Bronze Trophy Surface Finish

[Merlion]

I need help with a problem relating to surface finish of bronze castings.

This arise from my interest in submitting a design proposal for an award trophy. If I design it as casted bronze, I need to give it a good looking surface finish.

I understand it is not a problem to give a smooth finish to the bronze piece by fine grinding and buffing. After this, what patina or other treatment should I apply to the bare metal surface to keep it bright and shinny?

A related question is whether I should go for highly polished brass and apply some coating to keep the shine.

[Daniel]

Hi Merlion,

I think that often awards are plastic that has been plated with brass or whatever to give it that very shiny surface. At my job we produced some life-size Star Wars C3-PO replicas several years ago, and they had to have that super-shiny brass appearance. The replicas were just fiberglass. We had to coat the fiberglass with Duratec polyester primer and sand them to a very smooth finish. These parts were then sent to be metal plated. They came back with that finish you are probably looking for.

Here is a website that explains the process:
http://www.bergen.org/AAST/Projects/RapidPrototyping/index.html

[nep75]

After a LOT of elbow grease polishing the bronze or brass to that shiney finish, you could oil it or find a gloss laquer, or really buff up a good protective finishing wax - that would help protect that look. I still don't think it's going to look like that shiney plastic brass award finish though. But if it's going to be a bronze then a darkening patina would look nice. The highly polished sections of the real metal won't take the patina as well so they can be buffed back to the shiney with a little more work.

~ N

[fritchie]

Merlion - Most of the "bronze" trophies I've seen are plastic, coated in some way to look like bronze, probably similar to the methods posted above.. Must your trophy be in actual bronze? That will be quite expensive.

[Merlion]

Merlion - Most of the "bronze" trophies I've seen are plastic, coated in some way to look like bronze, probably similar to the methods posted above.. Must your trophy be in actual bronze? That will be quite expensive.

I am aware of this. The awards for these trophies are quite prestigious. Thus the organiser plans to have two sizes of the same design costing US$200 and $150 each. For me, I look into bronze casting due to my lack of experience with other relevant materials/techniques. I suppose the same foundries can also cast brass.

I've checked on the price of my own bronze castings done over here. The intended price is within possible range.

Incidentally, I understand tin pewter castings for art deco items are or have been done in neighboring Malaysia, being a tin producing country. Glass casting is also a possibility. But for both these techniques, off hand I don't have the contact and experience. I may find out more about them in future.

But

[Merlion]

From what I can find out, a clear lacquer is applied over polished bronze to protect the bright surface. It does not look as good as the uncoated surface, but it prevents oxidation.

A good wax polish will also protects it for a reasonably long time indoor. Probably this looks better.

My next question is comparing polished brass and polished bronze, which one is better for a trophy, and why?

[fritchie]

Merlion - Bronze is considerably harder than brass, and thus less likely to deform. Conversely, bronze would be more likely to crack if treated very roughly.

You also should look into the various alloys, if you are able. Sculptors I know in this area use only silicon bronze, an alloy about 96% copper, 1% silicon, and 2 - 3 % of either iron or a different transition metal, possibly manganese. (It's been some time since I looked at the composition.)

And brass also comes in many alloys. Classically bronze is an alloy of copper and tin, with brass being an alloy of copper and zinc. Today, there may be twenty or more alloys in each category, each with specialized uses.

[Merlion]

Thanks Fritchie for your information and advice about bronze and brass suitable for trophies.

I am still pursuing my investigations and tests on this matter. To observe what polished bronze looks like, I took out my first bronze casting, and sand and buff polish it. I'm glad it looks a bit like polished gold, see below (pardon the flaws in the casting; it's just a test).

I plan to coat it partly with wax and partly with clear lacquer to see the difference.

[Merlion]

For those interested, I have put canola wax on half of the polished bronze. As expected, I cannot see any difference.

On the other half, I sprayed clear lacquer. Spraying may not be the best way, but it is just for convenience. In general, the shine is reduced. For some reason, one part looks worse. The photo below shows this bad portion. At the bottom, the shiny portion is not sprayed but covered with wax.

[fritchie]

Merlion - You say the piece looks like polished gold, but the pictures come across on my monitor as essentially white, with some yellowish or goldish tints in partial shadow. Is this an artifact of the photography? Or are the pieces more or less white?

By the way, since gold almost never is used as the pure metal, it comes in many "colors" itself: white and red are two descriptions I've seen. The red I've seen really does have a reddish tint. The white I've only seen in watches, and it is a lighter yellow than typical.

[Merlion]

Fritchie,

The color of my polished bronze piece is like polished gold in gold jewellry. It comes out more or less the same color in my photo as well as my computer screen.

To help illustrate, I attach another photo from my foundry showing me an example of a dipped gold statuette. Unfortunately this photo is a bit greenish in general.

Or else, here is a link (http://www.goldringsplus.com/) to many pictures of gold rings (drag the mouse over the text).

What color do they appear on your screen?

[fritchie]

The jaguar in your post is close to what I would expect gold to be - mostly a pale yellow, with other shades from reflections. The rings mostly are light yellow, some slightly on the orange side. I think the reason your original photos come across as mostly white is a matter of contrast. The gold foot is by far the brightest object in a photo that overall is much darker.

Using a much lighter, even white background for your sculptures might give a better gold color on monitors. I'm not trying to tell you how to photograph your work, but I know you are very meticulous, so I wanted to give some feedback. Best wishes in this project.