Bloomery Smelting - Variations on ... Everything!

Jur de Stoute said :

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When you are working with the hand bellows there is another variable coming into play and that is weight of ore charge. About 250-500 grams/charge works about best. If you charge more/charge pumpinng will be ALOT harder, because it chockes the column more. Just drop on the weight per charge and after a while things start to work just fine again.

My usual is to distribute the ore as evenly as possible through each addition of a 'standard bucket' of charcoal.

DD 2 ore analog with the 'standard scoop' - Vinland 1, May 2009

The tool we use for the ore additions is shown in the image above. It holds a bit more material than you could hold in a single cupped hand.

One of the problems we all face in these kind of conversations is that I'm sure our experiences all roughly match - but we are all using slightly different measurements. Both in terms of tools and how we keep track / records.  This goes back to the thing I mentioned about 'kg charcoal per hour' being one thing most of us can record (or calculate from our methods).

On charcoal, we have a 'standard galvenized bucket' sold through hardware stores all over N. America.

Dave Cox adding charcoal in our 'standard bucket' - June 2006

Now, the charcoal does vary in density based on wood species. The most commonly used types here in N A are oak, hickory or maple (or some combination). There is some research to be considered here (??)
The charcoal does also vary in weight per volume due to how dry it is. When my team noticed this, we started trying to measure the weight of our 'standard bucket' at each smelt. The variation is easily 10 - 15%.
Of course another wrinkle there is that we certainly do not weigh each individual bucket, and there is certain to be variations in how full any given bucket might be. On a guess - another 5 - 10 % at least.

On the ore, we originally just counted 'scoops'. We would measure and weight three, take that average, then multiply number of scoops against that calculated weight to get our ore total.
We again realized there was considerable variation there. Now we measure out the ore by full kg (or 500 gm multiples) into cans, then use the cans into the scoop to make it easier to add to the top of the furnace.

The density of the specific ore types we use can vary considerably. The same 'scoop ful' can vary from the DD analogs in the range of 275 - 300 gm - to as much as 600 + gm when the ore type is taconite or hematite grit.

The stack height of the furnace will come into play here too. As the charcoal burns, individual pieces will turn, tumble, and change size. This all will result in the ore particles all falling at slightly different rates. In effect they should start to distribute themselves fairly evenly though the entire volume.
The size of the particles, and the relationship between ore size and charcoal size, will certainly effect this as well.


That being said - I think you may be on to something Jur!
We are always careful to spread the ore in a given charge as equally as possible through an individual charcoal addition. So we never lay all the ore as a single 'slug'. (And yes, many earlier published illustrations suggest this as the method, which I do agree is NOT the correct way to proceed!)
We very rarely charge more than 3 kg of ore into a single charcoal measure (for us the average 'bucket' is about 1800 gm). In method, we would be splitting that ore amount into four roughly equal applications, covering each with a 1/4 bucket of the charcoal.  More typical is charging at 2 kg to one bucket (so roughly 1 to 1)

One consideration on that advise may be the surface area of the furnace as well. I think we all can see that 500 gms ore over a 20 cm diameter results in more of a 'plug' than with a 30 cm furnace. (Our standard here is between 25 - 30 cm interior diameter at the top.)

I think this all just re-enforces what Mark said : Bloomery Smelting is an ART.

Something for those not familiar with historic artifacts:
It is common to find a number of slightly different furnace layouts at a larger 'industrial' ancient iron smelting sites. Usually showing signs of a single firing only. Then there will be one version built over and over again. Obviously the ancient masters would take their generalized knowledge of the iron smelting process, then tweak the furnace design to account for the local clay, ore type, maybe even the charcoal available. Once an 'ideal' combination of design and method was determined - they just repeated that combination over and over.

We do all need to remember that this same problem of matching our furnace and method to our individual local ore does confront us all!

(again taken from a post to Don Fogg's Bladesmith Forum )

2013 Courses in Metalsmithing

This follows from the Event Schedule mentioned yesterday...

Note that there are a number of new programs, and modification on dates from past years.

Start your 2013 forging experience on the right path with weekend programs which will introduce you to the correct working methods, the tools needed - and teach you a good selection of basic techniques.

For the  starting portal go to :  Information on Courses



Basic Blacksmithing April 20 / 21 / 22
June 14 / 15 / 16
July 13 / 14 / 15
September 13 / 14 / 15
Friday evening, all day Saturday & Sunday
This is an 18 hour program that stresses a hands on approach, with a Friday evening lecture and two full working days in the forge. Only 4 students per session, each with their own work station, means close personal attention. Projects include poker, tongs, punches and one small decorative item. Course fee of $325 (+HST) includes coffee and materials. For further details go to Basic Blacksmithing

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Intermediate Level Courses

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Basic Bladesmithing
June 1 & 2

All day Saturday & Sunday
This two day, 16 hour session will introduce the student to the basic techniques required to produce simple hand forged knives. Covers: historic patterns, alloys, heat treating, forging shapes, basic finishing & hilting. Each student will forge and work to finish a small belt knife, plus rough forge a number of basic blade shapes. Requires 'basic' level experience, please ask for details. Course fee of $325 (+HST) includes coffee and materials. Session limited to four students.


For more details on this special program - go to Bladesmithing Course.

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Intermediate Blacksmithing
November 9 & 10
All day Saturday & Sunday.
This two day, 16 hour session will cover forge welding, punch work (flat and sculptural), tool making, and design for the Smith. Requires basic level experience, please ask for details. Course of fee of $325 (+ HST) includes coffee and materials. Session limited to four students.


For more details on this special program - go to Intermediate Course.

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Working Structual Steels
September 28 & 29
All day Saturday & Sunday This two day, 16 hour session will cover the basics of working with structural steels : PIPE / ANGLE / CHANNEL and more. The program will cover specialized tools, basic work with the air hammer, as well as design considerations. Requires a minimum of basic level experience, ideally intermediate level, please ask for details. Course of fee of $350 (+ HST) includes coffee and materials. Session limited to four students.


For more details on this special program - go to Structural Course.

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Introduction to Layered Steels
July 27 & 28
All day Saturday & Sunday
This two day, 16 hour session will introduce the student to the basic techniques required in the creation of layered steels. Covers: alloy mixes, basic pattern generation and history. Each student will create a layered billet, plus will forge a small knife from a prepared block (provided). Requires intermediate level experience (ability to forge weld), ideally with basic bladesmithing, please ask for details. Course fee of $375 (+HST) includes coffee and materials. Session limited to four students.


For more details on this special program - go to Layered Steel Course.

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Special Interest Courses

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 Introduction to Smelting Iron May 24 - 26, 2013
(Friday evening, all day Saturday & Sunday)
This course dependent on registrations (requires full class of 4 students due to materials cost)
This two day, 18 (+) hour session will involve the student in the construction and operation of the 'Econo Norse' small scale iron smelter. A Friday evening lecture will cover the theoretical and historical background of smelting iron: ores, furnaces, process, equipment. Saturday will start with the construction of the furnace, plus preparation of charcoal and ore, ending with pre-heating the furnace. The actual process of the smelt on Sunday takes roughly 8 hours. After this, the resulting iron bloom will be extracted from the furnace, and given a primary consolidation. The iron produced will be cut to sections and shared between the participants. This program does not require any previous metalworking experience, and is of interest to students of history as well as blacksmiths. Course fee of $400 (+HST) includes coffee and materials.
For more details on this special program - go to Smelting Course.

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Basics of Metal Casting

February 9 & 10
November 16 & 17
All day Saturday & Sunday This intensive hands on session will introduce the student to two methods of creating small objects using the casting process:
SAND CASTING IN BRONZE : First a master pattern will be caved in wax, then each student will learn how make molds using the green sand process. Several pours will be made.
PEWTER CASTING IN STONE : Each student will carve out a re-usable soapstone mold, then make a number of pours.
The two day, 16 hour course will include a look at historic cast metal objects, plus an overview of the tools and equipment required to set up a small scale workshop for cast metals. No skills requirements. Course fee of $325 (+ HST) includes coffee and all materials.


For more details on this special program - go to Casting Course.

2013 SCHEDULE - Posted!

Public Event Schedule 2013 Latest Update : January 2013 - Dates are tentative NEW courses, demonstration events for 2013, 2013 is an 'Arts' year, many events reflect this. For more details on the specific events, use the links provided. (Note that most event links take you off the Wareham Forge series.) Detailed Information on this year's courses at the Wareham Forge can be found HERE

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2013 Year at a glance
This table shows all of the year's (potential!) activities and will quickly let you see everything on the timetable

"Blooming is an ART" - Ore Particle Size

...again taken from a comment on Don Fogg's Bladesmith Forum

Mark Green on 17 January 2013 

In my usual ore mix, the big pieces are bean size. From that, down to near dust. I think the mix of sizes keeps the flow down healthy.
Back when I used the Spanish red ore, it was very fine, but I'm not sure I knew enough then, to know if it mattered.
I've come to believe it all matters. The size of all the components, to the stack size, to the airflow/volume. But, there are always so many variables with any given smelt, that doing, what has worked well for you in the past, seems to be my best plan these days. Unless I'm experimenting, I stick with what has worked the best, for the ore I'm using that day.

Blooming is an art. There is way to much science going on in the whole process to worry about it. ...>

Mark - I especially agree with your statement "Blooming is an Art".
Beware those that suggest there is a cookbook approach that can be employed. The experienced know there are just way to many variables in play!

Again with the patience of those with more experience reading here...

Lee Sauder has gently reminded me on a number of occasions not to stress 'stack height' too much, because the reality is that it is *hang time* which is important. (Stack height here being the measurement from the top of the tuyere to the top of the furnace.)
As Jur de Stoute had correctly suggested,  for an individual ore body, there is an ideal relationship between particle size and hang time. The reduction chemistry is a gas onto a surface reaction. If you make your ore particles too large (or the ore is too dense and solid), there will be more time required in the working column of the furnace for the desired conversion of iron oxide to metallic iron to take place. The converse of this is that if those particles of metallic iron remain in the carbon rich column for too long, they will absorb excess carbon, and un-desirable *cast iron* will be the product.
The historic purpose of direct bloomery furnaces was to produce an extremely low carbon iron - an easily forgeable metal for general purpose applications. Although many reading here are bladesmiths, you never should forget that truth. As you have seen from the postings of various smelt workers here, it is possible to create a higher carbon metal, suitable for cutting tools. Looking at historic practice however, it is extremely difficult to see if this was ever done intentionally. The evidence appears to point to the use of re-melting hearths being used for carbon/iron alloy production. (Check the other thread : 'Evenstad Experiments')

Back to particle size :
One very important limitation on what people may suggest here : Consider the ore type, quality and source.
We all are generally working with some locally available materials as our ore. Hematite blasting grit (1 - 2 mm of 98% Fe2O3) is going to require a much different furnace arrangement to that needed for working with 'Spanish Red' potter's oxide (powder at 81 % Fe2O3) or ... (insert your own ore type here).

I can tell you from my own experience. My early friendship with Lee and Skip Williams resulted in me often hauling 500 lbs of their (excellent) Limonite rock ore home from Lexington to my base in Central Ontario (roughly 85% FeO). So my 'working' furnace system was designed around the use of a rock based ore, roasted and crushed, with pieces ranging from 1 - 5 mm (rice to pea). Most typically our furnaces had 40 - 45 cm stack height, with air volumes adjusted for an optimal 8 - 10 minutes per 2 kg charcoal **. This produced a 'hang time' of something about 30 minutes *. The end result was typically a nice dense workable iron bloom (when I managed not to screw something else up.) Using the hematite grit in the same furnace set up, the end result was a very crumbly texture, but a medium to high carbon metal. (And yes, small amounts of cast iron was sometimes the result as well.)

Because both Jur and Mark have mentioned this - our standard here, with the more solid ore types (various source limonite rock, industrial taconite) is to aim for 'pea to rice' - and roasted. I have only had a couple of chances to work with primary bog ore (both roasted and not), sizes there more pea to walnut (5 - 25 mm). Although we are using slightly different ways to describe this, I do see we are all working in the same ranges. The only difference I see with what Jur has described is that I normally keep the smaller 'dust' particles included (as normally does Lee, I believe Jesus). I never worry about washing these ores, figuring what sand / rock remains will just give me nice juicy slag, which I can just tap off.


Jur has asked about using the various potter's oxides.
We have used both the 'Spanish Red' and the higher iron concentration (93% Fe3O4) black. The problem with attempting to use these powders 'straight out of the bag' is that the particle size is so fine, the air blast blows almost as much back out of the top of the furnace as you manage to get into the furnace! The solution we developed (our 'DARC Dirt' analogs) is to mix 10% whole wheat flour in with the oxide. Water is added to create a dough, which is then spread on sheets to dry. The resulting 'cookie' is broken up into pieces. The flour acts as a binder, holding the oxide together until it falls into the top of the furnace. This pretty much eliminates the problem of the oxide blowing out of the furnace.

DARC Dirt 2 analog - from black potters oxide (scale inches / cm)

* That is *very* rough - based on estimating the volume of the furnace  X ideal consumption rate.

** I'm gathering data for a paper to be delivered this spring. One of the problems is trying to find some 'universal' measurement that can be used that links back to air systems / volumes (where my interest lies here). It does appear that 'consumption time against charcoal' may be the most commonly recorded measurement.