Wednesday, February 11, 2009

Tools and Measures (and legondary tales)

Part of an ongoing conversation with Todd, a new member of Early Iron. Todd is getting ready for his first smelt this weekend coming...

Do I need to make a giant scoop to load the charcoal and ore, one with a long handle to keep my hands out of the flue gases or can I just dump it from a bucket or big tin can.

Funny story in this too.

One of the things that is real helpful is to have some standard measures (containers). That way you don't have to actually weigh everything all the time. Your standard galvanized pail holds just a bit more than - four pounds charcoal. This is why you see both my and Lee's records all built around that unit, plus the relationship to the ideal burn rate of about 8 minutes per bucket. You can certainly add the charcoal right out of the bucket held in your gloved hands.

For ore, our original method, learned from Lee & Skip, was using units of one pound. On smelt day, they would scrounge around for something about the right size, weigh out a one pound measure and mark the container. Sometimes lead to things like 'Quick - finish that beer, I need the can to measure ore.' As I remember it, at Smeltfest in 2005, Lee was using a plastic beer cup, marked to about 3/4 full, as the ore measure. Wearing gantlets (of course) he was just putting his hand over the top of the furnace and sprinkling ore out of the cup. Well, he either was moving too slow or hand his hand too close - and the cup melted right apart in his hand! For Early Iron 2, later that year, Mike had made up some quick flat little shovels on long wooden handles. the Boys still use some odd can or cup for the measure, but now empty the measure on to the shovel for placement over the furnace.

Up here, I have a standard scoop, a long handled dish that was originally made as a ladle for pewter casting. It holds (by happy accident) roughly one pound (450 gm) of the Virginia Rock ore. Our big problem is that the group here have become the Ore Kings, we have no local natural supply and have to scrounge all sorts of ore types. The good news is that because of this, we have developed more experience handling differing ore types than perhaps any other team (I've worked with 11 different ore bodies!). Bad news is that each one has a different density. What we used to do is just measure by scoop, and then weigh out a sample scoop and multiply. I find trying to run math in your head during a smelt a real pain. So these days, we measure ore charges on a scale into coffee cans. Then use the long handled scoop to sprinkle the specific charge on the smelter. I normally work with a team of three, one person takes the records and weighs the ore. Remember that your charges most likely will vary in total weight over the course of a smelt as well.

Any way you look at it, you will want long sleeves and leather gauntlets. Not only does the intensely hot smelter have essentially invisible flames, but there will be sparks flying out the top too. Safety glasses are absolutely required - a full face shield is sometimes called for. Expect beard and hair to toast off otherwise. Setting clothes on fire happens often enough that its a smelter's joke (see the Quad State video clip on YouTube).

Now when I started trying to write up my experiments, I realized that there was a real mix of metric and Imperial (even American units!). Since the archaeological reports use metric, I converted all my measures from old experiments over to litres and kilos (and started new records in those units) Of course this takes a bit of a brain strain, from decades in the blacksmith's shop (which even in Europe are mostly still hand measurements or Imperial). Temperature is mainly assessed by eye by colour, then to F, converted to C - as the classic example.
Anyway, we very quickly found that charcoal can change its weight by volume considerably. The variable is the amount of water contained. Now drier charcoal actually burns more efficiently, making for hotter furnaces. If you were measuring by weight alone, you would have the paradox of identical volumes getting heavier as temperatures dropped (What? I used MORE and got LESS ???). So the key here is to use a standard volume. You may see some of my records list litres (volume). That standard pail contains roughly 9 litres (2 1/2 gallons US??)

Any other tools you wouldn't do it without? I did see the the "thumper" in several pictures?

This last piece is copied straight from my 2006 paper 'Adventures in Early Iron ' . You might also want to take a look at the photographs by Neil Peterson (on the DARC iron site)

A number of specific tools have been created to suit specific tasks required over the course of the smelt. Several must have much of their length composed of forged iron (modern steel substituted). These are described here in the chance some artifact samples might exist. This is not considered likely however. The simple contours and long straight lines would make individual pieces ideal for reforging into other objects once they were no longer required for their initial purposes. Some likely dimensions are suggested, bearing in mind the physical requirements of the tasks and the structural limitations of bloomery iron as the material. The metal working ends of these tools would have been fitted to wooden handle. The most likely method would be to use a right angled tab that fit into a slot cut into a square cut handle, the shaft held in place with a simple ring collar. Ideal completed lengths are in the range of 150 - 180 cm. (The versions created for the experiments used cylindrical sockets fitted to dowels or poles.)

Probe ('Radner') - Typically a straight length of 1/2 to 5/8 inch ( in period iron likely 1.5 cm) square stock, with a shaft length at least the distance from top of the smelter to the base (about 60 cm). The tip is forged to blunt straight chisel shape. This tool used for removing blockages to the tuyere (by inserting down the tube). Most importantly used for creating holes in the slag bowl during tapping, cutting the slag mass and freeing the bloom from the smelter walls during extraction. It has also proved valuable to have an all metal version, which allows for hammering on the base end when more force is required.

Bloom Hook - Similar in size to the probe, the end is flattened and forged over the edge of the anvil to create a short hook shape (see illustration). This hook should be roughly 1.5 to 2 cm, a measurement which is critical. Too large, and the hook end will not fit between the smelter wall and the bloom. Too little and it will not get enough purchase on the bloom to exert much upward force.

Rake - This tool can use slightly lighter bar, and the metal end needs only be as long as the diameter of the smelter (about 30 - 40 cm). The tip is flattened for about 6 - 8 cm and bent at a right angle to the shaft. It is used to rake out material at the base of the slag bowl during tapping and any attempt to lower this mass. Also very useful when controlling the physical flow of molten slag when tapping.

Bloom Tongs - These are a specially created set of tongs used for lifting and holding the bloom. The bloom may be as wide as 15 or 20 cm when first extracted, and the jaws of the bloom tongs must be designed to securely hold a wide range of material sizes. These need to have extra long handles to provide gripping strength (and to keep the user back from the intense heat!). (Note that the blacksmith's tongs from Norse finds are simply too small for this task.)

Slack Tub - although not a smelt specific tool, the presence of a water tub within arms distance of the working smelter is essential. All of the tools above will require cooling frequently. In contact with the extreme heat at the interior of the smelter, it takes as little as one minute to heat the working end of a tool to an orange heat requiring cooling. Multiple use smelters might show the circular impression of the coopered wooden tub.

'Thumper' - This is the only all wooden tool used, suggested by a tool illustrated by Boonstra, van de Manakker & van Dijk ( *15 * ). It is a piece of green timber, ideally hard wood (for its weight). A good working length has proven to be about 1 metre, with a diameter of roughly 10 cm. The tool is easier to use if it is fitted with a pair of smaller wooden handles that run parallel to the long axis. This allows the operator to stand above the smelter and lift the tool up and drive it straight down, increasing both accuracy of aim and power of stroke. The working end is soaked in the slack tub before use. (As this tool is basically a length of fire wood, the chances of ever recovering one are extremely unlikely!)

Charcoal Scoop - This tool would have roughly the same shaft length as the probe, but would end in a small D shaped scoop of heavy sheet iron, set at roughly 90 degrees to the shaft. A scoop of roughly 10 cm wide by about 6 deep has been found most useful. Ideally the back curve should be dished up with the front straight edge flat. This tool is only likely to be present if the top extraction method is employed (as described below)


To that list add hammers (both medium and heavy hand hammers and various sledges for compacting). You will find it helpful to have an assortment of oversize tongs, ranging from say three down to one inch jaws (for holding the bloom as it is compacted). A four or five foot length of 1/ 2 round rod is real handy for both clearing the tuyere and also for probing down the inside of the smelter.

Face it, you will spend a LOT of time running back into the shop for that pair of wire cutters, extra pair of gloves, lost pen....

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

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