Crucible Tempering Revisited: To use borax or not? or something else?

revisiting crucible tempering these things are really heavy it echoes when i talk like this i've talked about crucible tempering before but now that i have this new kiln with this thermocouple and it's very easy to control i decided i'm going to screw around a bit since i had two crucibles that i had yet to temper so originally my previous video about crucible tempering basically all i did was heat it way up and let it cool down and i did that and i did that with this one this big honking one as you can see it changed when you get them they look kind of like this it's a it's some kind of clay i assume with a buttload of graphite in it it certainly looks like graphite and as they call it graphite clay you know it's i don't think it's a major stretch of the imagination but this is not not super highly fired i'm assuming here just assuming they they have this this kind of mix this clay mix that can handle thermal shock and they press it into mold this looks like it's molded it comes out of the mold they probably do a low fire which kind of it burns out any any residual moisture like and not just moisture but like chemically bound moisture and then kind of it's basically takes all the particles and centers them together so they're stuck they're all stuck together turns it into a ceramic you know i don't know if you can hear that this is definitely ceramic but they advise you you temper it first in my previous tempering video all i did was heated the sucker way up let it cool down and it turns into this that's what i did to this one in the in that that well that clean up video this was going in the background heated up i said i was going to 2000 actually went to 2100 degrees heated it up and it looks quite different close up you can see a little it looks like little balls of glass came out of there that's because one of the major components of clay is silica which is the same thing as glass and firing it melts melts the silica that does a couple of things it makes it makes the the the clay less porous it also takes all the sintered particles you know they're just kind of stuck together melts them and they flow together into one into one piece so basically as you're doing that you're you're you're turning centered metal into like cast metal to use a metal analogy so instead of the bits being stuck together they melt together and form one piece that makes it stronger generally with metal with uh with ceramics i mean the hotter you go the more fused together those particles get it makes it stronger which is nice it's not it's it's not wow that's wonder which one of those got my hands so dirty it's it's not all like sunshine and rainbows though because the more fuse they get the hotter they get the stronger it will ultimately be but the more it shrinks so it can deform more the more it uh well the more it has a possibility of deforming and if you get it too hot it just straight up melts into a pile on the ground so there's there's a limit so if you've done any research on tempering crucibles you might have been expecting this to show up and now it's all over the floor borax borax and boric acid are two very common treatments that people put on the crucibles for tempering purposes it actually says did i just wipe that on my face i'm gonna leave it some of the crucibles that i've been getting won't say anything about tempering some of them came with a sheet of paper that talked about heating it up red hot letting it cool off before using it and some other ones talk about using borax to treat the crucible now borax the reason it works so well it's a it's a flux it's a very strong flux fluxes try to get a good solid definition but it seems to be all over the map they're used for cleaning stuff cleaning you can clean metal with them you can make things more more flowy so you can click so like in a molten metal puddle you pour in borax makes it more runny it binds to the crap runny metal will let all the crud float to the top because obviously everything's lighter than the metal it's it's it's overall pretty nice in ceramics it can cause some of those parts those sintered parts melting together causes them to melt at a lower temperature so it's like water and salt so you have ice water will freeze to ice at 32 or you think about it the other way you have ice you have to heat it to 32 to make it melt if you add salt or maybe borax i don't know if you add salt then you don't have to heat it as much to make it melt you know you'll heat it up to 28 maybe and it'll melt but then it'll cool down it'll solidify again at 28. it's a similar thing with with borax and particles in the clay i think it causes mostly causes of silica to melt the glass part so it's like clay generally has silica the glass part alumina which is like a stabilizer and some amount of fluxes i'm going to stop doing that and those have to be in balance to make sure that the parts melt together make it strong but not too melted together at whatever target temperature you're at with these crucibles i'm not sure what target temperature they have but they say they can handle 2 900 degrees so i'm basically thinking i'm never going to get it hot enough to melt the crucible part clearly though i'm melting the glass part out so why wouldn't you use flux well the one i showed you just now was heated at 2100 degrees didn't use flux at all and clearly the glassy stuff's melting out if you put the flux in borax borax is a really strong one uh boric acid is probably better it's not quite as strong they're both borates a molecule of boron and oxygen but the the molecule in boric acid is a little less aggressive it doesn't damage stuff if you put flux on your crucible those particles will melt at a lower temperature so you'll be able to temper it so you'll be able to temper it get it all those parts all that stuff totally melted and fused together at 1500 degrees instead of 2500 degrees that's pretty significant the issue is it will re-solidify it'll harden when it cools and then the next time you heat it up that hot it's going to melt again so it'll in a sense accelerate the thing melting and crumbling apart and i had a crucible to show you when i used to use a lot of borax and it basically turned into rubble like a block of loosely held together uh gravel it was it was bad so my goal here with both of these crucibles i'm just going to use them for for aluminum and zinc alloys low low temperature melting things i'm going to temper them much hotter a much higher temperature than aluminum let them cool off they will then be tempered fully fused all the particles fully fused and then i will never get them that hot again they'll probably be 500 degrees shy of what i'm going to heat them up to so i hope they will permanently not fall apart because i won't be pushing them up to that melting temperature over and over and over and over and as an example of that off the shelf here is a crucible that i temper i think this this might actually be the one that i tempered in that video and i've only used it for aluminum and it looks pretty good it hasn't hasn't really changed much it hasn't worsened so much while hang on where did it go there we go while this one this one same crucible same company tempered the same way i was using for i think i'd use this one for the silver the silver melt remember when i did the silver sword and then the copper ones the copper stuff and the bronzes and stuff so this one sees higher temperatures and look at it just look at that thing that's that's looking it's looking considerably more more corroded and the inside's also kind of rougher and nastier and but this sees temperatures five or six hundred degrees hotter and it's done it multiple times so if this if this thing were treated with with a butt load of borax it would uh it would probably not be holding up anymore and i know this is really strong and i know that because i actually had this sitting on the power wheel jeep and i knocked it over and fell onto the concrete floor and it didn't break that's lucky the clay is really tough but it's mostly tough designed for heat thermal shock you know not not really like if you drop it it's still going to break so if this one was done in the old method and this one isn't done yet what am i gonna do well i'm gonna do something different he did that one in this thing watching that thermocouple up to 2100 degrees with no flux but for this i'm not going to use borax because i don't want to ruin my crucibles prematurely i'm going to use as a flux what is in this non-descript paper bag full of mysterious white powder just kidding it's called whiting it's uh it's calcium carbonate it's a molecule of or it's a it's a mix of like calcium oxide and and co2 molecules and i am going to apply that to there much like people would apply borax and see how it works so why am i using that instead of borax like normal well borax boric acid they contain borate different different kinds of borate and that is a flux there are a lot of these fluxes there's there's like like magnesium oxide is is a flux sodium sodium can be used to flux sodium like i talked about table salt you can use that as a flux lead lead oxide that was a fantastic one for a long time for a lot of reasons and they don't use it anymore not if they can help it for very good obvious reasons mostly that has been replaced by by borates anyway i think i think i heard someone i read somewhere that like the the far left two columns of the periodic table all of those as oxides work as fluxes and then a bunch of the rest of the things as oxides work as fluxes and calcium carbonate contains calcium oxide which is a flux but unlike borax unlike borate in general it doesn't do diddly squat below about 2000 degrees so i'm gonna heat this up to 2100 degrees it it doesn't start fluxing until like 1900 1950 and then it doesn't flux very well and it the fluxing power works a lot better the hotter it goes so i'm going to cover that in this heat up to 2100 for a while see if it'll do the fluxing action then cool it back down then i'm hoping that it will never see hot enough temperatures for it to flux anymore so unlike borax which will continue to flux everything every single time you heat it up accelerating the damage of the crucible this should not that's the hope anyway i'm also not going to use that much of it oh and because this is a lot of extra hassle i'm probably from now on never going to do this again but hey i got the equipment to test it might as well might as well give it a shot eh to apply it i'm going to dump this some of this not all of it just a bit in here stir it all up and then i'm going to dunk the crucible in the the clay is semi-porous because it's not super vitrified not high fired yet and the water is going to wick into the clay and deposit the the whiting here on the outside and then i'm going to not screw with it because it's easy to knock off at that point dry it and stick it in there and you know do do its thing and i'm explaining this all now with moving hands and not doing it because anytime you have some powder this fine you really ought to use a respirator so i'm going to stop talking and jam that thing over my face so the way i'm mixing this i'm basically just taking taking some cupfuls of it and dumping it into the bucket of water i'm not really measuring it the idea here isn't to make it like a certain thickness i'm not trying to like paint the thing on i'm just trying to let some of it soak into the surface of the of the crucible and then to mix it up i'm taking a it's like a mixing thing on the end of a drill for like paint mixing yeah it works pretty good for mixing anything in water and just kind of going to town on it it's not milk don't drink it and then to apply it i'm just i'm just filling the thing up basically dunking it in there and filling it up as long as there's like as long as it's coating the whole thing and it's and it's submerged for for a little bit like you're not painting it on the outside you're actually dunking it in letting the water wick in to the crucible and then and then that deposits some of the whiting on the surface and in the little nooks and crannies and what have you and i should probably mention don't just dunk it in water and throw it into a furnace because like it's soaked in water now you know that's bad idea let it dry first or if you can't possibly let it dry you can do something called called uh candling you basically heat the thing up to like 150 200 degrees and hold it there for a while you know that that's that's basically like speed drying it like heat it up for a while and then then after you're you're you're assured that it's not got any water in it to go boom when it when it boils then you can heat the thing up all right next day let's see what we got you know i see a difference this is the one without being coated in anything okay that's the one with being coated in something fired exactly the same thanks to that uh thermocouple there within a couple degrees actually this this one that you saw me put the whiting on this one actually was probably fired like 10 degrees hotter but i mean what's 10 degrees more or less but look at the difference these are from the same company uh they came at the same time order at the same time fired in the same thing with the same bottle of propane don't know how much same year you can get except this one was coated in the whiting and you know i don't see a terrible difference other than uh these vitrified chunks look like they've balled up a bit bigger than these and that that kind of makes whoa well they're they're rolly and that kind of makes sense because like glazes that are high in whiting form these like rivulets and they in the it kind of alters the way that the melty bits flow and stick together quite significantly more so than borax let's take a look inside the the poorly lit insides yeah they're i don't i don't see a huge difference maybe on the tops now it's consistently consistently this vitrified thing has has balled up differently than the vitrified stuff here and neither of these crucibles will ever again see that high of the temperature because i i intend for these to be uh to be zamik and and aluminum only there's that a vaguely scientific test with no real results and i'm not going to bother doing that thing anymore i'm just going to do it the way i did this just stick it in there heat it up so uh today we have learned absolutely nothing hope you enjoyed so you

Channel: Paul's Garage

Views: 23,872

Rating: 4.9118328 out of 5

Keywords: metal casting, melting metal, how to, graphite crucible, how to temper a crucible, graphite crucibles, preparing a crucible with borax, glazing crucible borax, crucible seasoning, preparing a crucible for casting, preparing a crucible for melting down, how to make a crucible, paul's garage, making a crucible, diy crucible, sand casting aluminum

Id: 6bd_Lsteryw

Length: 15min 50sec (950 seconds)

Published: Fri Nov 06 2020