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topic 2593

Porous Pots to Clean Chrome Plating

A discussion started in 1997 but continuing through 2019


Q. Our client is using a "porous pot" for rinse water treatment. We need basic training in theory and operation. How do they work?

Gus [last name deleted for privacy by Editor]


A. Porous pots do exactly the same thing, and function in exactly the same way, as membranes. Now, if only I really understood how membranes work, I'd be getting somewheresmiley

You put a cathode in the pot, and an anode around the outside, and it oxidizes trivalent chrome back to hex chrome, while simultaneously attracting the iron and other metallic contaminants. I understand that chromic acid remains an anion while the other metals are cations. Exactly what the membrane or pot does for the electrode process I don't claim to fully understand, but I presume that hex chrome can't pass through while the cations can.

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


A. We had a chatroom discussion about this a while back, and it turns out that the AESF sponsored a research project on porous pots. Email them ( and ask for a copy of the report. The scientists spent some time in the report explaining the mechanism, and had data about the pore size and anode and cathode ratios that are important to the proper operation.

pooky tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania


A. Check the December 1977 issue of "Plating and Surface Finishing" (AESF trade journal). You will find an excellent article about porous pots, how they work, and tips on usage.

Jeff W [last name deleted for privacy by Editor]

Ed. note: Thanks, Jeff!

1999 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. How does the porous pot work? How to get rid of trivalent chromium?

daniel spatafora


Q. I'd like to know how many porous pots I need --

I have a workshop for the plating of plastic, and I have a 100 gal. tank of chromium etch. Where I can buy the porous pots.

Mario E [last name deleted for privacy by Editor]
- Mexico

To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.


Q. Presently we are using 3 porous pots to oxidize tri-chrome to hex chrome with very little success. We run the pots at 6 volts/200 amps. with 15% sulphuric acid solution in the pots. These pots are used in a chromic/sulphuric etch bath for ABS/PC plastics.Tank volume is 3,000 gals.

Any suggestions.

Keith Guppy


A. You do not say whose pots they are or what size they are or the total amount of trivalent you are trying to convert in what time period. Also , how new are they. The pores can plug up and efficiency drops way off. I suspect that your reaction with the plastic is generating a lot more trivalent than you think. An obvious solution is to go to more pots if three is not enough. On chrome plating tanks, we just used the plating solution in the pot and dumped it when it was slimy. You may have to dump the inside more often than you are doing now.

What does the vendor of the pot have to say?

James Watts
- Navarre, Florida

August 5, 2009

A. Not knowing how high your tri-chrome has reached my suggestion would be to increase your sulfuric to 30%. 15% maintains your opt range once it's reached however 30% will help you to begin to lower your tri chrome.

Tim Roy
Plating on Plastic - Nicholasville, Kentucky


RFQ: Dear sirs:

I need to know of suppliers in the USA of porous pot for hard chrome plating. Please indicate name of companies.

Thanks in advance.

Oscar Infante
- Santiago, Chile


Q. We hard chrome plate and grind and are currently using a porous pot in one of our chrome plating baths. I would like to know how to make a porous pot from scratch as opposed to purchasing one for each tank.

Howard Larsen
PLATING & GRINDING - Muncie, Indiana,


A. I seriously doubt if you can make one cheaper than you can buy a rudimentary model (from suppliers who make this product).

James Watts
- Navarre, Florida


A. If you really want a cheap system go to your garden centre and get a flower pot - not the plastic type but a proper old ceramic type. Thoroughly wash it with acid and alkali cleaners and leave it in soak for a few days, regularly changing the water. Stick a rubber bung in the drain hole and hey presto - a cheap porous pot. I have used one for a divided cell in a small plating bath using trivalent chromium without any major problems. I don't know how long the pot will withstand the process, but in the short term it worked. Don't tell the membrane manufacturers though, they may corner the market for flower pots and upset us gardeners!

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


Q. I work in a chrome plating shop. We use a porous pot to clean the chrome bath. Sometime , after sitting in the plating tank, the liquid inside the clay pot is clear and has a pH above 10.0. Any thoughts on what it could be. I made sure the connections were right.

Tom Abare
plating shop - Springfield, Massachusetts

simultaneous 2006

A. Check to see if your polarity is correct.

James Watts
- Navarre, Florida


A. What is the porous pot for and what is it taking out? What type of chrome plating are you doing (Cr (III) or Cr(VI))? Is the clear liquid still coloured or has it lost all colour?

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

How to check if the membrane of porous pot is working?

May 12, 2008

Q. Dear Sir/Madam,

Our company has used porous pot for 3 months to reduce Fe content in our ex Chrome plating solution. The composition of our ex Chrome solution are : CrO3= 280-290 g/L; Fe=7-8 g/L ; SO4 = 4-5 g/L. Our porous pot used membrane from teflon ceramics. We filled sulfuric acid 10% v/v inside the pot to absorb Fe from Chrome plating solution and we arranged the current about 100-200 Ampere. The result of using porous pot for 3 months confusing us. Fe content still high, about 6-7 g/L, but SO4 content increasing to 15-16 g/L. If there any possibility the membrane doesn't work well and not selective permeable to absorb just only Fe? What kind of membrane that really selective permeable to absorb Fe from Chrome Plating solution? Thank you.

Yonatan Effendi
employee - Cikarang, Bekasi, Indonesia

May 16, 2008

A. Dear Jonathan,

I heard that other than porous-pot system, in Northern America & Canada even Europe nowadays a lot of Hard Chrome Platers are using sort of Ion-Exchange technology to reduce Fe content in their Hard Chrome solution to maintain the efficiency, roughness,waste water treatment cost, etc.

Might be you can contact your chemicals or machinery supplier in your city/country.

Good luck

Best regards,

John Torr
- Hangzhou, China

February 23, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Please advise what type and size of ceramic pot to hang in the tank to remove tramp metals? Also, do I hang it in the tank when the tank is off or on and for how long? E.g., is porcelain advisable of just any on stoneware fine? Thanks, Greg

Greg Hoets
Hub hardchrome - South Africa

February 2018

A. Hi Greg. Certainly a glazed pot could not work, but Trevor says an ordinary clay flower pot can serve as a membrane for an experiment if it holds up to the chrome plating solution. Please google "porous pot for chrome plating" and consider purchasing a commercial system for the purpose.

We don't know where you heard about ceramic pots for removing tramp metals from the chrome tank, so we don't know what you are aware of and what you're not. But please follow the links on this page as a starting point then get back to us with detailed questions. It's an electrolytic filtering process, not just an ordinary filtering process. Good luck.


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

March 2, 2019

Q. We have a porous pot for rising of chrome plating but we have a problem. For pulling it out of the bath, we use a crane; but I want to see or know what is a better way to pull this out? if you can show me by film or pic, thank you very much.

Mahdi hasouni
Electroplating - tehran, iran

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