Friday, February 05, 2010

Smelting with Sven & Yorgi

Now, this is what I remember from smelting with Uncle Sven and Uncle Yorgi:

You first will need to build a bellows, one larger than the one a blacksmith uses.
This bellows should have each plate about one span wide at the hinge and a span plus a hand at the handle end. The plates should be three spans long. The lift on the bellows needs be about two spans (A). A bellows such as this will make the right kind of air for a smelter.

There are a few other special tools that you will need to forge out before smelting iron:
- A long rod, about the size of your little finger with flattened corners. This needs to be long enough clear down the inside of the tuyere tube, at least three spans long.
- A heavy rod, about the size of your thumb with a short chisel tip on one end of it. This needs to be long enough and heavy enough to drive down inside the whole smelter from the top, perhaps two ells. It may be needed to pry free the bloom.
- A heavy rod with a short flat hook on one end, that about the length of three fingers. This can be set to a wooden handle, but the last two or three spans must be of iron. It is used to hook under the hot bloom inside the furnace.
- Very large tongs, with good long handles. This needs to be big enough to pick up the bloom, and to do so down inside the smelter.

You will need a good pile of charcoal, depending on how big a bloom you want to make. As the charcoal for the smelter can not be too big, make your charcoal using sticks about two fingers wide. After it is cold, break the pieces so they are no longer than that same width. You will need at least 30 or 40 buckets (B) of charcoal, double that much for a big smelt.

You will need to gather some bog iron ore. Not all ore is as good as others. You need a bucket of ore to get any iron bloom at all (C) , so it is best to have two or even four times that much on hand.
It is best if you roast the ore first. Make a wood fire on a fresh bed of sand. Once the fire is well lit, put a row of wood splits across the fire. On to this pile your dry ore. Once the fire has burned cold, you can pull out the roasted ore from the ashes. The pieces should not be too large, break apart any much bigger than the thickness of your thumb. When you start adding charcoal to the furnace, make sure you add from the top of the pile. (D)

You need to build the furnace out of clay. It should be at least a span wide on the inside, maybe a bit wider. The walls should stand so tall that you can just touch your knuckles to the floor of it, with the top of the wall to your arm pit when you reach inside (E).
Now, depending on just how you build it, will tell you how thick to make the walls. If you do not have much clay, you can dig back into a bank of earth. Then your walls just need be thick enough to hold the fire in, about two fingers thick. If this furnace is to stand up on its own, it is better to make the thickness of the walls at least three fingers, even better four.
If you want this furnace to last for several smelts, or to keep from cracking, it is best to mix your clay with some chopped straw. Cut your straw with a hand axe to pieces the width of your hand, and mix the same amount of clay and straw. If your clay is too wet, you can add some beach sand to make it stiffer.

The best thing to do is let your furnace stand for a day or two to let the clay harden. To keep the walls from sagging, fill the new furnace with dry sand or ashes. This is easy to scoop out to clear the furnace before you start the smelt. If the furnace stands on its own, laying some flat stones around the outside will make it keep its shape. Put some sand mixed with ashes into the spaces between the stones and the walls.

Once the walls have started to harden, two holes should be cut. One is a door right at the bottom of the furnace. It should be about the size of your hand with fingers outstretched. The other hole is for the air pipe, which should be part way around from that door. This hole is made just big enough for your bellows tube to fit. It should be two hands above the base. It is best if this hole is cut so the pipe will sit at an angle, pointing down inside the furnace, roughly one quarter off from square (F) It is best to set your air pipe in place before the clay is too dry.

Now this tube is best to be separate from that which comes out of your bellows. The tuyere can be made separately of clay, forged from iron, even hammered from copper. (G) It is best if the tuyere is the shape of a long narrow taper. The smaller end, inside the furnace should have an opening about the width of your thumb or a bit less . Your tube should sit so it is about two fingers proud of the inside wall of the furnace. Pack soft clay around it to seal the hole tight.

It is best to warm the furnace gently with small pieces of wood to dry all the water out of the clay. This works best if you open the door in the base to let the air in. This fire may burn a good part of a day, until no more steam comes off the outside walls of the furnace.

Once the furnace is dry, it is time to set the bellows in place, attaching it to the tuyere. The furnace door is shut, and the furnace filled with charcoal. Now the bellows man will start to pump, and keep pumping with the same strokes for all of the smelt. (H) The furnace will burn slowly at first, but still it should be kept full to the top with charcoal constantly.

You will know when it is time to start adding ore by looking for the fire to come up to the top of the furnace. The glowing charcoal should be seen about one hand down from the top before you start.
Now you add ore by the double hand full, one measure for each bucket of charcoal. Do not place the ore on in a big pile, but add it a bit of a time, all through the charcoal. For the first four or five buckets, add only one measure of ore. Once this has been done, and if your fire is burning hotly, you can start adding a bit more ore to each bucket of charcoal. (I)

As the smelt grows, it is important to listen to the air in the tuyere. If the sound becomes faint, check to see if the tube is starting to be plugged. Quickly break away the slag with a rod if this happens. If you hear a bubbling sound, look to see if there is too much liquid slag forming. You may need to open the furnace door and poke a hole in the bottom to let the extra slag run away.
This all continues until all your ore is done. Make sure to keep a couple of buckets of charcoal for the last steps.

Once all the ore is used, add at least one more full bucket of charcoal to cover over it as it falls inside the furnace. Then you let the furnace burn down inside until most all the charcoal is gone.
The best way to pull out the iron bloom is out of the top of the furnace. You might have to scoop some last burning charcoal out of the furnace, until you can just see the liquid pool of slag. Then take a log to hammer on the top of the bloom, which you will see sitting inside the slag pool, just under under the tip of the tuyere. This should allow you to use the bloom hook to grab under the free edge of the bloom and pull it loose from the slag. (J)

Now reach down quickly and pull the white hot bloom over to the stump, where your hammer men are waiting. Quickly hammer over the surface, knocking off any slag, which cools quickly. Then stronger blows will compact the bloom to a solid lump. If you have not broken your furnace, and if you added fresh charcoal when the bloom is pulled, you should be able to re-heat the bloom as you need to keep working it. Often the last step is cutting the bloom with an axe.
The notes indicated in the text will be included in the final paper.

This is part of the ever expanding work I am doing related to the Vinland iron smelt. For a number of reasons (wait for the paper) I believe that the smelt uncovered at L'Anse aux Meadows Newfoundland is the work of 'tool using farmers'. This as opposed to a smelt carried out by anyone truly well experienced in the methods. This should not be too surprising, considering that 'Leif's Houses' represent an exploration base camp, not a true settlement.
So this begs the question : 'Just what DID they know?'
Most likely these men would have taken part in a seasonal round of iron smelting, perhaps many years past. They would be limited to what they might have observed - and what they could remember.

The instructions above are perhaps too detailed, and they do represent a translation from memory to written record. They might best be considered also as having come from a much more experienced source (What Ketill told me about smelting iron).

A possible physical test of this concept (I remember from smelting with Uncle Sven and Uncle Yorgi) may make up a later experiment here at Wareham. Put three people in front of a pile of raw materials, then have them build a furnace and run a smelt. Ideally these would be people who are generally good tool users, and have been present at a number of past smelts here. Since the normal cycle for DARC is at best three smelts a year, these people would represent a fairly good substitution for those Norse farmers.

No comments:


February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

COPYRIGHT NOTICE - All posted text and images @ Darrell Markewitz.
No duplication, in whole or in part, is permitted without the author's expressed written permission.
For a detailed copyright statement : go HERE