Strange stone with metal nodules, anyone got an idea?

[Galemys]

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I found this stone in the rubble of my company's garden. This gravel there consists mainly of quartzite and abraded flint.
The darker section contains small metal nodules and there is a lighter sandstone-like covering. The stone is heavier than you might expect of its size and is slightly magnetic when using a strong magnet.

does anyone regognise this? Is it a natural mineral/stone or is it just manmade slag?

Cheers,

Tom

 

[Mesquite]

Looks a bit like iron slag

 

[demographic]

Yeah, looks like slag from a furnace.

 

[Janne]

Check with your local Archeological society.
Could be a prehistoric furnace close by.

A friend in Mayfield discovered a Roman furnace in his garden after a rainfall. Turned up it was (then) the largest furnace in South East.

I do not think fairly modern furnaces would leave that much iron in the slag?

 

[SoldierPalmer]

I would of thought slag but the metal is in perfect condition

 

[Toddy]

Looks like clinker….that's a mix of the crud from industrial (for a given value of 'industrial') processing. Usually it's charcoal and minerals, grit, etc., and the remains of coal burning, sometimes with metal particles within the deposit. Clinker gathers around tuyere pipes and the like…the airflow inlets.

If it's lighter than you expect when you pick it up, then it's likely clinker. If it's dense and glassy looking, then think more slag. Slag is the mix of the compounds used to help the smelting process, the contaminants within the raw ores, and the debris from the firing. It's sometimes a scum that's tapped off before the metal is poured.
The little balls are iron slag spheroids…they're part of the refining process.

I'm no metallurgist, where's Dave ?

M

p.s. much slag and clinker is powdered and added to road making mixtures. Ground granualted blast furnace something or other it's called.

 

[Janne]

(I am no metallurgist) should there be traceable iron in it? Enough for it to be magnetic? Do the modern processes not squeeze out most of the Iron?

 

[Toddy]

Depends where and how it was made. Modern (Bessemer and open hearth, the latter is very effective at using scrap metals) processes are very efficient, but mind it's usually a smelting for steel, and once the chemists (and they are chemists ) are sure they've got the adjustants and the catalyst mixtures right for the desired quality, the furnace is poured. There is always debris of some kind and usually the debris does contain metals as well as mineral residues.

Yes, iron slag is usually magnetic. Clinker is a bit more hit or miss. It's the crud from around the air inlets and such like, like the tuyere pipes. Slag is often glassy while clinker is frothy….sort of. You have to have it in your hand to be really aware of the differences. There's a huge range of waste and by products from smelting. The shape, blooms ?, is often indicative of the age when finding this stuff. Every process leaves debris that skilled archaeometalurgists can use to interpret the process used. From bloomeries, to finery to puddling hearths. A lot depends on what they were making too.

I'm hoping Dave sees the thread and comments, or Andy Mac, one's an archeometalurgist and the other is a geologist with a lot of background in metalworking.

M

 

[Hammock_man]

Could it be a very very old Christmas pudding and the metal is whats left of 3 denari pieces?

 

[Toddy]

Aye, indeed
Those were originally silver though, and even later debased ones were something like 5% fine.

I'm not a numismatician either

M

 

[Janne]

Thank you Toddy the Wise for the information!

 

[Toddy]

Hah! wait and see if you still think that once Dave Budd's had a squint at thon lump of stuff

M

 

[Dave Budd]

My ears were burning

Everything Toddy said! I would say clinker, it looks too mixed to be exclusively smelting slag. But it could be slag if it feels very dense and heavy. The shape of the iron lumps loom like they were liquid, so i suspect foundry waste from casting rather than smelting, but would want a better look before committing myself

Most iron slag from ther romans and up is fairly homogenous and quite dense and glassy, the amount of iron will depend on how well the smelt went. Yes modern slag would have very little iron, but likely still some. Clinker will contain some slag as well as iron, silica and all sorts of crud depending on what the source coal was, the forge or furnace lining, the source of iron worked and any fluxes. Even my charcoal forges produce a little clinker

Clinker like that could be 20th century or much older (i found a thick layer of it next to an iron foundry in norwich once, it hink it was 16th or17th century, but i cant remember exactly). Is there anything iron working known locally? It may have just been a lump left from building upa road or other surface and originated many miles from where you found it. Any pottery or other datable debris found with your lump?

 

[Toddy]

You have no idea how reassured I am Cheers Dave

I live slap bang in the middle of the central belt. Lanarkshire now is very, very green and lush, though a bit overcrowded, but it was the iron and steel capital of the Industrial Scotland. The last steel works closed not so very long ago, and Ravenscraig lit up the sky when it was working. Iron and steel making slag and clinker were/are pretty familiar. Archaeologically, I know Roman from blooms (sintered but not worked…basically very iron rich lumps) that I've handled but I don't recall finding anything.

I did some reading though, and it's fascinating the way people got round the problems of reaching the melting points (they didn't they adapted technologies and the fluxes ) and removing impurities.
Most folks on the forum won't have archaeology text books to hand though, but many experimental archaeologists are happy to write up and put articles on line.
Like this one….

http://home.deib.polimi.it/alippi/Archeometallurgy.php

Somewhere there's a thread about the Viking technique of using iron pan soil and roasting it to create iron rich lumps that can then be worked, almost like meteoritic iron. I'll find it too if I can

M

 

[Toddy]

Piling up the links

http://www.bushcraftuk.com/forum/showthread.php?t=75688

http://www.bushcraftuk.com/forum/showthread.php?t=91288

http://www.bushcraftuk.com/forum/showthread.php?t=120603


We really ought to give this a shot

M