Fun With 10 Amps and a Bucket of Caustic Solution

After pulling my bronze portlights a few weeks back I've been researching ways to clean them up.  What I originally intended was to have everything re-chromed, but I just couldn't justify spending so much on a cosmetic thing (over $1k for everything).  Anyway, I like the look of raw bronze in both the polished and patina'd forms so I started looking into the various cleaning techniques out there.

There are a lot of threads on wire brushing and polishing and generally labor intensive methods that I wanted to avoid because I am basically a lazy person when it comes to polishing things.  I had some recommendations that Muriatic (HCL) acid worked well and I even picked up a jug of it at Home Depot.  However, during my research I stumbled onto several forums that were devoted to metal platers (eveyone needs a hobby right?) and many indicated that strong acid on bronze can lead to bronze disease because the acid is an equal opportunity dissolver; it will just as happily attack the tin in the bronze as it will attack the chrome.

While on one of these forums I saw a few references to electrolytic de-plating and how it does a great job at removing chrome and rust and best of all, you don't need to spend hours and hours polishing and sanding.  After corroborating the method with some more research on the theory behind the method, I decided that it was worth a try and I had most of the materials/equipment needed already.

So before I describe what I did, I want to give the standard disclaimer when bad stuff could happen:  I am not responsible for any death, dismemberment, shock, hazardous waste, or anything else that could be construed as bad.  Just do your research and be careful;  the big risk is shock if your not careful and properly disposing of hazardous waste after your done.

The basic theory behind it is that you reverse the process that plated the chrome onto the bronze to begin with.  The result is that any chrome or rust on the part is removed over a period of several hours. The ingredients are as follows:

1. 12 volt battery charger
2. 5 gallon bucket
3. Several 2 foot lengths of rebar
4. Sodium Carbonate (Arm and Hammer washing soda found at grocery store)
5. A few gallons of water
6. A part to de-chrome
7. A few c-clamps
8. 2 feet of house wiring (romex)
9. Small length of wood to span the bucket.

To put it all together, do the following:

• Take 2 or 3 pieces of rebar and c-clamp them to the inside sides of the 5 gallon bucket
• Wire the rebar together with some of the house wiring.  
• Add a few gallons of water and add a cup of sodium carbonate to make the electrolytic solution.  
• Take another piece of house wiring, expose some of the  copper in the wire and wrap it around the part tightly (to make an electrical connection)
• Suspend the wired part on the piece of wood in the middle of the bucket so that the part is submerged.
• Connect the positive lead from the battery charger to one of the pieces of rebar and the negative lead to the wire connected to the part.
• Turn on the battery charger.

Both the rebar and the part should start bubbling in short order.  Remember that this should be done outside or a well ventilated area because the fumes are potentially toxic.  I left each part in between 4 and 8 hours before pulling it out.  When it first comes out the part will be black, but putting it in another bucket of water and give it a good scrub with a scotch brite pad will bring out the bronze shine.  All in all it is WAY easier than trying to polish or wire brush them.

Before and partial after

Final product

So far, I've only done one portlight and an anchor chain hawser, but the results are incredible.  I think I could have left the portlight in a bit longer because there are still a few sections of chrome (or possibly nickel) that proved to be pretty stubborn to remove.  I may buff these out or dunk it again at some point but it's good enough for now.
Another word of caution: what I've read is that the bi-product contains hexavalent chromium (of Erin Brockovich fame).  It should be disposed of properly and I have an empty 2.5 gallon screw top container that I plan on using and bringing to hazardous waste day at our dump (they hold it periodically).