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Historic Firebrick Recipes?


Case Draughn

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I'm looking for firebrick recipes to make bricks for building furnaces and forges with hopes that the bricks may be reusable. I haven't had much luck in finding what I'm looking for.

 

I'm a historic archaeology grad student and bladesmith, so naturally I've experimented with making clay furnaces. Where I'm living now for school I don't have immediate access to unlimited clay like I used to, so I'm planning on making a trip to get a big pile of it for making bricks and other things, so that I have materials on hand for putting together or moving furnaces. I don't have very much space here either, so I'd like to be able to deconstruct and put away my furnaces when I'm finished with them - another reason for bricks. 

 

Being an archaeology student, I want to make my own bricks for this. Buying modern firebricks surely would be easier and better quality, but it's not fun. An authentic historic recipe would be the coolest. I already know where to dig my own kaolin and stoneware clays and pretty much any sort of temper that might go into ceramics. 

 

What I want to know is what materials and in what proportions for making firebricks for these purposes, and what would be the best method of firing for making these myself?

 

Alternatively, if there's something that would provide a greater advantage to the historic recipe, hit me with it.

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As a fellow historic archaeologist and collector of Southeastern stoneware, I gotta say you're probably on your own. The kiln bricks and kiln furniture I've seen are usually just the local stoneware clay that hasn't been cleaned as much as it was for the actual pottery.  I haven't seen any "recipe" per se for firebrick.  One thing I wouldn't do is add sand. That will tend to melt on the hot face side of the bricks and fuse the bricks together.  Big chunks of quartz are okay, though.  

 

You'll need to make a brick mold, and there are lots of resources for those.  

 

As for firing, the potters tended to either clamp-fire or just build the kiln from green brick and let the first stoneware firing do the job.  In your situation a clamp is not going to be feasible.  Just be sure the green bricks are as dry as they can get before using.  Steam explosions are not fun.  For small batches I'd even bake them in an oven at 400F for a couple hours to ensure they're truly dry before using them in a furnace.  

 

All that said, how large a forge or furnace are you thinking about?  when I've made clay forges and melting hearths they fit on top of a 55-gallon drum lid for portability.  If you're wanting to smelt, bricks are too good at insulating and tend to lower the yield, which is why most people use the kaolin/sand/peat moss blend and let the walls taper in thickness from around 2" at the base to 1/2" at the top.  And the best part is, after running a smelt or two, you can crush the furnace for use as grog in the next one.  If you're gonna go historic, go all out!

 

Speaking of historical, the big stone blast furnaces were lined with either firebrick made from the local stoneware clay or with refractory sandstone blocks.  Either one was expected to last six to nine months of 24/7 smelting.  Puddling furnaces were usually common red brick lined with firebrick, and even then the actual puddling chamber floor was an added layer of blue clay and grog.  Iron slag eats refractories.  

 

Forges, on the other hand, can be pretty much any kind of dirt that sticks together.  The heat escapes upwards and doesn't tend to melt the sides.  

 

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For a forge, I want a sideblast charcoal forge somewhat like a Japanese bladesmith forge, i.e. a rectangular trough with sides made of stacked bricks in a pyramid. I need something for refining blooms and making good forge welds. I want it to be semi permanent. I don't have a proper place for ventilating a coal forge in my workshop, so I'd be keeping it in a partially covered area outside or dismantled and stored.

Otherwise, I see myself using the bricks mostly for hearth steel furnaces or quick small furnaces for melting other metals like copper and bronze in crucibles. Proper smelts I'd most likely be building a tall clay furnace. I want to expose more archaeologists to the actual processes of the creation for the random bits of things we stare at and label in the lab. A quick furnace I can pop up makes it easier. I don't see myself doing a real iron ore smelt any time soon, but recycling bits of iron and steel shouldn't be too difficult.

 

I've built a small clay furnace for melting copper in crucibles, and it works, but I'd rather crush it and reuse the grog. Without much space and time for constructing all sorts of furnaces, I need something more versatile. 

I might try to make a small reusable furnace stack - basically a fireclay coil pot without a bottom. I saw something like it in a video from Officina Ferraria. Just create a sacrificial base and stick the reusable top on with some more clay. 

 

I've read that lots of grog is probably the best temper to use. I've also read about creating insulating air pockets by adding wood dust or charcoal. I heard of lime and ash being used too although I'm not sure what purpose it serves

 

I have a big ol chunk of quartz. Something like a seam. It falls apart into small pieces quite easily. I could add that too, I suppose. 

 

Today, I found a few books talking about firebricks, but they don't really say much except that they're made from fireclay. And coincidentally, one claims the fireclays of Escambia county Florida are the best. 

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Well - this gets tricky....

I approached this from the perspective of making furnaces for melting glass and for heating iron to forging temperatures.

Modern analytical chemistry and industrial-scale purification and manufacture have changed this field absolutely beyond recognition.

Before modern analytical and industrial techniques people threw about colloquial names for the materials they were using without having any knowledge of what impurities were and were not present in the materials. The result was often concoctions which couldn't be reproduced because of the presence or absence of impurities in the materials used. This plagued glass making until recent decades...

My guess is that the only reproducible historical recipes would be ones that state the origin of the materials - I think sometimes industries grew up in particular places because of a local supply of particularly good quality materials.

Another option would be to try small samples from different places and see what does and doesn't perform well before selecting the materials for building a furnace.

Historical patents in English or German (or possibly another language...) might be another source of information - patents were typically required to provide enough information to make the results reproducible - though this varied with jurisdiction.

A lot of concoctions that I see floating about on YouTube are complete nonsense which will fall apart when heated - my guess is that concoctions which were complete nonsense would also have been floating around in the past in spoken and written form - so likely good to test small samples before building anything big...

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That's why I teach other archaeologists to forge nails.  Makes a huge difference in how you look at a site!  I'm all about experimental archaeology and doing things the historic way.  The last person I taught to forge nails I even let 'em use wrought iron for the last one they made so they could really understand the difference.  And you should have seen the comment I left on a report where the author described a bloomery as "a sort of oven for making iron."  I review contract reports as part of my job, and the folks who work in Tennessee have learned they need to do their homework if they're describing any sort of metalwork-related site.

 

Grog is definitely the best temper.  Lime I don't know about, but charcoal works, as does peat moss, ground up horse manure, chopped straw, etc.  I think you'll find the small reusable stack is the best option for small crucible runs of nonferrous stuff.  

 

And yep, good old EPK (Edwards Plastic Kaolin) is mined right there in Florida.  The mine is temporarily closed, apparently, so brand-name EPK is hard to come by these days.  

 

If you haven't read this thread, now's a good time: 

 

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2 hours ago, Will Robertson said:

My guess is that the only reproducible historical recipes would be ones that state the origin of the materials - I think sometimes industries grew up in particular places because of a local supply of particularly good quality materials.

The books I looked through today mention this sort of thing. In the 18th and 19th centuries, plenty of US firebrick manufacturers popped up but then disappeared quickly. As soon as the good clay became too cumbersome to transport, they quit. Meanwhile, British firebricks were constantly being imported.  

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4 hours ago, Alan Longmire said:

That's why I teach other archaeologists to forge nails.  Makes a huge difference in how you look at a site!

This story relates to that and will drive most people on this forum nuts. I'm finishing up a class on lab methods. Basically, we're learning how to identify and process all sorts of artifacts collected from excavations. Even after plenty of reading about the different ways nails were made, many of the students still could not comprehend the differences in wrought, cut, and wire nails other than they look different. Then it was nearly futile to explain in solely written format the differences in use for wrought iron vs. cast iron. I recommended some demonstrations next time the class is taught. 

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When I teach the metals class for historic lab I use stuff from the comparative collection, because it's much easier to explain why early cut nails took so long to catch on.  The machinery and methods of the time (1790-1830-ish) meant the strips of wrought iron for the nail cutting machine were rolled such that the cut is across the grain of the iron, meaning you can't clinch an early cut nail.  They snap off with a flat point.  Not a big deal?  It is when the only way you know to build doors and window shutters is by clinching over the nails.

 

I do the same sort of thing with ceramics.  If you know the how and why of an object and its method of manufacture, you see how it shapes the whole society it's used in.  Throw in the economics and it explains even more.  

 

Open Google Earth and zoom in on St. Austell, Cornwall.  See those massive white craters to the northwest?  That's where the clay for 250 years of refined whitewares for the whole English-speaking world came from.  Also the clay for those firebricks.  It was loaded on ships and sailed around Wales to Liverpool, thence up the Mersey to the inland navigation networks, loaded onto canal boats, and towed up to Stoke-on-trent.  Why there?  That's where the established kilns were already in place, on the canal network imagined in the 1750s by Josiah Wedgwood (among others), at the exact spot where there had been a pottery center for years. The canals nearly removed the cost of transportation, and when steam power arrived they brought the coal directly from the mines to the potteries as well.  The finished pottery (and bricks!) were then shipped back to Liverpool and loaded onto ships as ballast.  The English combination of a huge labor force, low wages, and low transportation costs meant that the United States would not be able to undercut the price of a dinner plate until well into the 1880s.   

 

Same thing with the humble pocketknife.  Made in Sheffield where the steel mills and water power were. American industry couldn't do it at a competitive price until the 1890s.  

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17 hours ago, Case Draughn said:

The books I looked through today mention this sort of thing. In the 18th and 19th centuries, plenty of US firebrick manufacturers popped up but then disappeared quickly. As soon as the good clay became too cumbersome to transport, they quit. Meanwhile, British firebricks were constantly being imported.  


Yup - that rings true.

I just realized today that when I said to hunt for patents in other languages I forgot to give the terminology - Germany had fairly big glass making and steel making industries and some of the terms for different refractory brick are "Schamotte Steine" "Feuerfest Steine" and "Feuerleicht Steine" - Sweden also used to have a big iron and steel industry - it's "Ildfast Stein" in Norwegian so I guess it's the same in Swedish - those might be a help in finding historical records and historical patents in other languages.

Google and Google Patents are great but sometimes the quality and practical usefulness of the results varies enormously depending on the language in which the search is written.

I've seen clay-like material being obtained from the waste water treatment plants at quarries - rainwater carrying silt is passed through sedimentation ponds or tanks where the silt settles and forms a clay-like substance - I guess that knowing what the quarry is quarrying would tell you the chemical composition of this.

When folk who're doing ceramics work with a new material they typically test fire a lot of small pieces to get an idea of how it behaves - there's usefulness in that approach.

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2 hours ago, Alan Longmire said:

Open Google Earth and zoom in on St. Austell, Cornwall.  See those massive white craters to the northwest?  That's where the clay for 250 years of refined whitewares for the whole English-speaking world came from.  Also the clay for those firebricks.  It was loaded on ships and sailed around Wales to Liverpool, thence up the Mersey to the inland navigation networks, loaded onto canal boats, and towed up to Stoke-on-trent.


Thank you very much - that's interesting - I'd always wondered where that refractory brick came from.

When you say "white craters" am I right in guessing that with clays the very rough rule of thumb is that white usually tends to imply pure?

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Up to a point, and then it's all dependent on the source stone.  Stoneware clay and fireclay is hydrated aluminium silicate with some other stuff along for the ride, usually mica, quartz, and other silicate minerals.  Most of it fires up white to buff, but some fires dark brown to deep red, depending on kiln atmosphere.  My favorite clay body for utilitarian stoneware is gleyed clay from the Catawba River valley in Lincoln County, North Carolina. Comes out of the ground a dark blue-gray, and fires to a dark indigo-tinged brown.  The local potters made up an alkaline glaze of wood ashes and glass, which on a light-firing clay gives a lovely celadon green, but due to the presence of rutile (titanium dioxide) in the Lincoln County stuff, fires to a deep green with flecks of sky blue under reduction, or a very dark green in oxidation.  

 

The pure white kaolin and the buffy ball clays are that way because they lack iron or other metallic oxides is all.  Pure by one definition only? If you want to make translucent white porcelain you need kaolin, roasted ground flint (anhydrous silicon dioxide), and feldspar (calcium, sodium, or potassium aluminum silicate) Feldspar is the key to the translucent body and glaze.  That's also how salt glaze on stoneware works.  Throw common salt (sodium chloride) into a kiln at 2200 degrees F, and it vaporizes. The sodium bonds with the silica in the clay to make a sodium silicate glass, the chlorine exits the kiln chimney where it combines with water vapor in the atmosphere to make a mild hydrochloric acid, much to the annoyance of folks downwind.  Still better for you and the environment than a lead glaze on low-fired ceramics... and that is a factor in why clay tablewares are they way they are in the western world today.  

 

While I'm digressing on the nature of clay and the roots of the industrial revolution, if you're at all interested in how it all came together I highly recommend the book "The Lunar Men" by the unfortunately-named Jenny Uglow. Who knew that in 1760 a bunch of scientifically-minded northerners, including James Watt, Josiah Wedgwood, Matthew Bolton, Erasmus Darwin, and Joseph Priestly, decided to meet every full moon to discuss things that caught their attention?  In that one group you have the god of steam power, the father of industrial pottery, the guy who perfected the fully mechanized textile mill, a pioneer of modern medicine (and grandfather of that Charles Darwin guy), and a father of modern chemistry. All feeding off each others' energy.  Without any one of them the British empire as we know it may have never come to pass.  One can debate the merits of that, of course, but the modern world would be a very different place without them.  

 

Sorry, I'll disengage Lecture Mode, y'all didn't sign up for a class! But that's Historic Archaeology (Post-Medieval Archaeology in the UK and EU) for you. Everything affects everything else when long-distance trade of bulk materials becomes possible.

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All my clay knowledge has come from my pottery making. Early on I read every Ceramics Monthly I could get my hands on. At the time I was working in a university library, so.... they had a lot of them! I found and collected several good articles on prospecting and processing wild clay from CM. My plan was to find my own clays and make my own clay bodies. Never really got the time and Central Texas is not known for it's plastic clay deposits. Once I realized that folks already mine that stuff, crush it, sift it, and bag it up for you, I figured I'd just buy my ingredients.

 

A few thoughts: If you're going to make your own brick, you will need to make a kiln for firing them. You can, like Alan suggested, use them green and let the first firing vitrify the bricks, but you will need to go very very slowly and/or have a very open brick body.  Lime in low to medium fired clays will cause lime pops once the lime re-hydrates and expands in the vitrified clay. Other additives won't have that problem. The clay you find will determine if you need to add temper that will improve the temperature performance of your bricks as well as their insulation properties. Should be really fun if you find some good stoneware or fireclays to play around with.

 

You might try finding an index of CM if you want to go hunt your own clay.  When I wanted to understand the dry materials I was using for clay bodies and glazes, I sometimes turned to digitalfire. You might google that site as well.

 

If I can get my hands on my article copies, I'll reply here with the bibliographic information if you're interested, Case.

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2 hours ago, Taylor Hendrix said:

If I can get my hands on my article copies, I'll reply here with the bibliographic information if you're interested, Case.

I won't turn down any useful information. I know a little information about finding and processing wild clay, but the most useful of it comes from YouTube videos. I've read books and articles for a class on archaeological ceramics, but to be honest it wasn't useful at all when it comes to these things. I ended up basing most of my processes for a project on information in videos and blogs from potters in the southwest. At that time, I never did come across a published written source that would accurately describe in enough detail the ways you can find and refine clay. My project was mining clay, refining it, making cooking pots (with appropriate temper), and using the pots until they broke to see how they last. Unfortunately, I had little to no experience in any of it before then, so the project didn't really work out as intended when it came to the form of the pots themselves. I ended up finding a few different clays, but one stood out. I ended up throwing it out because it was just too sandy and difficult to refine. I'll add a picture. Since then, it has occurred to me that it might be naturally clean yet sandy enough to be used as is for smelting furnaces. If anyone can tell from the color and texture let me know. I remember this stuff being dark to light gray with pockets of red-orange. I dug this out of a creek, which explains the sand. I could find more of the same clay but without the sand as big, loose chucks just sitting on the dry creek bed. Only the outside would be covered in sand. I remember trying to wet process it, but it just would not totally dissolve in the water for more than 4 days even after I broke it into smaller pieces. And what I did manage to wet process remained too sandy. Anyway, I talked to one of my archaeology professors who said it looked sandier but similar to the high kaolinite clay that's here in Escambia county, FL. But like Alan said because of the sand, this wouldn't be good for bricks. 

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Here you go, Case. I've got a great report from somewhere titled "Clays of Texas" with loads of great info including details of a home-made pug mill, but I can't find any author or publishing details, but four of my copies had the biographical info intact. The second article in my list would be a great read for you, certainly. I started collecting maps for myself back in the day after reading that article.

 

Levigation with a riffle box is the usual method for removing sand and larger, heavier inclusions in the clay (#3). Sounds to me, though, that your white clay may be a shale or some other cousin of clay. Yes, native kaolins can be quite short even after grinding them fine. Some native clays do take quite a bit of grinding to get them wetted, but your description reminds me of a Texas shale I collected. Even after ball milling, it would not slake like plastic clay. Such are the nature of shales. I'm saving my find for use in a glaze some day.

 

1) Aigner, Mary K. "Clay Prospecting." Ceramics Monthly, Sep 1989, pp. 96-98.

2) Aigner, Mary K. "Geology and Maps for Clay Prospecting." Ceramics Monthly, Apr 1991, pp. 82-83.

3) Petersham, Miska. "Using Natural Clays." Ceramics Monthly, Jun/Jul/Aug, pp. 100-103.

4) Schmitz, Robert. "Technical: Evaluating Clay Bodies." Ceramics Monthly, Dec 1985, pp. 69-73.

 

Be sure to check out other clay periodicals for possible information. The three that I know are Ceramics Monthly, Clay Times, and Pottery Making Illustrated. The first two would be better possibilities as they are more broader in their coverage. PMI is more how to form objects etc.

 

Several book-length treatments of clay have been written as well, so the information is out there to find.

Let us know how things go.

T

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On 12/2/2023 at 7:37 PM, Alan Longmire said:

The local potters made up an alkaline glaze of wood ashes and glass, which on a light-firing clay gives a lovely celadon green, but due to the presence of rutile (titanium dioxide) in the Lincoln County stuff, fires to a deep green with flecks of sky blue under reduction, or a very dark green in oxidation.

 

Yup - wood ash is chemically interesting stuff - the composition varies with species and location - it can be used to give a fairly wide range of colours depending on the chemistry of the glass - I guess that applies to glazes as well.

 

On 12/2/2023 at 7:37 PM, Alan Longmire said:

The pure white kaolin and the buffy ball clays are that way because they lack iron or other metallic oxides is all.

 

Yes - that's my understanding as well - iron oxide acts as a flux and lowers the melting point of the whole thing - leading to the clay effectively beginning to vitrify at higher temperatures.

I'd heard about the fumes from salt glaze - the thought of the damage it could do to my refractory put me off ever trying it!

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In terms of making refractories I've a lot of respect for this guy - unfortunately we don't know the exact chemistry of the clay in the area where he works - in this video we see some of the vitrification problems that can occur at higher temperatures:
 

 

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Depends on the clay and how you want to use them.  Like I said above, for a forge any old bricks are fine as long as they're dry, they're not going to get too hot.  For a melting hearth, these might do fine, they might be too thick and constitute a heat sink. Suitability for a crucible furnace is iffy, depends entirely on the clay and temper.  That little clamp/kiln dude made is pretty spiffy, but you're going to want a crucible furnace to be able to withstand another thousand degrees F hotter.    

 

As an aside, I hadn't checked him out in a couple of years, glad to see he's still at it and getting better.  Also jealous of his bog ore deposits that he calls iron bacteria. We have them here as well, the old maps call them chalybeate springs.  You can see the slime on the surface, and the bright orange bacterial mud-goo that is raw bog iron on the sides and bottom.  I don't know of any near me that are large enough/productive enough to use as an ore source, though.

 

Teacher-y aside #2:  People wonder where iron ore comes from and whether it's volcanic.  It's not.  It's biological or literally meteorological.  Vast beds of bog ore made by bacterial mats fossilized into Goethite/Limonite/brown ore, frequently found atop beds of manganese ore produced by a similar method.  Transported in aqueous solution and sometimes partially metamorphized, you get the hematites/red ores and the carbonate ores (siderite, blackband ore).  Magnetite is the only iron ore of igneous (not volcanic!) origins.  Meteorite iron is the other source.  That in turn came from the remains of stars (iron is the final end product of normal stellar fusion, the heavier elements require a supernova).  Now you know!  Whether or not you care is another story. :lol:

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i have to somewhat disagree on the statement that any kind of brick can work for a forge, i ran a brick forge for about a year, an my findings were: there are some red concrete bricks that quickly disintegrate due to the reversing if the bonds in the concrete, but the true clay bricks do last longer, but do slowly melt and crack apart. they work ok for about 10 uses before they are useless.

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1 hour ago, Kyle Vance said:

i have to somewhat disagree on the statement that any kind of brick can work for a forge, i ran a brick forge for about a year, an my findings were: there are some red concrete bricks that quickly disintegrate due to the reversing if the bonds in the concrete, but the true clay bricks do last longer, but do slowly melt and crack apart. they work ok for about 10 uses before they are useless.

I think he means clay firebricks, not concrete. Concrete doesn't like heat. They will indeed not last very long, which is why usually you line them with a clay mix, which gets replaced/repaired when needed. 

Jeroen Zuiderwijk

Facebook page: https://www.facebook.com/barbarianmetalworking

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I did mean clay bricks, and yes, some ordinary red clay bricks (the high-shale mix ones) will eventually crack and crumble.  Pavers and old solid bricks hold up better for forge use, by which I mean solid fuel open top forge, not enclosed or gas-fired.

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18 hours ago, Jeroen Zuiderwijk said:

I think he means clay firebricks, not concrete. Concrete doesn't like heat. They will indeed not last very long, which is why usually you line them with a clay mix, which gets replaced/repaired when needed. 

I do know that he meant clay, I was just tossing out the fact that there are red bricks that are made of concrete that you must watch out for.

I have found that the clay bricks hold up pretty well against charcoal, but leave something to be desired if you are burning coal

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  • 3 weeks later...

Well, I never did find any suitable clay in Florida. All of it was too few in quantity or too sandy. Since I'm visiting my parents for Christmas, I took the chance to dig some clay here in MS. I was planning on hiking back into a creek in the woods where I found the light gray clay previously, but my dad suggested looking for similar clay at the bottom of the pond there. He said he remembered seeing a nice gray clay when they were digging out the sides to expand the pond a bit. Mississippi has been in a drought, so the pond here is nearly dried up, and you can walk across it pretty deep. We immediately spotted some gray clay sticking out and a few inches down it seemed to be pretty fine, clean gray clay. Practically good enough for making a pot right there. I dug out a bucket full and then tested some other spots. I found about six inches deep a bit further out a striking blue-gray clay. Also extremely fine and clean. Got a bucket full of it too. None of it had any discernable sand content. I'm planning on going back to get more, but I'd like to hear what y'all think about it. I'll include some pictures. 

 

 

 

 

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This has been a very interesting and informative thread! I know very little about the subject, but I have spent some time experimenting with clays. Initially, I wanted to make my own greensand for bronze casting experiments. So I bought some cat litter with baking soda (as it was the purest I could find!). I theorized that the baking soda may cause some casting problems, so I tried to wet purify it. However I had a lot of problems with the clay not settling. So I added some Alum, which sped up the settling, but it still took forever to dry. Finally, I just mixed the screened baking soda clay with the screened sand and tried to cast some bronze. However, the clay somehow allowed the bronze to flow around the sand (the baking soda must have acted as a flux, and the clay must have liquified), and I ended up with a big bronze ingot with sand embedded in it! So much for those experiments! 

 

For Japanese iron patination, the recipe requires iron bearing clay, but this time I just got it from a pottery supply store! It was expensive to ship, but it worked great. I also used some of the clay to try to make a replica of Jomon pottery, but that didn't go very well! In the spring I'm planning to redo the heat treatment on some Japanese blades that have been annealed, but for that I'm buying the clay recommended on this forum. I'm done with my clay experiments!

 

I'd try making a test brick or two out of the clay you have, why not? You can also buy some fire bricks to help test them. I use fire bricks with my forge. They eventually disintegrate, but that's the nature of these. Before I got my commercial copper melting furnace, I made my own furnace out of a bucket with kaowool covered with refractory, and a propane torch used for burning weeds. It got hot enough to melt copper, but it was very slow (higher heat seems to benefit from compression of the propane). I've read others making their own kiln using a similar strategy, and it's pretty easy and cheap to do. But if you want to do it all the old way, you've got to make your own kiln out of clay! I guess you could make a beehive style one, make a small one and test how it works as clay for the kiln, and how good the kiln is at firing test bricks.

 

Lots of options here, but I'll leave the further experimenting to you! Water purifying was fun, but I've yet to find a use for that clay!

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