Bright Dipping of Brass

A. Hi Marcello,
You probably can anticipate this first comment because you see it commonly on this site: "if you don't understand the measurement units people are talking about, you probably don't know enough to be working with those very hazardous chemicals". For example, if you spill a little of that nitric acid, how are you planning to wipe it up?

People really should have hands-on hazardous chemical training before working with this stuff. To tie that into your question about Ed Budman's and Jim Connor's comments: it is often unclear what units or purity or measurement method people are speaking of, and misinterpretations are commonplace, so it is best to have sufficient understanding and training that you don't do something really stupid based on a slipped decimal point or misunderstanding. But -- in general -- when people speak in terms of volume measurement they are probably not expecting you to use 100% concentrated chemicals, but the highest commonly available concentration. The phosphoric, nitric, and acetic acids are probably all of different concentrations. I think that's what Ed wanted, and Jim wants, you to use.

Moving on: when plating shops process parts they do not need to do the same primary "scale breaking" and "pickling" that a steel mill or foundry did. Rather, they use an acid to "activate" the surface by removing any light oxides so that the plating occurs on raw metal, not on oxide or tarnish films. But some people in plating shops will call this the "pickling" step. Because you will be blasting or polishing, "activation" is what you will be doing not any sort of primary pickling.

"Degreasing" is another piece of slang because the step is actually "cleaning". If you can afford the time to polish the parts, you can probably afford the time to clean them with a scrub brush, water, powdered pumice, and a dash of detergent rather than having to build a cleaning station and trying to formulate a cleaning chemical that will saponify, wet, emulsify, deflocculate, sequester, chelate, buffer, and inhibit :-)

So, blast or polish the parts, scrub them, rinse them, dip them in dilute sulfuric acid, rinse them, then plate them.
Luck & Regards,


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

A. Dear Alfredo , I recommend that you contact Macdermid and look at one of their products called Kenvert K35 it is a chemical polish for Brass & Copper, they also have another product in the Kenvert range called K 30 PR which also works well but is Chromic Acid based. Without more technical information about the actual process you are using, it is very hard to give specific advice. Regards, J

A. Are you using a leach pot in your rinsing after bright dipping? If not, try rinsing then dipping in a solution of about 2 lbs of caustic soda beads [caustic soda beads in bulk on Amazon] to 10 gallons of water, before a final hot rinse. Good Luck.

A. I am no expert when it comes to bright dipping of brass. Others could give a better answer if you listed the entire process with concentrations and temperatures. Also a better definition of your part and how you are racking it would help. Gut feeling is that you are not getting complete rinsing between the process tanks and a trace or film of the chemical is settling into a recess or low spot which is adversely reacting with the following chemical. Since the rest of the part is OK, it would be in the processing of the part as in agitation (solution flow) or rinsing. Stressed metal from forming could possibly be the problem. but I would expect the opposite side of the bad spot to be bad also if it were the problem. It could be a rough spot from the die that is holding the chemical also. No simple answer, a process of elimination. I would try one part at a time with different racking combinations to see if you could isolate the problem.

A. Here is a quick and efficient "old-time" bright dip for copper and brass. Make a mix of 85% by volume Phosphoric Acid, and 15% by volume Nitric Acid. Mix the two thoroughly. Use at room temp. When you put a part into it, as soon as the part becomes covered with fine bubbles - it is done! Although I would NEVER EVER recommend it, I have gotten my fingers in this solution and have had time to rinse it off before any burning was ever felt. This can make copper, "new penny bright." Good luck, and remember to treat the chemicals properly and with respect. Used carelessly they can injure, and cause safety issues.

A. The bright dipping of brass really depends on the alloy. Leaded brass in the phosphoric/nitric mixture will pit.

I used to find that the phosphoric/nitric mixture worked best ... electroclean/water rinse ... dry. In some cases water on the surface will add to a etched surface. I would submerge the part in the bright dip solution (room temp) until fully covered then hold the part in the air until it was foaming from the chemicals (good ventilation required regardless of method) then follow with a complete water rinse until all visible signs of bright dip are gone -- might be a minute. Pull this out too soon and you will etch the surface unevenly as the phosphoric's viscosity will remain on the surface of the part. A 70 °F and warmer rinse would really helped.

Electrocleaning is a better alternative if it's just for plating purposes.

A. For good shine on blackened brass material, try 58% of nitric acid with some common salt.

A. Hello Khozem....I agree that the nitric acid based bright dips are rather nasty to work with as well as to treat. A good alternative is 25% acetic acid [on eBay or Amazon], 25% nitric acid and 50% phosphoric acid. Warm it to 130-150 °F. This doesn't produce the deadly orange cloud we all know and love. It is also harder to over-etch the surface. The parts should be dry to avoid etching.

A. An alternative is to use 8 to 16 oz/gal chromic acid with 15 to 25% by volume sulfuric acid. Also proprietary materials are available.

A. Hi Khozem. As for preserving the finish once you obtain it, a dip in sodium benzotriazole [on eBay or Amazon] before brass lacquer might be ideal.
Luck & Regards,


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

A. Hi Prabhakara. Sodium benzotriazole is used as a preservative on record and CD masters and other brass and copper components and I don't think it will interfere with your ion plating process.

Luck & Regards,


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

A. It is possible to procure a brass bright dip from a plating supply house in Chennai that will brighten the brass base metal.

The part will need to be cleaned prior to dipping and rinsed well after the dip.

A. Jeff

The Phosphoric acid will need to be discharged per EPA regulations and the heavy metal in chemical form too.

Alternatively go for a Proprietary Peroxide based bright dip which leaves behind a very cosmetically appealing finish while creating a metallic powdery sludge which is metal, not chemical. Hence disposal is very simple, sell the sludge to a recycler. The chemical breaks down into slightly acidic water due to tiny sulfuric acid adds for pH control.

Regards,

A. There are a number of commercially available deoxidizers for copper and their usage depends on the final degree of brightness required. The maximum brightness can be obtained by using a peroxide based chemical polish which provides excellent luster and has good shelf life against further oxidation. This solution, when spent, is very easy to waste treat and remove copper metal.

Other non-peroxide processes will remove darken oxides but will not further brighten the surface. These processes generally require an anti-tarnish post dip to prevent further oxidation.

Regards,

A. Hi. You can buy that product as a proprietary which also includes a reagent to slow the peroxide's tendency to spontaneously release.

Regards,

A. It's hard to say whether it would work for your mix of parts, Matt, but sulfuric acid plus hydrogen peroxide is substantially less toxic than nitric acid.

A. Instead of sulfuric or nitric acid you can use (maybe ... you must try) acetic acid /hydrogen peroxide solution (3 parts peroxide 3% [on eBay or Amazon] to 1 part vinegar [in bulk on eBay or Amazon]/5%). Hope it helps and good luck!

According to some other sources even hot 10-25% citric acid [on eBay or Amazon] can be used. Hope it helps and good luck!

A. Hi Steve. My understanding is that a bright dip for brass requires an oxidizing acid because copper does not readily dissolve in mineral acids. There are a wide range of different bright dips available, so unfortunately the readers are not going to know what you used. One of the more popular approaches is a mix of sulfuric acid and hydrogen peroxide, where the peroxide is the oxidizing agent, and this is available as a proprietary with stabilizers added which slow the spontaneous decomposition of the peroxide. But there are other bright dips based on nitric acid. And there are some discolorations that seem resistant to any bright dip except chromic acid. Better are proprietary mixes rather than home brews, and if you can find out what was used, your customer may already be familiar with it. Good luck.

Regards,

A. Hi Ruth.

I'm not quite sure if I'm following properly, but bright dipping is only a surface treatment, and it should have no effect on the bulk of the metal. If done improperly it could somewhat etch or pit the substrate though.

Regards,

A. Have you considered the possibility of an immersion copper deposit? It may be that the copper concentration has increased too much.

? Please tell me what kind of brass you are using.
Regards,

A. Hi Steve. If the handles are not removable from the steel windows, I don't think chemical treatment is practical; then you might try buffing with a more aggressive polishing compound. If they are removable, most plating shops should be able to bright dip them for you if you wish. If you'd rather do it yourself, and you feel you are qualified to work with acids and oxidizing agents, there are suggestions above -- and Goran's idea for dilute acetic acid plus dilute peroxide sounds interesting to me, and safer than the alternatives. Good luck.

Regards,

A. citric acid is a very effective and safe way to remove tarnish from brass. If you want to do it in place rather than by dipping, there are products that will let you do this. (They are sold as stainless steel passivators, but they work for brightening brass all the same!)

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Ed. note: Hi Thomas. It's fine to ask for home-brew help, procedural suggestions, whatever. The only thing we don't post is suggestions/slams of specific brands and vendors (huh? why?)
One answer to the question of which brand/vendor of process chemistry is best that I often hear is: "the brand with the best local serviceperson". In my experience it is rather common that when a good local serviceperson changes employers, many of the shops he/she was servicing soon change over to the brand/vendor he/she now works for :-)

A. IMHO. If your distributor is not the manufacturer (as is implicit in your terminology) then ask the manufacturer for technical support. If neither the manufacturer or distributor can help you neither one deserves your business unless you are a very small shop.

A. Hi Arpit. Are you rinsing in deionized water? If not, you should. Even still bare brass will discolor over time, and it may be a vain hope that it will proceed uniformly, rather than start in spots which are 'different' for one reason or another such as not as cleanly rinsed, slightly different composition in this area, a galvanic hotspot due to stress, fingerprints after treatment, etc.

It's probably best to use benzotriazole to maintain brightness, plus a lacquer or clearcoat of some sort.

Luck & Regards,

A. Hi Ahmet. Gene Packman answers that question above. Good luck.

Luck & Regards,


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

A. Hi again. That solution is intended to be used cold rather than hot. The Canning Handbook ⇨
suggests 6 oz/gal Chromic acid, and 9 fluid oz per gallon of commercial sulfuric acid (sp. gr. 1.84) -- a little lower concentration than Gene suggests.

Is it possible that you are expecting this solution to deliver a full bright shine when that is not its intention or capability? The Canning Handbook says: "This solution is more restrained in its action than aqua fortis, but does not impart so bright a finish".

Maybe process some product through the chromic-sulfuric tank, then take it to the lab for some small scale experimentation with a sulfuric acid and peroxide mix? Although I would suggest that you use a proprietary sulfuric-peroxide bright dip, if it is not available, see Nigel Gill's detailed instruction on thread 49844.
Luck & Regards,


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