What IS Gunmetal?…

[Martin Field 1Participant @martinfield1]

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

[Martin Field 1Participant @martinfield1]

[davebParticipant @daveb17630]

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

Dave

[MWParticipant @mw27036]

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 Field 1Participant @martinfield1]

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

Martin

[julian atkinsParticipant @julianatkins58923]

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_GParticipant @nick_g]

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 ReeseParticipant @johnreese12848]

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 Field 1Participant @martinfield1]

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 GilliganParticipant @michaelgilligan61133]

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 Field 1Participant @martinfield1]

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_GParticipant @nick_g]

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 GilliganParticipant @michaelgilligan61133]

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

MichaelG.

[Martin Field 1Participant @martinfield1]

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_GParticipant @nick_g]

.

This is bronze that I machined last week.

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

Nick

[Nick_GParticipant @nick_g]

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 LousickParticipant @paullousick59116]

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.

[Martin Field 1Participant @martinfield1]

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 GParticipant @ag]

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

[JasonBModerator @jasonb]

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 Field 1Participant @martinfield1]

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

[Chris GunnParticipant @chrisgunn36534]

I have had gunmetal castings with a distinct greyish tinge, but easy to tell when you have them in your hand that they are in fact gunmetal. However maybe not so obvious from a poor quality picture in a magazine.

Chris Gunn (no relation)

[Martin Field 1Participant @martinfield1]

That's true, even though the hue of the photos was a goldish tinge, they still looked grey under machining!

Martin

[Russell EberhardtParticipant @russelleberhardt48058]

Gunmetal grey – the colour of old cannons that are well oxidised.

Admiralty gunmetal – a bronze used for casting cannons (and bits for model engines).

Russell

[Martin Field 1Participant @martinfield1]

That's the odd thing about it all. That gunmetal is these days more associated with grey. It's always been a descriptive of a car colour or a fabric.

It's only metalworkers who tend to know that traditionally, gunmetal is a bronze.

Martin

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