Wednesday, February 14, 2007

Making a Norse Cauldron?

This modified from a posting to NORSEFOLK - some comments on building a Viking Age cauldron.

(Sorry about the lack of additions the last week - I've been working on the revision to IRON SMELTING and things like digging my truck out from under a snow collapsed garage..)

Artifact cauldrons are all considerably THICKER than what modern metalworkers are generally prepared to work with. This because the sheets of metal had to be hand hammered out. We are talking thicknesses in the range of 3 - 6 mm.

The largest width of any piece is generally LESS than 20 cm. Same reason.

Mild steel as a sub for wrought iron would have to be worked hot at those thicknesses. I have done a couple out of 1/8" plate (a pain to cut) which is still only 1.5 mm thick in comparison.

I personally have been unable to source actual bronze sheet here in Canada. Any USA folks may be able to get it down there. Although you can work bronze hot, it is quite difficult (the stuff has a narrow working heat and gets brittle almost instantly below that temp). Be extremely careful about hot working many bronze alloys, as they can contain some real evil heavy metals. I would NOT recommend working with any scrap bronze that you can not determine the actual content of.

I have had fairly good results with thinner sheet copper and brass. Brass is a ZINC alloy and can only be worked cold. Copper is easily available as thinner sheet (used for roofing) and plate is available, and it is a dream to work hot. Also fairly easy to work cold. Be aware that the prices for industrial copper (and thus brass and bronze) have skyrocketed over the last 6 months (thanks to the Chinese). A full sheet of 3 x 8 feet in 20 ga copper (would make two large cauldrons) runs about $300 CDN new right now. (So figure those prices you saw on my web site - at least $150 of the large copper cauldron is just for the raw metal)

Copper and brass has the advantage of being quite easy to TIN solder the seams after riveting. Purchase a lead free solder used for water pipes (generally a 95 % or so tin alloy) for this.

I have tried bronze braising a heavy forged mild steel cauldron. I have done this three times - and had a real time of it each time. I think it has something to do with the different cooling rates and strengths of the materials (bronze and steel). So I'd say avoid this method.

I have done the cheat of MIG welding the seams of a segmented mild steel plate cauldron to keep it food safe. Takes a good hand with the welder for a clean job. As the seams are on the inside its difficult to impossible to grind them afterwards - so you need your first pass to be perfect. Its also painfully obvious that you have used a modern welding method.

I have had better cosmetic luck welding the OUTSIDE - then taking a fresh cutting disk on my angle grinder and grinding the welds flush. This allows you to leave the 'step' where the plates overlap. Note that this will make the pot water tight - but not FOOD SAFE, there are still cracks on the inside. Once the pot has been put over the fire for an hour the soot pretty much hides the weld and grind. You would have to look at less than 12 inches to tell how it was done (assuming a careful job on the steps required)

If you are on a real tight budget and willing to use a three foot rule for visuals:

Get an old stainless or aluminum cook pot.
Work the surface with a hammer over a trailer ball or even a rounded wood stump to knock off the crisp seams and batter it up a bit.
take an old screw driver or straight chisel and round the edged off a bit. Then work from the INSIDE back on to a block of wood to lightly score a set of lines to suggest the margins of the plates. Lay your lines out with a water based marker before you start. Its best to use a light stroke a couple of times - than hit too hard and risk punching through the metal and making a hole.
Next drill and set lines of rivets next to the lines. As the rivets are set tight - they should seal up again to keep the pot water tight.
Likely you will want to replace the wire bail handle with one forged from a strip of flat metal stock.

Again after an hour on the fire you have something that would be better than average for SCA use. Not good enough for museum work - but since the trade off here is a $5 yard sale pot and an hour's work. - against several hundred dollars for a correct reproduction...


PS :
I have made a good number - you can see samples of most of what I discuss above at:

Although I think you will find those prices fair and competitive, I give you the link because it also shows you images of a number of artifact cauldrons with the book references.
Be aware that all the UK companies that sell 'wrought iron' riveted pots are in fact using mild steel NO ONE uses actual wrought iron metal. Their pots all leak - there is no attempt to seal the seams (you need to read the fine print to find this out). They also charge as much in Sterling as I'm charging in CDN funds. Do the math...

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