I think these rockets are of clay/sawdust construction.
The burn chamber is cast as a cylinder. The feed is cast as a three walled open top box.
We often see rockets built for greater and greater efficiency.
These builders are pretty satisfied with the efficiency so they concentrate on new applications and ease of manufacture.
These simple L rockets put out enough heat to fire clay products.
If "our " rockets with their "high tech" materials are even better, building a kiln that can fire clay objects should be easy.
I especially like the way they fire the combustion chambers in a kiln powered by a perhaps un-fired combustion chamber. Bootstrapping indeed.
I am building a rocket oven, and I am hoping that it will be able to fire ceramics, and even make charcoal.
The difference between the heat needed for an oven and the heat beeded for a kiln is so vast that I doubt they would be practical to interchange. An oven can be heated in a couple of hours and coast; A kiln needs another thousand degrees of heat and must be constantly pushed for hours as the walls and draft are constant drains on the system. Every hundred degree rise in temperature is significantly harder than the previous hundred degrees.
That said, a well built rocket-fired kiln is certainly reasonable. You will have much better results if you already have experience firing kilns and building conventional modern ones. Also, it is not something that can be tested at small scale. The effects of scale are way more significant than in a J-tube rocket mass heater; without a large enough system it is simply impossible to reach certain temperatures. It's like trying to make a 4" J-tube power 50' of mass bench and draft well.
Having built well over a dozen iterations of small-scale replicas of English medieval kilns over the years, and gotten some very hard and beautiful results from the best of these, I would like to do a non-historical build using rocket burners to see how tricky it is to get much hotter temperatures. I think the most difficult part will be the "candling", or very slow fire for the first couple of hours, to drive residual water out of the pottery. Too fast a rise here will cause some of the pots to explode as the water inside flashes to steam and expands, damaging many surrounding pieces as well. Insulation will be critical to keep the whole ware chamber from leaking heat
In response to earlier comments about digging a pit kiln, yes, it really is tricky to do well. Even with the basic configuration perfected, slight differences in proportion and size can make the difference between getting to cone 010 and cone 1. For non-potters, this is a range of soft fragile earthenware that will barely not melt in water, to pots that ring like a bell and will almost be impervious to water without glaze.
As someone who fires kilns daily I want to add my two cents regarding the safety factor. When you're firing clay, you're getting into temperature ranges that can bring heavy metals that are naturally occurring to a level of bio-availability. Its all well and good to get the satisfaction of digging your own clay and firing it in whatever iteration of a kiln you come up with(pit fire, brick kiln, woodfired pit etc). But I will warn you though that you do so at your own risk. If you under-fire some bodies, they'll leach into your food and do damage to your endocrine system. If you eat off a surface that isn't glazed (or is glazed but the glaze is full of lead or cadmium) but seems vitrified, without an appropriate leech test, you'll never know what you're putting in your body. I see potters selling 'dinnerware' all the time that isn't safe and shouldn't be sold for that purpose. Hell, I see Pier 1 doing it all the time! This is not an area that you should ever consider imposing a safety risk on others. Just wanted to air that. I love the notion of all of this experimenting but remember not to share your risk with friends, family or strangers without appropriate testing. We have appropriate technology so that we don't have to take risks as much as our forefathers, I personally use them where necessary.
yes i wanted to add that before but....ooo idk...i decided i had said enough, and truthfully if i feel called to be the voice of reason, i get a bit worried for us =P
but anyway nothing thats fired in a pit kiln, or especially open bonfire, is close to being "food safe". it is not just illegal, it is unwise and dangerous to eat or drink from very low "low fire" pots.
it may be romantic to think of these old school methods, it may be awesome to experiment with them for beautiful non functional objects, but this is not the way to go with any practical food use pottery.
i really enjoyed those links miles posted, i did a lot of reading there. there was a lot about pit firing...apparently most people bisque fire them in a regular kiln before pit firing, which makes a lot of sense....
So, I asked my wife (professor of geology) about heavy metals in naturally occurring clay beds. She says that is a possibility in a stagnant trough, but it is very unlikely to be the case in a hand dug pit, since the heavier particles will subside in the alteration process and hand-dug clay is from the very surface of the deposit. She has full access to XRD and XRF machines, but she said there was no worries about the micaceous clay bean pot that we have eaten from about once a week for the last decade.
I would like to thank those that want to...warn us against...the many dangers that can be found in the art of ceramics...most being in the glazes used (like lead..not the clay itself) and silica dust that can accumulate in and around pottery work. Like stone carving, woodworking, and related...dust can really be a chronic health hazard...
I also strongly recommend that folks read, research and understand all aspects of a project they may try to undertake...including potential hazards...like the real toxicology of ceramics, off gassing from the firing process, and the myriad of other "possible" hazards that can take place...
So by all means if anyone has "case studies," "cited research in the journals of ceramic arts," or related literature covering the subject of...Traditional Firing Methods...and their hazards. Please do post them so we can all read them.
No one here would like to see anyone become ill from exposure to unsafe materials or modalities, or by other means. Yet...at the same time...as I believe Bill B. is trying to illustrate, there is a great deal of "misleading information" and hyperbole about clays, and traditional methods (open firing) that is often spread by those that have little to no experience with it or ever conducting it...
So, I must ask...
If anyone has literature to share...please do.
Actually experienced collecting natural clays and processing them...Then firing them that have presented as toxic in some way...please share that also...
So far in my experience doing this type of work over the decades I have only found:
Dust to be a really big issue....
Many glazes to be highly toxic....especially if low fired...
Low firing and no bisque firing (please note that many so called "primitive" firing methods DO INVOLVE a double fire and not ever in a kiln)...potentially and maybe...leading to the release of possible contaminants in some clay bodies from Mexico, Nigeria, and China, yet this appears to be from "additives" not naturally occurring. My experience additional has seen this only with clays with those types of additives, or commercially deep mined clays from some areas... and not from naturally occurring sources.
One does need to understand the clay if going to store or prepare food!!!
If anyone has more information that we can read on this please share it...
yes it does seem to be that people are generally too uptight about safety precautions in general, and quite likely go way too far in the name of safety.
but i think there is good reason to be with low fire ceramics for food.
that may be because if you take pottery classes they really drill this into your head...so i cant help but have a bit of a knee jerk reaction to the idea. but this is not just a few people who say this, it is commonly accepted "good practice" belief within potters, and really impressed upon students.
heres some of the issue which is not just about the clay or the glaze.
a cup or bowl which is low fired, or even closer to a high fire but not quite up to top temperature, if it does not completely vitrify there are miniscule holes. it will look completely sealed and solid, but there are still small pores. tiny pieces of food can get into to these tiny pores and not be cleaned with a regular (or even totally thorough) clean, so the small particles can build up in there, foster bacteria and other bad funky stuff, and then when used later contaminate food.
this is at least how it was explained to me, and probably all other students of pottery who take ceramics classes.
putting it on a stove and heating it up may help with this, but it is contrary to what is commonly accepted "best practice", especially if someone aspires to be a professional potter and actually sell their wares for use with food. if you do make low fire, pit fire, or raku type pottery, for sale to strangers, it is usually written on a card that it is NOT intended for food use....for liability issues, and letting people know....
I agree that many commercially sold low fire pottery wares are something to be cautions of...with most being downright unsafe!
I have not, as suggested, ever heard in class with other ceramics folks nor experienced anyone from these group (with experience in them) saying that low fire pottery was unsafe for food...IF...that is what it was designed for and the proper clays and modalities of fabrication had been employed when fabricating it.
I would really like to keep the conversation of this post topic aimed at...Positive Feedback... and related stories about...direct experiences... in working with hand collected clays and open firing...not hearsay...if possible.
By all means if someone has...direct experience and knowledge working with these methods...and found a procedural error or means in this discussion that was unsafe when they did it...we should discuss that as well...
So far I, Bill, et al have shared our...positive experiences... with this. I have, because of this post...reached out to other professional potters with direct experience working with hand dug clay and open firing for any warnings they may have to share...No replies as of yet...
I agree that many commercially sold low fire pottery wares are something to be cautions of...with most being downright unsafe!
yeah making art is sketchy, the glazes and the chemicals and doing all sorts of unsafe stuff!
perhaps its a good thing most artists are at least a little bit crazy =P
the worst part of this potential toxic element of pottery is with the weird glazes people use. without using toxic glazes thats a different thing.
but theres better glazes without much weirdness, and if you get them to the right temperature will seal off the clay and then make it not pourous.
sometimes you see a lot of bowls that are raw on the outside, and just glazed with a simple glaze on the inside, i like that style. thats up to standards of "food safe" pottery, while still having the raw and simple look. using the non toxic glazes available and being careful to get it to its maximum temperature.
i am inclined to think that with the right clay and a capable person knowing what they are doing this raw unglazed clay MIGHT be ok food use...but they would have to be very precise about getting to the exact right temperature with their specific clay.
like i said i am not really good at being the voice of reason, i'm much more crazy ideas girl, and count on the more grounded people around me =)
but perhaps the ideas about "food safe" pottery are erring too much on the side of overly cautious.
so here i will borrow some voices from internetsland.....some relevant notes....actually this is linked up to the link on the last page, some very interesting reading and artists pages there...
"I suppose you could use some kind of plastic sealer, but not in order to use
the piece as functional ware. Pit-fired and bonfired wares are not for
food-service use. In the cultures where they use unglazed pottery, the
children grow up with resistance to the bacteria that grow in the clay. If
you or me prepared and ate food out of unglazed pitfired wares, we'd likely
experience intense gastrointestinal distress. Best to just accept that
pitfired and bonfired wares are decorative and non-functional, and make
glazed wares to drink your coffee. "
"Because the pit fire is low fire the pieces are not food safe but
enjoyed for their beauty."
"I wouldn't have coffee out of any pot! ptooy. Now if you had asked
would I try Dr Pepper out of a pit fired pot I would have said, "No,
it a waste of perfectly good Dr Pepper." The only function of pit
fired pots fired here in NA is the function of looking really cool.
The bodies I use in the pit are nowhere near fused enough to contain
water without leaking. Also, when I've fired pots with copper
sulfate, copper carbonate, miracle grow, etc. I don't want to lick the
pots afterwards no matter how yummy they look."
"Please do not
take offense, Earl, but I think that trying to seal a pitfired piece to make
it hygenic is a ridiculous idea. "Modern times" has nothing to do with it.
There are appropriate methods for making utilitarian pottery, and pit firing
certainly is not one of them. Everything about the pit firing process makes
it inappropriate for functional pots. "
"> Maybe I'm missing something here, but isn't pit firing exactly how we got
> our first functional wares in history? I'm not trying to be a smartass or
> anything, but surely I'm missing something here."
Well, no, they were bonfired rather than pitfired. And as I clearly
explained in a previous Clayart post, in our culture we do not have
resistance to the bacteria that grow in porous clay, and thus would
experience severe intestinal distress if attacked by those bacteria. You
have to grow up from birth with those bacteria in order to develop such
resistance, and in those cultures, the resistance may even be inherited.
The idea of sealing pitfired wares in order to use them as utilitarian pots
seems incredibly impractical and inappropriate. I am surprised that anyone
would even consider it."
Bonnie Staffel on thu 6 apr 06
Back in my early days of making pottery, there was a sealing remedy for
teapots where the glaze had crazed.. The premise was that the tea
would seal the pores, and that one never washed a teapot in soapy water,
let the tannin (?) build up inside the pot. Another remedy that was
used was to soak the pot in milk. I did not like the latter remedy as
you got the "pantry" odor to your dishes from the soured milk residue in
pores. It might be interesting to test using strong tea as a sealant.
However, there might be a stain left from the tea.
"I'm selling some saggar pit-fired pots for the first time, and i want to
make a card for each pot, on care & use. But every time I write the
contents, it's full of don'ts, can'ts & not's. Pretty negative. Can anyone
suggest some positive wording for this?"
I am not sure that you can complete eliminate the negative warnings, because
they are necessary. I think that the best explanation statements in such
situations start out by emphasizing the positive qualities of the work. I
would include a brief explanation of the process and then a statement
pointing out the nature of celebratory ritual in the bonfire, pit, or sagger
firing, and the importance of the finished ware as the record of that
I have a statement like that in my "Intro to Clay" syllabus in
reference to the blackware bonfiring that we do. My statement goes like
this: "The bonfiring process has the quality of celebratory ritual, and the
wares have an evocative beauty that speaks of the firing process, but
bonfired wares are more fragile and porous than those fired in other
processes, and cannot be used to contain food or liquids."
<usage throughout the world, and contemporary pottery usage in many tribal and
Third-World cultures. But it is important to point out that there are
significant health concerns to be considered here. In cultures which use
unglazed, porous pottery for daily cooking and eating, children grow up
exposed to the bacteria which live in the porous clay, and develop strong
I think the last sentence should read, "children that survive grow up ..."
Otherwise I agree with Vince's point. The user that a studio potter faces in
the US is uneducated in the use and appreciation of highfired, non-Walmart
ceramics. These same people are Wildly uneducated about the use of pitfired
ceramics as functional vessels. To call a pot functional assumes the
potential user understands what that functionality is. For example, if a user
expects a pot to survive stovetop use, exposed to flame, then no stoneware
object is functional. The question of functionality assumes that the maker
and the user have an understanding of the limits of meaning of that word"
A pit firing is one of the most universal, primitive firings executed today. Firings of this type were an adaptation to firing the ware in bon fires. At some point it was discovered that digging a pit in the ground and firing the ware in a pit led to higher temperatures resulting in a more hard, enduring fired clay. As time continued pit firing evolved to digging holes in the mountainside, a primitive version of today's Anagama. "
It's a shame that we white folk have so many fears. Fear of bacteria is huge, which is silly if you understand that there are 10x the bacterium cells in your body than human cells.
I think the people on this site understand that the bioflora that we are surrounded by at all times is not harmful, but necessary for good health. The 10 year old coffee mug in the picture probably has lots of bacteria on it's surface, but then again so do I.
Owl Peak pottery studio has served thousands of meals to non-indigenous people, all cooked in unglazed low,low fired pottery. I don't know of a single case where there was a problem with bacterial infections from this pottery.
I finally found those photos of my daughter and I firing pottery in a barbecue grill with some scrap wood. She was 7 at the time.
Thanks Bill...you just made me really laugh...and that is a beautiful coffee mug...
My Son's biology teacher just asked that question of his class..."What percentage of "you" is actually "you?"
The majority of the class was "freaked out" that most of what makes them...well..."them" is actually an entire biome of other living things that we could not exist without...and it reminds me of a textbook I had to read (and enjoyed) in college... "Big fleas have little fleas; or, Who's who among the protozoa."We are what we eat...and eats us... Without that balance (which many are lacking and their health suffers for it) we do not have the health we should or could...Thank goodness for the many that are studying fermentation and related autoimmune related topics that have realized this and kept those skill sets alive as well...Much of the firmination (like 400 year old Kimchi) is kept and grown in lower fired earthenware.
Important point you make is that humans have been (with proper means, methods and materials) firing at low temperatures for thousands and thousands of years without ill effect, and I wager will continue to do so thanks to those keeping these skill sets alive...
"I really appreciate the heads up on the potential toxicity!
Any traditional glazes that would address this issue?"
Traditional glazes that I know of (from European sources) are all fundamentally lead melted onto the surface of the pot. Lead ores or carbonates were prepared in various ways and sprinkled or dipped onto the surface and fired; this easily made a beautiful glossy finish. About all modern lowfire glazes involve numerous chemicals trying to reproduce the effects naturally given by lead, and none really do it right. There are many beautiful ones, but they don't have the same qualities as ancient lead glazes.
Highfired glazes, on the other hand, can be very simple in composition, and there are even some natural clays that turn to glaze at the right temperatures.
I have been looking into this more, and found a guy doing traditional ground hog fired pottery, with an ash glaze. The ash glaze is very interesting, being very simple it lends itself to homestead use and is still used to create functional pottery to this day.
I was watching Secrets of the Castle too and it took me back to high school pottery. I've spent some time googling home made treadle or hand powered wheels and the best I've seen is a car wheel pottery wheel (which I intend to have a go making ) but I've been wondering about firing.
I've not yet made a rocket stove although I totally admire them and have plans to make one but I wondered if you could make a small rocket kiln.
My thoughts so far... Where the burn chamber goes up into the combustion chamber, could you attach shelves to the vertical riser and have the combustion chamber drum insulated (a bigger drum with a smaller one inside and ash insulation or something around it). Where the drum joins to the rest of the stove, this could be sealed with ash paste or wet clay so as to make an airtight seal for firing.
To access the shelves it would likely need 2 people (or more) to lift the drum(s) off and on. Would the combustion chamber get hot enough? Would it get too hot too fast or could that be managed by small burns then waiting before lighting again? Any other thoughts?
If it worked it would be a lot more efficient on fuel than a conventional wood fired kiln I would think and I wonder if the combustion chamber vortex would create some interesting patterns or if the total burn of carbon would mean no patterning or something else. Most curious now.
Can anyone more familiar with rocket stoves tell me if they think the concept might work? Not sure if ever I will get to making it (3 kids, 2 high needs, under 7 and homeschooling) but I'd love to try.
Hi folks. I was asked to weigh in on this thread a while back so I apologize for the delay but the wide range of topics required some sort of organizing my response. As I see it there seem to be several concerns and I think that I’ll address them in increasing complexity so ya’ll can bail out when I start sounding like a martian.
So first off ceramics is a field that has a fairly high capital outlay and embodied energy cost, which is fine if this is your business but maybe not quite as practical for a project or two. Add this to the rather specialized skillsets needed to make pots or tiles and you’re probably better off getting them elsewhere for a better ROI (most novices find it hard enough to make something over three inches and keep it roundish). That being said anyone interested in ceramics should give it a go but just be aware that you may be more in the having fun category and it probably will cost more than you could ever save, but if you have fun it’s not my place to say how you spend your money.
As for the durability of wares in low fire… they just aren’t and quite frankly anyone who thinks something fired at 1300 F is vitreous either doesn’t know the what vitrification is or is full of shit.
There are three ranges (broadly speaking) that we fire to: low, medium, and high fire. Vitrification is directly related to body maturity and therefore absorption rates, earthenware will have 5-15% absorption, stonewares 0.5-1.5% and porcelains less than 0.5%. As you fire hotter you get more vitrification. This isn’t to say that there isn’t a long tradition of cooking in low fired wares, cooking a pot does the same thing as cooking food… It kills germs. However those germs won’t stay above the critical 140 degrees for long enough on wares one eats off.
That brings us to testing standards. Unless someone can show you the documentation for acid and alkali(ne) leach testing of lead and cadmium don’t use the piece for food or drink. This testing should be at the cone it’s typically fired to as well as one cone up and down to ensure safety within a margin of temperature fluctuation. Technically there are ppm standards for both of these materials, however both will bioaccumulate as the body has difficulty dealing with inorganic compounds that aren’t needed. Crazing is the crackling pattern seen on some wares… It should be avoided on any food contact surface that is not on vitreous clay as the cracks go all the way to the clay body and if it is porous it will absorb material.
Microwave safety is mostly subjective with the exception of metallic lustre type finishes, depending on the user's tolerance for heat. Once again performance in regard to the heat transferred to a mug handle will improve (less heat felt in grabbing handle) as vitrification increases with higher firings. Use a potholder and you’ll likely have no problem here.
Few potters indeed, actually test their wares but most will tell you that it’s microwave and food safe, combine this with a tendency of potters to use glaze recipes they have found without knowing how to test or correct for faults and you have a tricky ricky situation.
In practical terms, anyone with enough interest can take up and do just about anything to a certain skill level. But there will always be an associated cost to learning.
Thanks James, that was some of the talking points I wanted to get here from a "professional potter." If you have an experience or can speak to any more info on "low fire" earthenware, and/or "Mica Clay" cookware, I am sure all would love to read your views on the subject...
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