steep learning curve as well. Good luck.

This website is wonderful!

A. Manny Saavedra
1. The base coat is developing goose bumps?
Do you spray the base coat by gun, or dip your products into tank? Sometimes spraying the base coat it is very easy to get many bumps.
2. The silver becomes yellow?
Have you used stability chemical S, and how long you put the chrome layer in the air?
Above is very important.

A. Yellowing or tarnishing can occur by means of a couple of things firstly the chemicals your using are out of date they should be clear (look at the activator if it is a brownish colour before you use it think what it will do if you spray it) secondly your water must be pure any contaminants salts minerals, etc. will all effect the result.
hope this helps.

A. I had the same problem, try misting/fogging the clear coat, by that I mean you instead of spraying the clear coat directly onto the chrome paint have your gun/aerosol spraying over and not onto (like dusting) the paint. Oh, and leave the paint to dry for at least 48 hours; paint dries on the top but cures outward and that can take up to eight weeks.
Hope this helps

A. We have spent the last year in a consultancy to investigate the above problems. The main problem of discolored silver is due to problems with the strength or formulation of the Reducer component; additionally the sensitizer solution's formulation also effects this area. First check that you are correctly diluting your stock solutions before spraying. Sometimes reducing the strength of the reducer buffer mix compared to the silver solution helps. Frankly the accuracy with which some suppliers make up their product seems very variable!

Rest assured the basic aerosol silvering system can be made to work reliably but in order to do so there has to be attention to detail right from the start of the manufacturing process to the final spraying; any error of formulation or contamination of the solutions results in defects.

A. Hi,
I am not an expert on chrome, nevertheless I am assuming top coat and base coat are liquid coatings. Therefore, the way you describe your problem makes me think that the base coat and top coat are not manufactured from a water white resin system. It therefore follows, as additional coats are added the darker the colour. If this is the case, ask for a pure acrylic based material as these are normally water white in colour, this should overcome your problem.

A. Hi, Oscar. The basic routine for chrome-look spray paint includes a base coat, a bright coat with either small aluminum flakes or the two-part silvering previously discussed, and a clear coat. Getting smooth consistent results will probably also require proprietary wetting/sensitizer/activator processes at the vendor's suggested points in the process, because this is not house paint that can be slopped on, but requires dealing with the surface tension between different layers. A couple of brands are shown in the banner ad at the top of the page. As mentioned, googling for "Brashear process" will get you started, but the manufacturers have put in years of research optimizing this process for use as chrome-look paint, and the product of that effort is trade secret, not public domain knowledge. You'll be years behind if you don't use proprietaries. Good luck.

Regards,

A. Hi, David. We don't recommend one supplier over another in this forum (huh? why?), but you say you can't get help from the supplier, so see if another supplier has supplies that are compatible with the spray system you have. Banners for a couple are at the top of the page.

Regards,

A. Hi, I'm Dave from SC, what we have found is water has to read 000 on a tds.

Next if it's sticky outside, heat each part with a hair dryer ⇦ this on eBay or Amazon [affil links] right before the clear; it's a balance: you do not want to overheat the part (the clear will dry too fast making it hard to get a gloss) also a good paint kept around 85-90 deg and you must control the wetness in the air.

Hello everyone -- hearing about the chroming process problems took me back in time to the exact day that I put all my money in a trash can. The spray on chrome is so sensitive and full of hidden tricks that as far as I know 8 of every 10 buyers quit in the process. Every single spot, tarnish or yellowing puts you back another 1,000 dollars, buying kits hoping that the next one is the good one. Sorry but it is true, and there are at least 6 persons in PR that can prove it.

Hello Zain. The basics are common knowledge and have been explained on this page. But the fine details for optimum chrome-look paint remain proprietary.

If, as the first step, you tell us the not-fully-successful formula you arrived at after all your work, hopefully someone will reveal what changes they made to further improve it. But people guard the fruits of their labor and I don't really think the first step will happen, let alone the second step :-)
But good luck.

Regards,

  Hi Balbir. I think that one of the issues here is that a number of companies have put a substantial amount of costly development effort into their chemistry, and they sell the chemistry plus technology as a proprietary package. We can't expect those companies to simply give us the fruits of that effort for free; so we'll probably see their licensees enjoy more success than others can achieve initially from lesser efforts.

Still, most technologies gradually evolve from proprietary to generic, and people are achieving ever increasing success with home-brew. We have many threads on this site about chrome-look paint. Marvin Sevilla has been exceptionally generous in sharing what he knows about it, so please search the site for "chrome-look paint Marvin Sevilla".

But if you have learned a bit in that 2-day course, and want to encourage info exchange, it's always best to start by volunteering something important that you've learned, even if you've enjoyed only partial success. "My formula is thus & so, but it is giving me the following problem ..." is way, way, more effective in attracting responses than "Please tell me your formula". We have dozens of open questions on the subject, some of which you might be able to help with :-)

Luck & Regards,

A. Hi, cousin Sajeesh. Exactly what does "related to chrome spray" mean please? Applying spray chrome is one thing, but building a chemical formulation house is a totally different one.

If you intend to apply the coating, please buy proprietaries. Most people wouldn't even formulate their own house paint or car paint, let alone the 4-coat system required for spray chrome (base coat, activating wetter, silver nitrate plus reducer layer, and hard non-yellowing topcoat). Some chrome spray is aluminum flake rather than silver-based. Even people with years of experience like Martin Sevilla warn us that such attempts are a foolish exercise. But please study this thread, and threads 26415, 33074, 35373, and 56727 ... or you might search the site for "chrome-look paint Martin Sevilla".

If you will be formulating your own silver nitrate layer, please give us some hints about the final topcoat layer to be compatible with it, durable, and (per the main thrust of this thread) non-yellowing. What are you doing for that? Thanks!

Best of luck!