Thursday, August 03, 2006

Reforging Iron in Pictish Scotland - Number Two

Evelyn is researching background for a novel set in the Viking Age. This is my second set of answers to questions she has posed. For those technical experts out there, remember this is pitched to someone who has no training in metals and has been getting often conflicting information off the web.
I'm including this edited version on the blog mainly because some of your might find the answers of interest...

> The candle sconce I referred to would be found in a monastery in Eastern Scotland

My suggestion here is based on the fact that candle sconces have one historic problem:
You just do not find what most people think of as candle sconces during the Viking Age.
There are a couple of very small and very simple candle holders - not much more than three short bars as legs that are joined together and have a spike to hold the candle. There is one set of oil lamps from Oseberg (Norway c 825) which are a long bar about a meter long with a small dish to hold oil on the end. These are ROYAL quality objects.
So the classic looking long bar upright with legs and candle cups just does not exist in pre Conquest Scotland.

>I'm wondering if you'd have an opinion on whether the sconce or similar would be likely to be pig iron (and hence soft) or a harder quality of iron - given the times.

Pig Iron is part of a technology that is most definitely POST MEDIEVAL. Entirely the wrong method for the Viking Age - this technology is several hundred years into that future!
Pig Iron refers to a method were the rock ore is converted into the smelter into a high carbon, liquid CAST IRON. This metal is tapped out of the smelter and let run into channels dug into a floor covered with sand. The individual blocks radiate out from a central line in a shape suggestive of piglets suckling - thus the blocks are called Pig Iron. The term thus refers to the shape of the block - not the metal content.
On top of this, the metal in a pig is high carbon cast iron. You can not forge this metal - it is extremely brittle and one hammer blow will shatter it into small fragments. In the Dark Ages such cast iron might be produced in a badly controlled bloomery smelter. Since that metal could not be further worked by forging - it was considered spoiled and may have been recycled. Note that the Chinese figured out how to work with liquid cast iron many centuries before this was achieved in Europe.
Ok? - you are looking at post 1600 or latter technology here.

>.. would make a lousy knife and sword because it would be too soft to hold an edge. And I imagine there would be a lot of skill required to pattern weld pig iron with a stronger iron or steel to forge a blade, so... it makes more sense for the character to reforge something of a better quality of iron.

Remember that the metals you have available to the Viking Age are all formed in a bloomery smelter. The primary material will be similar to wrought iron (Which if you get really technical actually a specific physical method which is roughly post 12 - 1300 AD).
But lets not write an archaeological report! Lets say most objects are forged from wrought iron, which is soft as you say. Not the best thing for a weapon.
Bear in mind however, that the selection of metal hardness available in the Viking Age is not like today's selection of A / B / C. In the VA, there would be a range of hardness (carbon content) between individual pieces in a pretty much random basis. Even one bloom mass (ore to metal in the smelter) will have graduations across it.
Now back up. Because of the random nature of the starting metal, and the high cost in terms of skilled labour required to turn ore to metal, the range of quality in early period knives is extreme. The carbon content (thus the hardness and edge holding) varies a lot. Again, the point of reference to the Dark Ages person is quite different than our modern one!

>Any suggestions what this might be - given the monastery theme?

You might consider that large objects of iron were in fact extremely expensive and difficult to construct. In short - high status objects. Forged iron staffs as a symbol of wealth or position are found from the Viking Age (Although these are linked to 'wise women' involved in the ritual of Sa∂er... its own long story.) A cross of forged iron would not be inconceivable as a status ritual object.
If you wanted a real kicker - have the source object be a 'crucifixion nail'. About the right size for a knife. If all the nails that are attributed to Christ were in one place - you could build a battleship!

> Also, I know the following (heat treating) processes are somewhat secret, however I'm not sure what the term "anneal" means.

Secret inside a Dark Ages context. Easy to find in outline in modern print! Heat treating has three phases:
Anneal / cool slow, / soften and remove stress
Harden / cool fast / hardens
Both of those are done from 'above critical' - for ease lets say at about blood red colour (about 900 - 1000 F)
Temper / low heat and cool fast / REMOVES some of the hardness
Temper is the least understood. This process involves heating the blade up gradually to some range between roughly 400 - 800 F. As this is done, a hint of colour crawls over the surface. Different colours relate to different amounts of softening. Depending on the tool and the metal used, you might want different hardness in different parts of the blade.
Typical for a heavy tool knife is using a mid carbon steel, quenching in oil and pulling the temper to straw on the edge and blue along the back.

> Would the forge fire be a different colour when it is cooler than when it is hot? (Blue when hot and orange when cool?). Or would it be guesswork given that he'd be applying less charcoal and pumping the bellows less quickly?

Yes - but you are using propane as your reference (blue?). Colour shift goes red / orange / yellow / white / brilliant white. Those are the metal colours btw. The smith is concerned with the change in the METAL - not the fuel.

> I believe the heat for reforging pig iron is 1150 degrees Celsius. Is a stronger heat required for a stronger iron or steel?

Too technical for your purposes. As the carbon content or alloy content of the metal changes to create a harder and tougher metal, the amount of heat you have to apply before you can have any effect when hammering also increases. In extremely rough form: you can work wrought iron red, mild steel orange and mid carbon steel dull yellow. As the alloy toughens you also have to do more work. A the same temperature, wrought iron the size of your thumb, mild steel like your ring finger and carbon steel like your little finger would move the same amount if hit as hard (again really rough estimate!).
Remember that no one could measure ANY of these temperatures absolutely until the Industrial Age - like post 1860's. Temperature is determined relatively, by colour. (Why blacksmith's shops are kept dark with few windows to achieve consistent light levels inside.)

> I'm also wondering about the shape of the tongs. Because they have to be long enough to afford the blacksmith protection from the heat as well as strong enough to hold the iron being forged... would they be scissor shaped? I couldn't find a picture of the tongs on the 'Adventures in Iron Smelting' page 23, (which refers to smelting tools for blooms) although reference is made to Bloom Tongs on page 24 and how the blacksmith's tongs from Norse finds are small. Are Bloom Tongs and Tongs one and the same?

Vast difference in size! The bloom tongs we use are based on VA style - but there are no artifact examples of that specialized type. The heat radiated out the top of a smelter when extracting a bloom is simply intense. Bloom tongs are also designed to grip a mass roughly the size of a football.
Look instead at the World of the Norse - Town House - Blacksmith's Shop. You could also search under 'Mastermyr Tool Box' - there is a very good reproduction made by a group of American smiths a while back that is documented on the web.

This is a set of hammer, tongs and currency bars I made for the L'Anse aux Meadows 'Encampment' program.

1 comment:

Weekend_Viking said...

Hi, Zane here, we corresponded earlier this year after my iron smelt over easter.

Is this author in Australia? - you advised her to seek out Aussie re-enactors in the first post. If so, I'm an Aussie Viking Age re-enactor (well, New Zealander, actually, but currently working in Australia) and if she's nearby (I'm in Canberra, but will be in Brisbane or Adelaide later this year) I could give her some demonstrations of VA gear in action.


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