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What IS Gunmetal?...

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Martin Field03/04/2016 23:15:32
68 forum posts

I'm confused....It ain't difficult<G>

I always thought gunmetal was a bronze, but I see castings these days described as gunmetal and they're grey things, like cast iron.

Could someone explain please?

Thanks,

Martin

daveb03/04/2016 23:22:12
631 forum posts
14 photos

They did make guns out of cast iron but Gunmetal is bronze.

Dave

MW03/04/2016 23:23:48
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2052 forum posts
56 photos

never heard of "gunmetal grey"? probably the zinc, tin or lead giving it that colour but you are right, it is a type of bronze. Mainly composed of copper just like traditional bronze.

Edited By Michael Walters on 03/04/2016 23:25:13

Martin Field03/04/2016 23:24:08
68 forum posts

That's what I thought, Dave, but I've seen a lot of stuff where clearly grey castings are called gunmetal.

Martin

julian atkins03/04/2016 23:25:01
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1285 forum posts
353 photos

Hi Martin,

Others far more expert than me will no doubt comment, but a small increase in the tin content affects the colour.

I have seen this in bellmetal (on new Church bells freshly turned internally), and gunmetal and bellmetal are not very different.

Cheers,

Julian

Nick_G03/04/2016 23:26:13
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1808 forum posts
744 photos
Posted by Martin Field on 03/04/2016 23:15:32:

and they're grey things, like cast iron.

Martin

.

Cut into and past that outer skin an it will (should) be a bronze / brass colour. This was probably left in the casting stage.

My understanding is that gunmetal is a blend that sits between brass and bronze. But I may be wrong.! But there are many grades of brass and many grades of bronze.

Gunmetal was originally what it says on the tin. It's specification and proportions of different metals was determined and laid down by the admiralty.

I am sure google will be a wealth of information on the proportions and differences between.

Nick

John Reese03/04/2016 23:29:49
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1071 forum posts

As Nick said, gunmetal is a bronze of specific composition. Don't remember exactly what they were. As cast it does have a greyish color. Cut surfaces are the color we normally associate with bronze: yellowish. I expect that if left to weather it would get a green patina.

Edited By John Reese on 03/04/2016 23:31:49

Edited By John Reese on 03/04/2016 23:32:36

Martin Field03/04/2016 23:30:25
68 forum posts

So, if I ever did get soft and actually buy castings for an engine, I should expect the bits described as brass to be just that and the very grey bits to be not steel or iron, but disguised bronze?

Cameras must be less good at colour than I thought!

Thanks for the assurances.

Cheers,

Martin

Michael Gilligan03/04/2016 23:31:35
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23121 forum posts
1360 photos

Martin,

Your confusion is understandable

Here's a quote from the Wikipedia page:

Gunmetal as a color is entirely different to the reddish alloy of the same name described above. It is a shade of grey that has a bluish purplish tinge.

... I think Nick_G has summed it up.

MichaelG.

Martin Field03/04/2016 23:36:19
68 forum posts

I could see that the skin has a strange colour thanks to the heat of the casting process, but not once it was being machined. Wiki reckons its copper, tin, zinc and lead. So brass with a bit o' tin chucked in, just about 5% apparently. So, why, I wonder, do Mount casting sets come as both gunmetal AND brass if they're so close in make up. (Although I once turned a 1/6th scale Matchless crankcase in bronze, thinking it brass). For ever!

Cheers,

Martin

Nick_G03/04/2016 23:36:46
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1808 forum posts
744 photos
Posted by Martin Field on 03/04/2016 23:30:25:

So, if I ever did get soft and actually buy castings for an engine, I should expect the bits described as brass to be just that and the very grey bits to be not steel or iron, but disguised bronze?

Cameras must be less good at colour than I thought!

Martin

.

Here is an image of the casting kit of the Stuart No.4 I recently made.

The difference in what is what should be obvious.

Don't be so quick to blame cameras tonal capabilities. It may be your screen settings.

Nick

Michael Gilligan03/04/2016 23:38:43
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23121 forum posts
1360 photos

The Tin makes a lot of difference to the mechanical properties.

MichaelG.

Martin Field03/04/2016 23:40:21
68 forum posts

Well, I might guess that the standard is bronze, the bright bits brass, and most of the rest steel/iron. But I'm sure you'll tell me otherwise?

Martin

Nick_G03/04/2016 23:45:12
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1808 forum posts
744 photos

.

This is bronze that I machined last week.

It's PB1 grade so only a small step away from gunmetal.

Nick

Nick_G03/04/2016 23:48:17
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1808 forum posts
744 photos
Posted by Martin Field on 03/04/2016 23:40:21:

Well, I might guess that the standard is bronze, the bright bits brass, and most of the rest steel/iron. But I'm sure you'll tell me otherwise?

Martin

.

No.!

The standard is cast iron along with all the other dirty scraggy looking bits. All the bit's that look like brass ain't. They are gunmetal.

Nick

Paul Lousick03/04/2016 23:50:45
2276 forum posts
801 photos

The color of gun metal looks similar to bronze when machined and is slightly darker in color than brass. It is very easy to machine. The base casting (upper left) is made of gunmetal and the spring retainer (middle piece with bolts) is made from brass.

0816 parts (medium).jpg

Martin Field04/04/2016 00:00:40
68 forum posts

So, Nick, the gunmetal bits are unmistakably NOT grey! I guessed bronze for the standard as it has a brownish tinge to it.

Well, well....at least I now know that if I buy gunmetal it'll be something other than cast iron<g>

I am unlikely to buy any of these things anyway, but I just HAD to find out.

Many thanks all.

Cheers,

Martin

A G04/04/2016 00:31:42
12 forum posts

Are they using a picture of the cast iron castings, where they are available as a CI or Gunmetal part?

JasonB04/04/2016 07:57:58
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25215 forum posts
3105 photos
1 articles

Its probably just an oxide layer on the surface. Think of a bronze statue they are usually a dark colour but any parts that get rubbed regularly are the yellow base matal.

Also if you have ever soldered GM or Bronze it will go that dark colour as it oxidizes

Another possibility if they are sand cast is that a mould was has been used on the surface of teh sand and that can leave a discoloured surface.

Edited By JasonB on 04/04/2016 08:00:42

Martin Field04/04/2016 09:35:23
68 forum posts

I've just checked the pictures in an old Model Engineer in which the series was run and even in the lathe, the base looks as likely cast iron as a bronze colour, which is probably why my doubts came in in the first place.

Martin

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