The biggest MYTH in pottery.

[@slowerpicker]

Implicit in your explanation is this fun chemistry fact: Leatherhard pots that feel abnormally cold are actively drying because the water is taking heat from the clay in order to transition from liquid to gas.

[@PotterytothePeople]

love this !

[@TealCheetah]

In middleschool, I eventually managed to make one nice bowl on the wheel. Someone else's project exploded in the kiln and trashed my bowl. Decades later and Im still upset about this.

[@PotterytothePeople]

a totally valid thing to be upset about! 😫

[@aftersexhighfives]

I have a similar story. My piece is marred and every time I dust it I am reminded and think freaking Sarah. Then turn it back to the pretty side😂

[@granmabern5283]

@@PotterytothePeoplewhat ticks me off is, my prof said it was my piece that blew up and broke everyone’s stuff...yet it was HIM that did the firing over the weekend...

[@jakereiland]

I threw a huge piece with multiple sections in high school and it exploded in the bisque firing (the only piece I’ve ever had do that I believe) and it ruined many other pots. Luckily nobody cared

[@theoriginaltubeofyous]

@@granmabern5283 sounds like regular middle school teacher brain tbh. always the students' fault.

[@joseph96345]

My pottery instructor was adamant about explosions being a result of moisture and not air. It just makes sense. Water expands so much more than air when heated (about 1600 x by volume, i think), which is why steam was used to power much of the industrial revolution.

[@PotterytothePeople]

ahh so smart to make that comparison! Well said.

[@TheMinecraftACMan]

The exact amount of expansion depends a lot on how much pressure it's allowed to build up to. If you look at the saturation curve of water, it can build up a couple thousand PSI while in a saturated state. To keep a very long explanation short, if you have water trapped in a container, there's a specific ratio of volume to mass (specific volume) above which it will be in a saturated state (both liquid and vapor present at the same time). While it's in this saturated state, any increase in enthalpy (temperature specifically 99% of the time) will result in a significant change in pressure (relative to the same change in enthalpy while in a non-saturated state). I would link the wikipedia page, but youtube doesn't like links. You can find the relevant diagram on the wiki page for steam (pressure-enthalpy diagram).

[@jacqslabz]

Tht's what I would going to say: steam engines were very **very** powerful things (at least back in the day).

[@Masqueesha]

As a former pottery teacher, yes, this is a lie I’ve told many times and I knew it was a lie. I was made to tell this lie by the studio owner. They had a weekly firing schedule and if your piece wasn’t dry, 💥! I also had to tell the lie that you couldn’t fire clay that was thicker than your pinky finger for the same reason. Again, because the studio would not allow the time for the work to dry. So glad I work for myself now.

[@SilverSkylark]

I was taught about air pockets causing explosions in school, so it's nice to know it was a reasonable lie to prevent kids from making solid objects that won't dry 😅

[@TheMurlocKeeper]

That sounds disastrous! What a terrible way to run a pottery studio if you're not giving the proper amount of time for pieces to dry? Sounds like someone was a stickler for sticking to a "schedule" under any circumstance, but not understanding that working with clay can't work like that, and it doesn't care about your schedule, lol! It'll take however long it takes, and not before! You kinda have to more "go with the flow", and feel it out. :P I am glad you are able to work for yourself now too! :D Working with idiots would drive me nuts! :P

[@SomePoserStoleMyName]

This may have already been said somewhere in the comments- But, trapped moisture becomes trapped steam which will definitely cause an explosion

[@PotterytothePeople]

yess! 🙌🙌

[@theoriginaltubeofyous]

indeed, water moving to a vapor point expands much more than air ever could edit: vapor state* I meant moving _past_ the vapor point.

[@Juttutin]

Some rough numbers, going from room temp to 900⁰C is going to make trapped gaseous air want to expand in volume by about a factor of 4. So the heating needs to be slow enough for that pressure to either seep out or be contained. I imagine most pottery is porous enough for it to escape before the pressure can build up to anything damaging. Whereas any trapped liquid water, even invisible droplets, is going to expand its volume by a factor of around 1700 between 99⁰C and 101⁰C. So not only do you have the massive amount of expansion, there is essentially no time for the pressure to dissipate.

[@thomasdalton1508]

​@@JuttutinWater doesn't vaporise instantaneously when it reaches boiling point, so there is still some time for the water vapour to escape. That's why the slightly damp pots didn't explode - they were thin enough that the remaining water was able to escape quickly enough to avoid an explosion.

[@oldmossystone]

Yes. I wonder if there might be another parameter too? not a potter here, but my understanding is that there is shrinkage during the drying/firing process? If there is trapped moisture in some sort of cavity, and the walls are thick enough, does the wetter inside shrink more slowly than outside? enough that it can weaken the wall enough to facilitate the explosive escape of the steam? that would mean maybe the ideal environment for an explosion is a sealed cavity combined with slightly damp clay?

[@hoppingwren]

This gave me such an irrationally odd feeling that the air inside the ball is trapped in there forever!! This is air that has been floating around our world for hundreds or thousands of years and now it's trapped in the ceramic ball for a LONG time! An unexpected moment for me, I suppose because everything else in pottery that I've encountered has an air hole!

[@lissicalathairyble5738]

Pottery is porous unless it is fully glazed or sealed in another way. Otherwise, it would not dry.

[@PotterytothePeople]

Such a spooky thought! The sphere will still be porous unless I fire to vitrification. But I might have to do that and have a little air time capsule for future scientists to crack open 🤔😂

[@jenessalarge7621]

I think that's a great idea! But how to keep it safe for all those years ???

[@StealthyMuse]

just wait 'til you hear about bubbles of blown glass ;)

[@MultiSenhor]

Scientists have found bacteria trapped in an underground pool for thousands of years, and recently a still sharp arrow has also been found somewhere else after thousands of years. These things are always mind-blowing.

[@floriangadsby]

Yes! AMAZING - I can't tell you how many times I have to tell people this - and from now on I will send them this video to demonstrate the fact.

[@PotterytothePeople]

Florian! I am such a big fan 😄 thank you!!

[@aaronmcmillin1253]

Big fan of both of you. Seeing this made my day

[@Kraaketaer]

Great video, and I think you're entirely right. One easy(-ish) way of demonstrating this: take an empty pot, cover its opening with a taped down plastic bag or similar. Heat the pot and see how much the bag inflates. Then try the same with a few splashes of water in the pot, allowing the water to boil away. You should see the bag inflate much, much more with the latter, as the thermal expansion of air is _nothing_ next to the volume change of water passing from liquid to gas.

[@PotterytothePeople]

Well said!

[@PotterytothePeople]

One last point because I forgot to mention it in the video! The reason why people think poking a hole in hollow forms saves them from exploding is because that the humid air can escape though the hole! So I do think it's worth putting a hole in hollow forms if possible (like I put a hole in the donut saucers I made a while back).

[@cathleenc6943]

Thank you for this! I made an egg in my pottery class, and I really didn't want to open it up, so now I am happy to know that I can do it again, as long as I get my own kiln or convince one of the local pottery places that has a kiln about the myth busting.

[@walkerpottery9296-Natalie]

Water is definitely the cause of explosions. I had it happen & it was heartbreaking. I crafted a beautiful, huge, one of a kind bird bath for a final project last semester & when I opened the bisque kiln and saw it had crumbled into hundreds of pieces I knew immediately that it was my fault. 😩I totally didn’t allow enough time for it to dry….I got close to my deadline & didn’t listen to my gut. I should tape a picture of it to the wall behind my kiln as a reminder. 🤣 If I could include a pic here I would. This was a great video. Thank you! I missed the donut video & have to find it! 💜

[@candycoatedcactus]

@vlogbrothers John must know!

[@unadomandaperte]

Water vapor wants to expand. It's like trying to cook the proverbial egg in the microwave. 😉👍

[@lornacy]

What about air flow in drying? For things other than pottery, that seems to be a huge factor.

[@nickfoster6081]

I will say that as a public school teacher, some of our biggest enemies are time constraints and environment. Ideally we would like to get everything to the correct hardness/dryness before firing but in some schools there's just not enough space to store work to dry for that long (students also want their finished work super quickly) or the production is rushed because classes are too short and so you get pieces with bits and parts at different dryness and thicknesses. And school teachers, from my experience, also don't often get to control the temperatures in their rooms so you never really know when something is fully dried. I also remember a custodian came in overnight and shut the kiln off which absolutely ruined the students work and upset the temp in the kiln/drying room.

[@nickfoster6081]

I work in the US btw

[@PotterytothePeople]

Totally! I had the same problem in the community studio I ran. Everything had to go from leatherhard to bisqued within a week. Something that saved me was keeping a constant rotation of pots drying on the top of hot kilns. We fired every day so we always had kilns going. Idk if that's a solution for you but that really helped. Otherwise, candle or a very slow bisque ramp will be the key.

[@tkava7906]

Has anyone tried to speed things up with silica gel in the later stage of drying? It absorbs moisture very efficiently. It can be reused (just heat up to release the moisture) and some cat litter products are made of silica gel so it's pretty cheap.

[@dipstrip]

This is what I came to the comments to say, I only took a few us public school classes on the stuff, but it would make sense that a classroom atmosphere would lead to the prevalence of this ~myth~

[@regnbuetorsk]

@@tkava7906 the problem is that the silica gel will have to "wait" until the clay sucks the water from the inside before it can catch any moisture

[@kaytescarlettsenyitko5388]

Back in high school i made an absolutely amazing relief tile. I was very careful to ensure there were no air bubbles. Because I procrastinated, I kinda rushed it through drying. Thankfully it never fully exploded, but now I know why it cracked along the two pieces I put together despite my desperate efforts to prevent damage. The acrylic paint hid the flaws and I got a good grade.

[@freedomstaying-free8162]

Hi again Mia, yes, yes, YES.....I have long held the belief that it's the moisture, NOT the air that causes, not just explosions but big cracks too. Especially in bottoms, which are often thicker than the piece in progress & dry slower. Great video

[@PotterytothePeople]

Yesss moisture & drying techniques are the secret to (almost) all cracks too! 🙌🙌

[@dianadiehl]

Heated air does expand, but moisture (water) turning to steam is a massive increase in volume. Basic physics says the change of state is far more significant in putting pressure on the clay form than simple gaseous expansion. Thanks for the experiment!

[@Nightenstaff]

Yeeep. Steam expansion is ultimately the cause of lots of different explosions throughout many different materials and processes that involve drying. From forges to resin, pottery to baking it's almost always steams fault.

[@gman1515]

I think the reason that your 'wet' pots survived was that they had enough surface area to mass for all the steam to safely escape. The steam needs to be confined for long enough to build up pressure and then that pressure needs to exceed the structural integrity of the clay. I have a feeling if you repeated the ball experiment but fired it at the same moisture level as those pots it would almost certainly explode regardless of how gentle the cycle you use is.

[@lukearts2954]

I don't know how you ended up in my suggested videos, but so far I'm glad I discovered your channel. It would appear that every once in a while, the algorithm does something right =)

[@64DeborahM]

As a novice potter who is keen to learn, your channel is exactly what I'm looking for - I'm really glad to find you here!

[@PotterytothePeople]

wow, thank you! ❤️

[@amys3168]

Great video! I live in humid climate, I use little grog, and sometimes I fire childrens work, sometimes closed spheres. So I candle for quite a while. Sometimes 24 hours. And I ramp up slowly. I hate cleaning and would rather take it slow.

[@PotterytothePeople]

wow thats a long time! I usually candle at 150 celcius for 1 hour and then let it cool slowly. But it depends what youre making :)

[@debsamuels5367]

Hi Mia. Great video. While I agree about the water vs air, I think it might be more complicated. I had 2 small but thick sculptures that were never fired in my first studio. Sat at home drying over 5 years. I drilled into the bottoms and both pieces bisque fired fine. Glazed one and it blew up in the glaze fire. Definitely no trapped water in it. Only 1-1.5" thick. Sometimes there's no easy answer.

[@PotterytothePeople]

That's strange! For sure it's more complicated and depends on the piece & technique. I tried to simplify it for the video. But I am curious what would have caused the explosion here... Maybe too much water soaked in during the glazing process and it wasn't given enough time to dry out? Ah it depends...

[@Briaaanz]

Wow. I really want to show this video to pottery instructors. I suspect some might be interested in testing further while i think several i know will become all stubborn and double down on the trapped air idea. Thanks for makingb this controversial video

[@PotterytothePeople]

Omg yes I just heard from an old potter friend who has been practicing 20 years longer than me that still believes the myth... People will be stubborn! Glad you enjoyed the video :)

[@xxxdoggg]

I agree about some pottery instructors likely being stubborn about this topic. I'm so glad you did this video bc I don't think I would have figured this out myself.@@PotterytothePeople

[@TheMurlocKeeper]

I really hope that whoever you show it to will have more of an open mind to new ideas. It's such a stupid thing to clutch tightly onto to old, outdated ideas, especially when the new information is PROVED! Just because you might have believed something for a long time, does not mean that you can't pick up a new understanding of something! This is why we still have idiots that still believe the earth is flat, lol! Good luck in educating your pottery instructors! I think you might need it. :P

[@dianadiehl]

What might be an interesting experiment would be to make several near identical pieces sequentially so they would have dried a different number of days when you fire them at the same time. Mark each one to differentiate them. (2 days, 3 days, 4 days) See which explodes and which do not. Of course one exploding could break others. Not sure how to control for that unless you had multiple kilns with identical temperatures.

[@Aaakeith]

If you’re doing them sequentially, just fire them in separate batches. Make them all at the same time, but fire one at 2 days, one at 3 days, etc. Would use a lot of energy but worth it for the sake of science 😅

[@dianadiehl]

@@Aaakeith Exactly!

[@chrisinkansas8507]

One thing I've experienced with wild clays where no temper is added is that, even after thorough oven drying (500F), wild clays normally include a bunch of organic material - roots, bug junk etc. Upon kiln firing, the surface can sinter to the point it's airtight, trapping organic gasses that expand and cause the ceramic to bloat and/or explode. Shocked the heck out of me when it happened but it was a good lesson. Added temper would have allowed the clay to breath, preventing the problem.

[@PotterytothePeople]

ahh good point! I hasn’t thought of that problem. 🙌

[@julieanderson8968]

Agree partially to the statement “teachers have lied”. I love that you made the effort to create a myth buster and it was really interesting to watch. ❤ BUT The blanket statement that it wont happen could lead to unnecessary fails and distrust in teachers. Experience is everything in every craft and you have tons of it. I do not study science and have very limited understanding of gasses and minerals but stuff in any studio like: Glazes, clay bodies, people using fabrics brought in, hand creams, coffee, plastics, papers with strange paint or metallic ink or chemicals etc CAN get into the clay body while the process of making is happening. Air expands and Gasses are released in firing and with no where to go will stress the enclosing form to explosion point. As a teacher it is far easier to explain to a beginner potter that trapped air leads to exploding pots. Perhaps a correction to you video is not that teachers have lied but that there is a possibility that it could happen. In order to be safe, Best practice, wedge (for more then just air bubbles), prick a hole in a closed construction OR risk it and other pots around you. 🎉

[@TheMurlocKeeper]

Lol! "wild clay". That brings about such a hilarious visual, for some reason! :P Although honestly, if you've got bugs or root bits, etc in your "wild clay" it means you haven't processed it properly. It ideally should be made into a slurry, (where it can be strained if needed) then dumped on a porous surface to slowly dry out to the usual clay consistency before being cut up and packed into plastic.

[@chrisinkansas8507]

@@TheMurlocKeeper By organic material, I meant whatever's in the clay after processing. Where I've strained through a 150 or 200 mesh screen, what's left is as close to pure clay as I've bothered to go, but, on firing it can sinter up and prevent gases from escaping, resulting in bloating or even blowing apart.

[@clayeasy]

Great video! Great that you busted this myth! I’ve also learned that it’s the air. I still thought so until now! Thanks a lot! It’s time to start talking about moist and humidity instead of air now in the videos. Grusse auf Finnland!

[@PotterytothePeople]

Awesome! Happy to spread the TRUTH! 😆 hugs from Germany:)

[@tnorton314]

So nice to see someone brave enough to carry out this experiment! I've suspected this for a long time for this simple reason: Sometimes I find and pop air bubbles while throwing. But that means I probably sometimes DONT find all the air bubbles. And yet I never have explosions. I wonder though, if you took the clay up past the temperature where it vitrifies, could that trap the air and cause an explosion?

[@heatherpedersen8471]

No, but if the clay softens enough at temp the bubbles will expand and create bumps

[@Momijigari]

I'm still going to dry for a long time and I am still going to put a hole. At my school studio the tech always checked each piece before it went into the kiln and would reject pieces he didn't trust. Over the 3 years I was at that studio I saw plenty of pieces spontaneously disassemble and take out other peoples work. It was always an event which resulted in an after action meeting in the classroom. We were using a gas kiln, not electric, but we would often use electric for the bisque depending on how many pieces there were.

[@PotterytothePeople]

nice! Yes I still 1000% recommend putting a hole (I wish I had said this in the video) because the hole will help the inside of the piece to dry out. I would only skip the hole if it destroyed the function of the pot (ie a double-walled cup).

[@roberttai646]

Great video! You really got me thinking. Try making a solid clay ball the same size as the one you bisque-fired. My guess is that the trapped water in the solid ball will cause an explosion. Just Kidding. Don't do this, it will definitely explode. The operative concept is not water versus air, but "trapped" water. Air can expand and contract, it does that all the time inside of things. It doesn't cause explosions. Water turning into a gas however is a different story. Much more pressure. Much more expansion. All happening very quickly because of the latent heat of water, i.e. heat/energy builds up in liquid water until right at a specific critical point, the water becomes a gas, all at once. Boom.

[@PotterytothePeople]

yess i should have done a solid ball instead of cups. Explosion for sure 😆 but I would fear what it would do to my kiln!!

[@TheFeralFarmgirl]

I was told this when I was in ceramics class. I always thought the fast shrinkage while firing had something to do with it, along with the trapped moisture.

[@oldmanandthesea3384]

I was taught to use the very old kiln that I bought used as a dryer. Prop the lid use just one circuit. Hands are toast these days. Slip is the way for me now. I make my own molds on a good day. Good video. Stay safe.

[@valecbcb]

What I've learned through my journey of being a self-taught hobbyist potter is that what makes the pieces explode is the humidity/water that's inside that when heating eventually makes the water boil and because of that, it explodes

[@PotterytothePeople]

Exactly! 🙌

[@TheParagrine]

Great video. I like your teaching style. I would be interested to see the sphere be glazed and go through a glaze firing.

[@jennyp7084]

Really interesting video. Great to see you being sponsored. Hope Babbel sponsor more videos.

[@PotterytothePeople]

thank you!! 😄

[@natashanewman2296]

I knew it, thank you for proving this. Now i an reference this video the next time someone tells me my sculpture needs holes poked into it. Thanks for being brave and confident and testing this out!

[@alleriodrone]

I remember spreading this misconception at a summer camp I did pottery at. We only had a week with the students so there was no way we'd be able to fully dry it for them to fire it correctly.

[@fahadalassadi]

Helloo, you mention that your pot being cold to the touch can be a sign of how wet/dry it is, do you think that a piece that holds temperature less is more likely to be dry?

[@fraujohnsen6189]

The reason fir it to feel cold to the touch is the evaporative cooling of water. Water needs energy to evaporate, which is "taken" from the surroundings temperature. It is the same effect as sweating or being really cold after coming out of the pool and not drying with a towel.

[@PotterytothePeople]

Honestly no idea, it was just taught to be somewhere along the way by another potter, but what @fraujonsen6189 sounds convincing to me!

[@IAmCraftingAgain]

I always was told this. But also that thick things exploded. So those dont go hand in hand. What you are saying explains so much. The effects you could make with air bubbles below a thin layer of clay....

[@gaylordzapikowski9053]

The thumbnail had me in stitches, exclaiming "who thinks pottery is air tight!" as my many potted plants look on, their pots caked in calcium accretion from the tap water that had fed them in years past. Of course, I didn't know the extent of the myth yet, I didn't know explosions would be involved.

[@nixxonnor]

Nice explanation. Wouldn't it be possible to use an accurate balance to figure out when the clay was dry enough? Like when a certain piece has lost 2.0 % of of it's original weight? I don't actually know what the relevant weigth loss is for fresh vs. "burnable" clay.

[@tammyandkiki]

Absolutely wonderful video! I’m glad you did this. I’m a Hand building Instructor, and I always tell my students this. Good idea to do with students to show them firsthand that it’s the moisture in a piece, not air ❤ The leatherhard- 😂 cool!!!

[@PotterytothePeople]

thanks!! im glad you like the video! ☺️

[@MsBlulucky]

I get where the myth comes from. It's basic physics: pV=nRT slightly simplifies explanation: n is the amount of gas molecules and atoms, which obviously doesn't change in a closed space. R is a constant which means it doesn't change either. V is the volume, so another constant in this case. T is temperature and p is pressure. Therefore if we raise the temperature, we also raise the pressure. The idea that trapped air can cause explosions is the opposite of far-fetched! So either the higher pressure is not enough to lead to an explosion or the clay isn't airtight and therefore not actually a closed space. I don't know much about pottery, but if water can evaporate from the material, then I wouldn't be surprised if it also lets though air molecules and atoms.

[@AngieTheCatGD]

1:58 its not overkill, its overkiln

[@jgplayz]

When gases (air) and liquids (water) is heated it expands. However because gases are compressible they become pressurised but water can’t be compressed so it forces out causing an explosion

[@rosehawke2577]

I only threw for a couple of years over 20 years ago, but the *only* time I had a failure was pretty obviously from trapped air. A largish flake popped off a mug and left what was obviously an air pocket. I mean, it was a little hollow. My fault for not noticing it in the throwing (I was just a bit beyond rank beginner,) so it *can* happen, just not catastrophically like the pix you showed in your video. I've actually still got the mug, I turned it into a pencil mug.

[@syriuszb8611]

I'm just watching the videos about pottery, never did any. But I knew about water being the main reason behind cracks and explosion. I think most people who explain those things on yt do say those. Maybe sometimes they say air as a quick comment, but I have never seen anyone proposing that air and not water is the cause behind explosion. BUT I do believe that sometimes air can cause cracks, maybe even explosions. But only if you heat or cool down piece very quickly, which everyone is trying to avoid anyway.

[@loganpenney3185]

Great video! Maybe you could make two identical spheres let one dry and fire one after a week when it "looks dry" to see if its the water that makes it explode

[@gabrielabukovacova-bartoso303]

Hi Mia, always withinthe kiln opening I waited any "wow" scenario and there was nothing 😂 you are the best ❤ thank you for inspirative video and time to spent with this test !!!!! 😊

[@zaz131313]

Is it possible to glaze the ball? Would the glazed surface trap air which would expand in the heat?

[@scattered-idea]

This makes a lot of sense, nice video! But I was wondering… I once made a mug, it was fine as biscuit but after glazing it kept on cracking(it’s in one piece but the glaze cracked and it kept making a clicking noise once in a while). Do you know why that might be? I’m a complete beginner and I have no idea😅

[@PotterytothePeople]

That sounds like a glaze fit issue! Simply said, glaze shrinks too so if they clay & glaze shrink a different amount, the tension can cause cracking. I have a video from a year or two ago that covers all kinds of cracks. Maybe that can help you!

[@scattered-idea]

@@PotterytothePeople thanks a lot :)

[@DanVogt]

Thank you! Phenomenal video. Great presentation and instruction, I'm very thankful.

[@karri8998]

Would like to see you fire a similar ball that is leather hard dryness. Yeah I want to see the explosion, lol. Thanks for the great video!

[@PotterytothePeople]

Maybe I will do an update video :)

[@Susan-gi2cd]

Hi Mia, thank you very much for all your videos, you are an excellent teacher. I was told that any little bit of grit or dirt in your clay will cause an explosion. Is this true?

[@PotterytothePeople]

it can perhaps depending on what it is… it would have to burn off a LOT of gas though to cause an explosion. It’s more like to crack or just bloat the clay i think.

[@retrosimmery]

Thank you so much for doing this experiment! I've been marvelling at some ceramics at a local gift shop that are completely closed forms and wondering how they didn't explode! My big takeaway is to dry a closed form piece for 2-4 x as long before firing as I would one of my normal pieces. (My environment is fairly dry and I can fire within 4ish days on average).

[@PotterytothePeople]

Exactly! Lucky you on the quick drying time! That can be a game changer as well 🙌

[@gingermany6223]

There was a maker at Open Sauce who makes double walled insulated ceramic coffee mugs that don't explode! Used a mix of 3D printing and traditional slip casting to make them.

[@ixchelssong]

What did s/he do with the 3-D printing? Was it just for stencils or forms?

[@gingermany6223]

@@ixchelssong weird my first response was removed. His name is Chris Pratt with Pratt Ceramics. The 3D printing was used for forms and pieces for automating the process for small production. Pretty cool stuff.

[@creativehands4361]

Thank you I totally agree with you, things can be wet for weeks and you not realize it

[@PotterytothePeople]

Yess exactly 🙌

[@OriginalLacytoo]

Hi Mia - great video. I hand-build and pit-fire with wild clay. I use some temper but apparently not enough as many of my pieces end up with spalls. Could be moisture…..Frustrating!!

[@PotterytothePeople]

Wild clay is it’s own beast! I wish I could help but I dont have enough experience!

[@OriginalLacytoo]

BTW IMHO you are awesome. Love me som Mia!

[@meowwl]

Fun fact...Clay is made up of tiny plates that tangle and stack together. Water acts as a lubricant between them, letting them slip past one another, allowing it to be formed. As the water evaporates, they lock together, forming the shape, but also leaving tiny voids, leaving the clay porous, but also potentially trapping water in pockets. The air bubbles that cause the problems, also create that same humid microclimate, inside them, which also functions to keep the inside of the bubble slightly cooler....And since all the clay around them is dry, it sinters (slightly melts, fusing together) first, and forms what is essentially a cyst around both water and the air, sealing it to varying degrees, depending on the porosity of the clay, and when the heat reaches that cyst and evaporates the water, and heats the air, causing it to expand as well. Sometimes that only results in a weird little bubble in the clay, or a crack in the body of the work...But if it seals, you get an explosion, from gas, both the air, and the water flashing to steam, expanding too fast to escape through what porosity is in the clay. That's why you wedge clay before you use it, to get rid of those small to medium sized bubbles, and to evenly distribute the moisture, so it doesn't so easily collect in those ready made pockets. Ironically, the size of that sphere might have contributed to it's survival, since there is more room for the expansion, and more area of porous clay, to let it out without breaking. Though if it were made of a less porous clay, or were glazed over the entire surface, I would bet you'd run into serious issues. In truth, modern kilns, with their better temperature controls, make actual explosions a pretty rare thing...their programable slow heating programs make sure that the entire body of the clay is dry, and will let the trapped air and water slowly exit through the pores in the clay.

[@donaldasayers]

A long time after I made it, I broke one of the stoneware pots I made at school, I found quite large voids inside which puzzled me for a while. Til the clay is fully vitrified it remains quite porous, so air and water vapour can pass through it, how else would it ever dry out otherwise? If the temperature rise in the kiln is slow enough, any trapped air will simply diffuse out through the porosity of the clay. It would be fun to see what would happen to your hollow sphere if it had been taken up to a fully vitrified firing.

[@lorenasafa9854]

Thank you so much for the time you took to maje this video!!!

[@klaernie]

I wonder if measuring the weight of the moist clay and the same lump thoroughly dried might give a solid understanding. Than one can calculate how much water is stored in it. And with that info one can measure the initial weight of any piece of pottery fresh of the wheel, and calculate how much water needs to evaporate for it to be dry enough to be fired safely.

[@shannonsteven808]

Thanks this was super helpful!

[@ShweMyaukMyauk]

Babel needs to sponsor more videos 🎉🎉🎉🎉

[@PotterytothePeople]

Thanks for your support! ❤️

[@walkerpottery9296-Natalie]

Hey! I wasn’t able to find that donut video. Any idea where I can find it?

[@kinakomochi_cats]

This is interesting. I knew it was the humidity causing the explosions but my teacher told me that a completely closed shape will never be able to fully dry and therefore can't be fired. She said the microenvironment inside will always stay moist. But this proves is possible! Still, I won't risk it in a communal kiln, but it is great to know if I ever have my own kiln.

[@clarkington_uk1567]

I have only just found your channel and I love it!

[@PotterytothePeople]

thanks so much! welcome! 😄

[@Kram1032]

This is probably really silly but is it possible to *freeze-dry* clay first or would that just completely fail? Or how about using different liquids (oils, alcohols, ethers) which may behave very differently in this process? I'm guessing those might fundamentally change the situation...

[@Ravaxr]

Coming from someone who ran steam engines: It makes sense that water is the main problem. Using ideal gas law( PV = nRT ), trapped air will apply around 5 times its pressure in a kiln at 1500K compared to room temperature around 300K, assuming the air pocket is impenetrable and stays the same volume. For every liter of water, at atmospheric pressure it turns into 1600 liters of steam at 373K, and only gets worse with ideal gas law as the temperature increases. It only takes a few drops of water to exceed the expansion rate of the air inside the sphere.

[@PotterytothePeople]

Love a scientific explanation 🙌

[@luziapottery]

whats your biscuit temperature curve . I want to know as it seems to give a bigger chnge of non completly dry pieces to survice haha , thanks a lot for this

[@Bobis32]

in school when i did pottery we stored pottery waiting to be fired in the kiln room for about 2 weeks(minimum) before firing, the kiln was almost always firing something so the room stayed around 120f and was quite dry thanks to dehumidifiers

[@sporkymail]

Great video! I reckon you should do another proof where you run a harsher fireing program the explodes the wet clay but the same program doesn't explode the trapped air. Because technically you have only proven that your fireing program prevents explosions

[@danielluher7975]

I don't know if anyone said this yet, but I appreciate the scientific approach you used and the honesty when the pots didn't explode. Some people would not have, and that's fair, no one wants to be wrong, but I think it's important to show how the experiment went, even if it wasn't according to plan.

[@Pikachew675]

I was never told this myth so now I want to know

[@bigbomb5904]

Can you explain why it may crack in the kiln

[@peterlee9691]

Water does expand into steam a lot greater than just air alone, but if your clay thickness is able to withstand the expansion before it cracks slowly or explode rapidly it won't break. So try the experiment with an air cavity on a thinner clay wall instead. And perhaps fire it up rapidly instead of slow and gradual which won't allow hardening and expansion at an equal pace.

[@wrekced]

This was very interesting. I do wonder how that sphere would fare in the kiln if you glaze it. I think that, depending on the type of glaze, it would have a good chance of exploding under those conditions. Gasses from the glaze might pressurize the interior leading to an explosion. I would love to see that tried!

[@lamardon9723]

I'd say that the sphere has enough porosity to allow the expanded air to vent with the gradually hotter kiln. Is this the case?

[@lukearts2954]

Of course the actual reason is water turning to vapor. I think using a wrong cycle (too hot too fast) will also make things worse. I hear a lot of stories about explosions from school kilns and the like, because they often try to bake overnight instead of a full 24h cycle. Water evaporation increases the volume x1000 (or more) in "normal" pressure environment. This is a number we (firefighters) use when making calculations for sprinkler systems or fires inside solid structures, to avoid overpressure and other issues when too much steam is generated. (superheated steam under pressure is more dangerous than actual flames for a bunch of reasons) When in pottery water is trapped in a small pocket inside clay that has solidified, this also means the pressure in that pocket will go x1000, which no clay will ever hold. If during the evaporation there is still a path for the vapor to escape, for example through porous or unbaked parts (or the poked hole that you mentioned in your pinned comment), and it can escape fast enough, the object will not explode. *_If you want to ensure explosion,_* make a pocket by folding over a layer of clay, compress it without kneading. This will most likely create a pocket. If you do it with extra water on the surface that you fold shut, or you rub more water in to camouflage the seam, you'll have the perfect recipe for kabooom... The essence of what I'm trying to say is, that it'll take a lot of coincidence to explode pottery that is homogenous, regardless of insufficient drying, because the main factors are actual _small_ inclusions or pockets of water (with or without a little bit of air), and too fast evaporation due to faster heating or too high temperature. The larger the cavity, the smaller the chance of explosion. So I feel that the large sphere didn't prove anything, despite your theory being absolutely correct =)) (I also think that the idea that it was air that made the explosion may stem from what they found after an item exploded: the cavity that held the water will have been enlarged before fully firing/baking, so they will find parts of cavities in places of the item where no cavity was intended, making it seem like it was an air bubble that exploded, rather than a waterdroplet-turned-steam bubble.)

[@monkeychicken27]

The rare closed form I make, the shrinking causes a bloated form around the trapped air. The pot likes to pop or rip a seam or any tool mark so it would never get to the kiln. I’m guessing the walls of the piece in this demonstration were thick. Also, I’m curious of what tension it might be under post bisque, and…through and after a glaze firing.

[@Mistwolfss]

1:30 waterakes alot more sense because going from a liquid to a gas is alot bigger than going from a gas to a bigger gas?

[@spiltmjlk]

I will never forget the first time I ever had a clay project explode (or in this case, shatter) age 15.. had finally completed a clay sculpture for a final art assignment, it was an oddly proportioned person being dragged into the ground/ surface it was laying on by two red hands. I was pretty proud of it as it has been the first serious, larger attempt at making anything with clay. I had let it dry out for a couple of days before bringing it in to school to be fired before the deadline the teachers had set. Everyone else's sculptures came out fine, and I was waiting to be able to get mine until my teacher pulled me aside and told me my sculpture had shattered. The entire head had snapped off the body and the body has shattered almost entirely. I played it off pretty good, saying it was fine - it was annoying yes - but it was fine. It was not fine. I went to the bathroom and cried for like 3 minutes before going back to class. I then had to spend days, weeks, recreating my sculpture and it was no where near as well crafted as my first attempt, but it survived at least. It was most definitely moisture that had not yet been released that caused the body to shatter. Every time I see the broken head or the full second version (which are both decorations in my parents home), i get filled a minor amount of rage.

[@emunah21]

I love your channel! Could you teach us how clay is painted, like animals, flowers? Is it with special pens? 💗🌞🤩 thank you!!!

[@Santibag]

It's even crazier in metal foundry working. They are normally water free, unlike pottery. But a little water touching hot metal evaporates so fast that it explodes. Your mild program might be drying the pottery while it's in the kiln, which is a more expensive but faster drying process. You can technically even use the kiln as a dehumidifier, but kiln will throw away some heat with the steam. Dehumidifier with a compressor is much more efficient. Kiln has a dehumidifier COP(coefficient of performance) of around 1 at most. Dehumidifier with a compressor can have something like 3. It means, it's like 1/3 cost of drying.

[@notamouse5630]

Of course water, or most other liquids that vaporize within the temperature range of the kiln. Water expands 1700 to 1 and then more due to superheating in a kiln environment. Extreme example: 1ml of water will become a minimum of 1.7L of steam at atmospheric pressure. Constrain that and the math gets complicated and involves tracing water's phase diagram, but generally speaking it would probably get to around 2-10 atmospheres and/or explode. No, that is not particularly safe at the 10 atmosphere amount even with the walls of a kiln. I am an engineer, though the above amounts to crude calculations and engineer's "professional common sense". Perhaps an old microwave could be a crude hydration tester by heating the piece to a temperature proportional to the water in it for around 30s. In the case of 1ml of water inside, the relatively durable steel inner walls of a microwave could be a durable or cheap and sacrificial test to save the kiln. It could even be used as a fast drier for some clay mixes, though it could crack from fast shrinking on fast drying and that is not advice.

[@KnKlco]

In highschool I had an overdue art assignment, a life size sculpture of a hand, that needed to be ready to load in the kiln by end of the next school day or I'd get a zero... And I hadn't even started it. The art teacher was incredulous and half mocking when I said I was taking a lump of wet clay home and that I'd bring it in before school fully bone dry. She claimed it was impossible, and *insisted* it would explode when I shared how I planned to dry it in the oven I went home and built it as if half protruding from the table to eliminate the bulk of the meaty parts of the palm, so it was just under an inch at the thickest. After dinner I stuck the not even leather hard piece on some metal screen onto the oven grates, and turned the oven to 175F with the door cracked a bit for humidity to vent. Before bed I set it to 200F, woke up a few hours later and set it to 225F, and a few hours more and set it to 250F. If it was going to explode it likely would have already at that far past the boiling point, so when I actually got up to get ready for school and set it to 450F for a last hour, it was an overcautious step done mostly to be a smart@$$, since I then brought it to school insulated in a towel and still burning hot so that she had to acknowledge it was irrefutably bone dry. (and unexploded)

[@barongerhardt]

Air could be the cause of some problems. As the temperature increases the air will try to expand. If it cannot increase in size or diffuse out fast enough, the pressure will increase. At some point that pressure will exceed a critical point and fracture the pottery. It is far more likely to be related to liquid water because the vapor pressure increase much more rapidly. Room temp is about 300k doubling it to 600k (300c) would double the internal pressure. The vapor pressure of water at 100c is about 1 atmosphere. Rising just 75 degrees to 175c is around 10 times higher pressures and another 10 times (100x total) after another 75 degrees. That continues until either the liquid water is gone or pressure decides to make its own path. It is also of note that to double in volume and hence negate a doubling of pressure a bubble only needs to get about a 26% larger radius.

[@espressomakesmep00p]

I always put an extra 3 hours under 100 degrees celsius (around 60-70) step so it will dry pots if they have a bit of water in them. Life (or should I say pot?) saver!

[@PotterytothePeople]

smart! 🙌

[@hollygauthier5691]

Very well explained. Ty

[@remjoleea5560]

I took a pottery class my senior year of high school and I only had one project explode, thank god. It was a pretty thick sculpture (seal type thing) so it makes sense it didn’t dry all the way.

[@elementaldraco]

I was always told to be careful with molds made of plaster of Paris because if any of it broke off and got in to the clay. It would end badly when it was fired.

[@ThorStroliaDavis]

I have a theory that would be cool to test. I think you are onto something with the inside environment but I think it is less to do with the state of the clay and more to do with the inside humidity, as you mentioned. My hypothesis is, perfect world, you have a completely dry shell but there was somehow a humid environment inside that in some way added no moisture back into the inside wall of the clay, I think it would still break because the moisture is expanding in the heat creating a lot of pressure on the inside of the ball. Drying the clay as long as you did allows the inside moisture to reach equilibrium with the outside environment creating a low moisture inside environment reducing the amount of expansion inside the ball. A perfect world test would be hard to do but you could make a ball with a small hole in it just big enough to put a balloon inside, and then dry it completely the same way you did before, then put a balloon inside and fill the balloon with a half teaspoon of water and fill it the rest of the way with air. The balloon would retain the moisture preventing the clay from gaining additional moisture until time of firing. Then close up the hole and allow it to dry as well so the balloon is inside the completely enclosed dry ball. The balloon will melt causing it to pop in the kiln, this would be intentional, then allowing the warm humid air to come in contact with the ball only after the firing has begun. Then I believe the expanding gasses would hopefully in my experiment still cause the clay to break.

[@delaterrealaprise]

What a interesting video !!! Thank you so much for this. That'll change a lot of things for me. But I mus say : there is still a thing I don't understand. the air expands by heating. Ok, the clay remains porous (you mentionned 900°C, so I guess the air can more or less "flow through" the walls of the ball), but what if you fire to vitrification ?

[@PotterytothePeople]

I think the air will expand faster than it can seep through the bisque pores (not totally sure about this) BUT there's nothing wrong with a little pressure being built up. If I fired the sphere to vitrification, the air would no longer be able to escape, it would just be pressurized (and then lose the pressure when it cools) but the pressure wouldn't be enough to break the walls unless they were very, very thin.

[@omerio911]

I did some rough calculation, and if you heat up the air inside the sphere from 30 degrees to 900 degrees the pressure inside would be around 3.9 times larger. If you have 1mL of water inside a 1L closed space the pressure would double (in addition to the increase from the air heating) which results in pressure around 8 times larger. Since there isn't a lot of air inside even a small amount of water has a significant effect on the pressure once it turns into steam.

[@JeaniePalmer-c8y]

What about the fact that the clay is shrinking while the air is expanding in the heat? We can't even let a sphere dry like you did without the internal air pressure cracking the piece - much less putting it through the kiln. It may be the shrinkage rate of our clay vs. yours, but I don't think it is just moisture that is the problem.

[@pestalinc]

In Highschool i made and Eyeball and had to convince the Teacher that my project would not explode before they would fire it. It was a hallo sphere (the Eye) with the eyelid wrapped around the whole thing. So it looked up when placed but was still basically round. My dad did ceramics and i worked one of his friends shop as well. So i told my Teacher i would just take it home and fire it. He finally gave in but placed it on the top shelf by itself just in case. Came out great.

[@barfy4751]

@Potterytothepeople I wonder how the pottery would behave if you put it into a vac chamber before the kiln

[@aimsical285]

Makes sense! As an elementary school student I got to do a fun clay project. I made what I thought was the coolest pinch pot bird, but I completely forgot to hollow out the head. ( I was probably 9 years old...) The head cracked off right at the "neck" which was at least a better outcome than exploding. The trapped water theory makes sense because it was a 2-3 inch solid sphere of clay that probably didn't dry out fully

[@potteringaroundtheworld823]

Thank you 🙏🏼 best information ever 😀☺️😁

[@fluffycritter]

A big part of it is that the phase change from liquid to gas does way more expansion than how much air expands when heated up. Air going from 30°C to 1100°C will only expand by a factor of 4.5x, which isn't all that much pressure and is certainly tolerable by clay. But water going from 99°C to 100°C will expand by a factor of around 1600x, and then the heat from 100° to 1100° is another 3.5x on top of that - that's an expansion ratio of around 5600x, all told, and is an *enormous* amount of pressure to hold.

[@cjcarver6290]

With your years of experience, are you able to tell if a project is still wet because it feels heavier than it would when dry?

[@PotterytothePeople]

Mostly yes! But with different sized pieces & thicknesses, sometimes I am not sure. With my pottery it's usually straightforward, but student pottery is always harder for me since it's usually a bit thicker and I have to have quicker turnaround.

[@coryart]

Can't you "'quick" dry in an oven? Like over night at a low temp? I have never made clay projects.

[@flamesofhellstudio]

What is grogged clay? what does that mean to grog it?

[@SashaKotliar-m3w]

it make much more sense that it's water rather than air, you can see it also in cooking for example in bread baking and egg frying, or even when you add water to a hot oil, the oil escalates the water heating & the water rashes to escape resulting in shooting everywhere

[@space1464]

Hello, I am from Kiev and I want to tell you my sad story about my first clay art. I remember, when I was studying at an online school, we went on a field trip to a pottery club. It was a very nice place and the decorations made it look like a real Ukrainian village house with a garden. Everyone who wanted, got a piece of clay and we started. I made a miniature little jug and a few cups, which looked very well. But since it was not a very professional pottery club and children came here just to play with clay and have fun, there was no baking included with the tour. Also, the day we went there was white clay instead of brown clay. And it was very sad and unfair, because it meant that I could not bake it properly since we, like many other people had just an ordinary oven which was of course, not hot enough for white clay. And even though unlike other children, I made a miniature, but profeccional realistic jug, I was never able to fully complete it. If only the tour guide understood the pain... But at the end I coloured my tiny tea set with some paint, and even though it could not hold any water, the result was still beautiful.