Chilly

What they are telling you is true.  I used to melt a lot of glass into the bottom of small pots.  I actually had a small sliver come loose and cut a person.  Not badly, but that stopped me in my tracks.  And @Callie Beller Diesel and @neilestrick are correct about the explosion.  I had a smaller incident with glass in the kiln.  It's simply not a safe practice.  If you have seen commercial coasters with some sort of melted glass in them, I surmise that they were treated with a form of resin to seal the glass.  I have one on my desk.  Which is what prompted me to try it in the first place!  Live and learn.  
Roberta

The glass has a  very different COE (coefficient of expansion- different shrinkage) than the clay and glaze, and it most likely put a ton of stress on the coasters and blew them apart.
To get the piece off the bottom, try sliding a pallet knife/scraper under the chunk. You may lose a little bit of the floor but that won't hurt anything. If it has melted into the floor a bit, put a thick layer of kiln wash on it for the next few firings until it stops melting.

hello, kevin,
i have been single firing for a number of years.  i use the clay and glazes that anyone else would.   i have not found any problems after i started spraying glaze instead of any other method.   i do not even spray the "accepted" way.   i can glaze a kiln load of my work in an afternoon.  it is an L&L kiln about 23x 27 (or so).  i always use the slow glaze that is built into the electronics.   i figure the kiln manufacturer knows more than i do about how to use the kiln to my advantage.
most of what i make is serving ware,  flat, not much higher than an inch or two and not difficult to make.   botanicals pressed into slabs and shaped using wood and foam rubber or pantyhose covered small bowls.   cracker trays and butterdishes.  they sell quickly and are so easy to make that i really do not do the things most throwers  do.  i can throw but at 82 my fingers do not have the same suppleness they did.  an afternoon of throwing might result in waking up to throbbing fingers that night.
the fun in what i make is the choice of botanicals, placement on the shape i use, lots of freeform stuff that dries inside old platters, bowls etc.    you might look at my photo albums .   click on my avatar and choose "my profile" and look for photos from 2016 holiday sale in november.   each of us has an album space available to show our work or an idea to share.  
if you want to try single firing the absolute RULE is   FIRE ONLY TOTALLY DRY PIECES, NOTHING THICK!
 
 

Yes, like Mea said once you remove the magnet on the outside the inside one falls away. If the inside glaze is soft then just drop a scrap of newsprint into the pot first and set the magnet on that.
Another point about why I use a twist tie with the inside magnet is so I can reach the magnet without touching the inside of the pot. Bend it shorter for short forms. For wide open forms like bowls just using the magnet bundle is enough. 
Use enough magnets to get a strong bond between the inside and outside magnet(s), needs to be strong enough to hold together while removing the pot from the glaze bucket (with the suction from glaze) but not so strong that they are difficult to remove.
Rare earth magnets are strong but they are fragile. I've tested ones from different suppliers, I have found there is a difference in the strength of them. They can break but are still useable. I have read that if you have a pacemaker then it's best not to use them. 
 

I’ve been using neodymium magnets as glazing tools too, thanks to @Min suggesting this to me several years ago. Can confirm that this is a game changer! I have my inside magnet wrapped in fabric held on by a rubber band. The fabric helps cushion the magnet so it doesn’t disturb the liner glaze, and the rubber band “stem” is like a handle. My outside magnet has a big eye bolt as a handle. 
I’ve learned to keep them stored on two different shelves, otherwise they will seek each other out and stick together, and it takes a lot of strength to pry them apart! 

Glazing tools and tips brought up in this thread, starting a new thread as this should probably be in the Studio Operations section.
This is how I use magnets when glazing, no tong marks, drips or finger marks on the glaze. It’s been a game changer for me with the pots I dip. Flat bottoms on pots work the best but you can do rounded bottoms, it’s just a bit less stable while dipping. 
- liner glaze the inside like usual
- rare earth magnet(s) wrapped in a scrap of plastic with twist tie inside the pot. twist tie is used as a handle. keep the twist tie below the rim of the pot
- another rare earth magnet(s) with a flat head bolt for a handle on outside of pot
- fishing magnet used for larger pots, they come with a handle so don't need a flat head bolt for a handle
-number of magnets needed determined by pot weight (and base thickness). I try to use just enough to be adequate to pull the pot from the glaze but not more or else they can be fiddly to remove. for tiny pots I use 1/2 pieces of broken magnets.
- hold the pot by the bolt and push the pot into glaze then lift it out. (rotate the pot slightly to have any excess glaze roll around the rim) 
- when the pot is dry enough to touch at base area turn it over and remove magnet(s) from either side. 20 seconds or so for most glazes. I hold the pot on the outside bottom of the pot when flipping over 
- you can slide the pot onto the edge of a counter while removing the outside magnet if you don’t want to wait for the glaze to dry enough to hold onto the pot, or stuff your hand inside the pot to move it to a ware board.
- when I first started glazing like this I got a couple blood blisters, don't pinch your fingers, those magnets are strong!!!! I use the ones from Lee Valley tools. (to separate them use an edge of a counter and push them apart)
Anyhow, that’s it, simple and it works. I tried to think of a way to market the magnet glazing but life got in the way.

Hi np.04,
Is your firing governed by a controller?
If you are able to set cones where they can be watched*, that might be a real help - you could start your cool down when the heat work is completed.
*be sure to wear kiln glasses against the harmful rays and any flying bits!

A cone temperature chart confirms that this is a real effect. A cone number relates to an amount of heat-work and the maximum temperature needed to achieve this depends on how fast the kiln is heating towards the end of the firing.
https://www.overglazes.com/PDF/Orton-Cone-Chart-C.pdf


Did you previously fire by observing the cone drop or just use it as record of the firing?

Yes definitely possible. So silica and alumina do not melt basically on their own below about 1600c/3000f. So they need flux to help melt at a lower temperature The fluxed reaction pretty much takes place in the last 100c of the firing, prior there is just not enough energy to get things going. So temperature and firing speed in the last 100c is super critical, to which PeterH has posted the Orton cone chart above.
As kiln elements age their power decreases and eventually they can’t make a reasonable final firing speed and things begin to over fire. The same goes for anything that slows down the firing such as worn elements AND a cold external firing temperature. In the end though -9c is cold but not that cold so likely the elements are fairly worn. How many firings are on them and to what cone do you routinely fire?
 
 
 
 

Ok I showed up at noon and others where walking thru house buying up stuff. Looks like a small amount of my work had sold . . But the tables where still stuffed.I told the fellow for me its all or nothing deal. I made a quik  rough list and  and down sized my offer to 450 $ cash. I said I have the boxes and paper and will take only my work as there was other ceramics mixed in especailly on the floor under tables (not in the photos)He took the offer which is about 16 mugs for me sales wise these days. I boxed it into 6 Banana boxes  full and dollyed it out feeling great. The womans sister spoke to me and said the lady (her sister) had a stroke and was in full time care now in North Caralina.I said she had the most work of any customer I ever knew  of and gave her my card to thank the sister . I have never met here as 99% of all the work was from a few outlets and they all had the price labels and cards inside of them. Not my own show price labels but those of my Eureka outlets. The largest amout of stuff was from a co-op organic market I pulled out of a year ago as I am slowing it down with a plan. I put a care and feeding tag in every pot  then and all those where still in every pot. Now I have a nearly a 35 cubic feet whole  kiln worth of new old stock. Its insane really. In my 50 years I never in my dreams would expect this to happen. I'm selling the stock twice this time without having to make or glaze or fire it.  Of couse prices have risen since I sold this  originally so I'm really ahead . I'm making 4 dinner plates for the friend who sent me the info last night. She really came thru for me.
There where two tables of pots  like the one photo  as well as a bunch on the floor
Just when you think you have seen or heard it all   -boom something new surfaces .

Finally got round to doing what has been suggested many times before.  Filled a pillow case with dried out clay, thin pieces mainly, and put pillowcase into bucket of water.
Left it for a week (community centre - only go there weekly).  Pulled it out, stood it in a bowl to drain.  Left it for another week.  Poured off excess water.  Left it for another week.
Took it out of pillow case this week, cut lumps off, handed out to class to use.  Perfect and little to no effort on my part - hurrah.
Can't believe how easy this was.  I usually reclaim in a bucket, and removing anything drier than slip has always been a nightmare. 
Started another pillowcase this week from the previous 4 weeks dried out clay.  This has changed my life.
Humidity is low indoors, and heating is on, which has helped with evaporation.  Might work a bit quicker in the summer.

Oh, we have a pugmill, but never enough to fill it.  and you can't empty them!

Oh, we have a pugmill, but never enough to fill it.  and you can't empty them!

Finally got round to doing what has been suggested many times before.  Filled a pillow case with dried out clay, thin pieces mainly, and put pillowcase into bucket of water.
Left it for a week (community centre - only go there weekly).  Pulled it out, stood it in a bowl to drain.  Left it for another week.  Poured off excess water.  Left it for another week.
Took it out of pillow case this week, cut lumps off, handed out to class to use.  Perfect and little to no effort on my part - hurrah.
Can't believe how easy this was.  I usually reclaim in a bucket, and removing anything drier than slip has always been a nightmare. 
Started another pillowcase this week from the previous 4 weeks dried out clay.  This has changed my life.
Humidity is low indoors, and heating is on, which has helped with evaporation.  Might work a bit quicker in the summer.

After my first failed attempt at building my own stands for firing jewelry, I've succeeded in fabricating new stands which held up to ^6 firing! The first time around, I made the stands with ^5 B-Mix and bisque fired them to ^04. They seemed solid enough, but when I fired the assembled stands, the weight of the jewelry caused the stands to sag, which, in turn, caused most of the jewelry pieces to run together and touch its neighbor. The melting glaze joined the pieces permanently. In the cases where the pieces were not co-joined, they were stuck to the stainless steel wire I used to string them because I drilled the mounting holes just big enough for the wire to fit AND I didn't clean the holes of glaze, thus fusing the pieces to the wire.
This time around, I added a strut to the B-Mix w/grog ^5 stands and fired them to ^6. I drilled the jewelry holes bigger and cleaned the holes of glaze. The stands held up to the firing and I had only 2 pieces stick to the wire but was able to break them loose without breaking the pieces. The photos show the first failed attempt, the second successful attempt, the layout of the stands, the assembled stands, and a selection of copper-toned pieces that I thought came out looking pretty darned good! (The penny is to show proportion.) In a number of the pieces, I was going for a raw, organic look with the rough edges which I think will look great as part of a necklace.

Finally got round to doing what has been suggested many times before.  Filled a pillow case with dried out clay, thin pieces mainly, and put pillowcase into bucket of water.
Left it for a week (community centre - only go there weekly).  Pulled it out, stood it in a bowl to drain.  Left it for another week.  Poured off excess water.  Left it for another week.
Took it out of pillow case this week, cut lumps off, handed out to class to use.  Perfect and little to no effort on my part - hurrah.
Can't believe how easy this was.  I usually reclaim in a bucket, and removing anything drier than slip has always been a nightmare. 
Started another pillowcase this week from the previous 4 weeks dried out clay.  This has changed my life.
Humidity is low indoors, and heating is on, which has helped with evaporation.  Might work a bit quicker in the summer.

I think its a all around bad idea. You do not eat off the stone. Why would you put food on that sealer.
You can as Min said have it tested but why bother its not a food sealer. Good money after bad in my mind-let us know what the results are when the lab report comes back.
 
 

Finally got round to doing what has been suggested many times before.  Filled a pillow case with dried out clay, thin pieces mainly, and put pillowcase into bucket of water.
Left it for a week (community centre - only go there weekly).  Pulled it out, stood it in a bowl to drain.  Left it for another week.  Poured off excess water.  Left it for another week.
Took it out of pillow case this week, cut lumps off, handed out to class to use.  Perfect and little to no effort on my part - hurrah.
Can't believe how easy this was.  I usually reclaim in a bucket, and removing anything drier than slip has always been a nightmare. 
Started another pillowcase this week from the previous 4 weeks dried out clay.  This has changed my life.
Humidity is low indoors, and heating is on, which has helped with evaporation.  Might work a bit quicker in the summer.

One of the best ways to reclaim when not having a pug mill!
 
best,
Pres

Finally got round to doing what has been suggested many times before.  Filled a pillow case with dried out clay, thin pieces mainly, and put pillowcase into bucket of water.
Left it for a week (community centre - only go there weekly).  Pulled it out, stood it in a bowl to drain.  Left it for another week.  Poured off excess water.  Left it for another week.
Took it out of pillow case this week, cut lumps off, handed out to class to use.  Perfect and little to no effort on my part - hurrah.
Can't believe how easy this was.  I usually reclaim in a bucket, and removing anything drier than slip has always been a nightmare. 
Started another pillowcase this week from the previous 4 weeks dried out clay.  This has changed my life.
Humidity is low indoors, and heating is on, which has helped with evaporation.  Might work a bit quicker in the summer.

Finally got round to doing what has been suggested many times before.  Filled a pillow case with dried out clay, thin pieces mainly, and put pillowcase into bucket of water.
Left it for a week (community centre - only go there weekly).  Pulled it out, stood it in a bowl to drain.  Left it for another week.  Poured off excess water.  Left it for another week.
Took it out of pillow case this week, cut lumps off, handed out to class to use.  Perfect and little to no effort on my part - hurrah.
Can't believe how easy this was.  I usually reclaim in a bucket, and removing anything drier than slip has always been a nightmare. 
Started another pillowcase this week from the previous 4 weeks dried out clay.  This has changed my life.
Humidity is low indoors, and heating is on, which has helped with evaporation.  Might work a bit quicker in the summer.

Fire Under The Oaks
3 Days 3 Extraordinary Instructors One Spectacular Event
February 10,11 & 12, 2023
Come join us for an exciting Alternative Firing Workshop at the Biloxi Center for Ceramics on the beautiful campus of the Ohr O’Keefe Museum of Art in historical Biloxi, MS.
Three legends of Southern Pottery:
Randy Brodnax of Marble Falls, TX Don Ellis of Farmington, NM Ron Wilson of San Antonio,TX Are joining us to provide 3 full days of instruction on a plethora of both traditional and modern alternative  firing techniques including:
Raku, naked raku, obvara, horse hair & feather, sagger firing, fuming with stannous & metal chlorides and interference mica techniques. Glow-worm wood fired cone 10 kiln firing.
You will also learn how to construct your own affordable downdraft barrel kiln.
Each hands on workshop attendee will spend a full day learning from each of our master potters over the three days and participate in firing your own bisqued pieces.
Lunch will be provided, as well as snacks & beverages during the day.
Registration

The Safety Data Sheet for it is here. Snippet of it below, you can see it contains water, fluoridated acrylic copolymer and a "trade secret" ingredient. To get it lab tested you need to give the lab the names of the ingredients you want it tested for unless you get a broad range test done which would be very expensive.
It isn't made for human consumption. You are a lawyer, I think you know the possible ramifications of using a product for other than it's intended use would be.

yes, babs, everything is getting heavier.   there is such a thing as gravity now, i never really noticed it until lately.   just brought home 500 pounds, packed like pres gets his, 50 pounds to the box.
i hijacked 2 neighbors going by and asked them to just set the boxes inside the bay window and i would put them underneath the shelf right there.  i dropped two of them and the helpful neighbors asked me to just get out of the way while they did it.

Finishing the bottom of a pot is a necessary step in the process, just like throwing and glazing, and all three steps are equally important to the success of the work. Finishing the bottom can be very involved like trimming a fancy raised foot, or it may be very simple like just rolling the foot on the table to smooth out the corner. Whatever method you choose, it needs to be done well and the results should enhance the pot. Too many people see trimming as an annoyance that has to be tolerated rather than mastered- everyone wants to put all their effort into mastering throwing. Mastering trimming  will make one a better potter just like mastering throwing and glazing, and to me that means mastering all aspects of trimming, including centering and anchoring your pots. The Giffin Grip works great for some types of pots, but not so much for others, so learning other techniques is absolutely necessary.
As I said in my original post, if you want to use a Giffin Grip then go for it. If it works for you, great, nobody is stopping you! But I do not allow them in my studio because it is my job as an instructor to lead my students to mastery, and that does not involve using a GG. And I can assure you that my students appreciate that and are making beautiful work despite my tyrannical methods. If you would like to open your own studio and rent Giffin Grips to your students, then by all means do it, and good luck.