How To Polish Bronze

how to polish coins

Many new owners of traditional boats ask the question: "How do I make my bronze shine like new?"  The most common and considered answer is: "Don't!"  Polished bronze is admittedly beautiful, but the patina which forms on its surface is protective, preventing further corrosion of the underlying metal.  Have you not watched "Antiques Roadshow," and seen how some priceless piece of art is made worthless because of an obsessive compulsive's need to polish it to a gleaming finish?  Plus, when you polish anything, you are removing material.  It may not seem like much, but over time you will have less and less to polish.  That said, let's assume that you still want a golden gleam on all of your bronze, and you are not in love with the idea of "going green" - just don't say we didn't warn you!

Though there is a whole family of copper alloys that use a number of different metals, and the names bronze and brass seem to be interchangeable and a bit confusing while on land, the difference between the two metals on a boat is critical - as you may have already learned if you've used cheap brass screws instead of the expensive bronze ones.  Basically, brass is copper and zinc, while bronze is copper and tin.  More metals or metalloids can be added, creating things like silicon bronze, but that is the general distinction - tin or zinc.  As you know, zinc corrodes rather quickly in the marine environment, as in "sacrificial zinc."

It's been said that "brass has no place on a boat except for the bell," but in fact the best bells are made of bronze, so brass really has no place on a boat at all.  Bronze was the metal of choice before stainless steel took over above decks, and is still the metal of choice below the waterline except for, perhaps, the prop-shaft.  If you have a traditional boat, chances are you have a lot of bronze aboard, and the reason for this is that bronze is incredibly corrosion resistant - particularly in the marine environment.  The patina which forms on its surface is very durable, which also makes it difficult to polish.  So, your best approach is a multi-step one.

Step 1:  What do you want on your fries?

Step 2: Elbow grease.

If you want to be clean and ecologically green, baking soda is a reasonable abrasive, white toothpaste works as well.  You can also make your own polish with pumice powder mixed with a bit of olive oil or water.  Your easiest solution, however, is to get whatever metal polish is cheapest at the hardware store, as it will have chemicals (mineral spirits, ammonia, urea, ethanol) that help break down dirt, grease and oxidation, as well as some form of grit to help cut through the patina.  Some popular polishes are Brite Boy, Flitz and Nevr-Dull, but there are many more.  They all basically do the same thing, though some brands have a "protective" residue which is usually oil and/or wax, and doesn't work for long when faced with salt spray and direct sunlight.

Depending on the size and shape of the object, you can use polishing wheels, buffers, Dremel attachments, and/or do it by hand.  In most cases a commercial metal polish will give excellent results within a reasonable amount of time, as long as the object has been polished since it was cast.  If it hasn't, you may need to use different grits of polish - starting with medium and working your way to extra fine - in order to get to where it gleams.  For instance, a cowl vent is going to be a lot easier to polish than a plumbing fixture.

Eventually, you will have that golden, mirror finish you were hoping for.  It will look absolutely beautiful on your boat, and people will literally stop in their tracks on the docks, gasp, and exclaim their admiration.  Varnished teak and polished bronze are, of course, what create the quintessential look of a bristol yacht, and stainless steel is a poor substitute.  Within minutes of exposure to salt air, however, the shiny bronze surface will begin to oxidize, and within days your bronze will be right back where it was again.  That's why there's step 3.

Step 3:  Seal it!

At every boat show there is a new miracle solution for the sailor who wants to keep his bronze shiny.  Most are simply oils and waxes that will only protect your bronze until the check clears, but some are more of a clear paint.  The problem is that lacquer doesn't last well, nor does epoxy, nor do the two-part fluoropolymers (similar to teflon) and other industrial applications.  They work great

in the home environment, and even below decks, but the sun and salt spray will eat them up.  Sure, they're better than nothing at all (though some actually contain chemicals which tarnish the metal beneath them, creating that "antique" bronze finish), but you can't expect to find anything in a spray can or paste that will keep your bronze looking freshly polished when exposed to the elements like you'll find on a salt-water boat's deck.

Recently, some have tried clear two-part polyurethane (LPU) with UV blockers and have had slightly more success, but the lack of "tooth" on the polished bronze means nothing you paint on will want to stick to it.  So, you'll be dealing with chipping and peeling down the road, and this will look far worse than an even patina - trust me on that one!  All hope is not lost for those who wish to keep the gleam without stainless steel or chrome, but the solutions are not perfect, and they're gonna cost ya!

In touring high-end docks and classic yachts over the years, we've seen only two methods of bronze protection which seem to work well, and they can only be applied by someone with a lot of know-how.  They also only work on areas that won't be abraded.  This means that working winch drums are out, as are fairleads, chocks, cleats, or anything else that is rubbed, knocked or even handled very often.  These are, therefore, "decorative" coatings.

The first method is clear powder coating.  Powder coating is applying an electrically charged powder to the object, and then baking it on.  When the powder melts, it forms a strong plastic film which is much tougher than paint. If a clear, UV resistant powder coating is expertly applied, it can last a long time. However, once it starts to go, it is a bear to remove.  While a perfectly glossy piece of bronze looks spectacular, a partially oxidized one with streaks of different colors looks much worse than an even, natural patina.  Again:  Trust me on that one.

The second method is even more costly than clear-coating, but the results are incredible.  It is gold electroplating - which means coating the entire surface with a thin layer of gold.  The object is super-cleaned, wired with a negative charge, and dunked into a vat of electrolyte with a positively charged anode. Gold moves from the anode and/or electrolyte and adheres to the surface of the cathode (your hardware).  This may sound familiar, since it is the exact opposite of galvanic corrosion.  Your zincs are anodes, the salt water is the electrolyte, and every other metal below the water line is (hopefully) the cathode.

Gold is soft, but it is almost corrosion proof.  So, anything coated with gold and left alone will stay looking good for quite a while.  Just don't let anyone polish or clean it with something rough - even a paper towel - or you'll have to plate it again.  This is the ultimate coating visually, and the fact that people are looking at gold and not bronze can just be your little secret.  It is possible to play mad-scientist and use an old aquarium (remove the fish!) or something to make your own electroplating vat, but since some nasty cyanide salts are usually used in the electrolyte, this is best left to professionals.

Now, after reading all that, you may be more likely to want to keep that nice patina after all.  If so, good for you!  The whole reason why bronze is used on boats is that it is so maintenance free, after all.  Embrace the green (or oil it to an even brown) and realize that it marks your boat as belonging to an old salt who knows his spanker from his baggywrinkles.  Tie a few Turk's heads in conspicuous places, get an eye patch and maybe a parrot, learn a few antiquated nautical terms (like spanker and baggywrinkles), and you're all set.  If you can play the part, you might even be able to let your teak go gray without hearing those dreaded words "neglected boat."

As a note:  If our other how-to articles are any indication, we will now receive a bunch of emails from companies who feel they have a product that will keep bronze shiny for months/years.  YachtPals will be happy to test and report on any bronze cleaner or coating a manufacturer would like to provide (as long as it doesn't require too much blood, sweat, tears or lost brain cells to apply), but be warned:  We won't pull any punches if it doesn't work as advertised. This is what we tell the companies that write us, and it probably explains why why we haven't had any takers on our offers of product testing.


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