LeeU

I'm big on Serendipity...I've just spent some time yesterday and today updating my Hidden Masks text in the Gallery, and adding to the Aesthetics and Philosophy Forum topic "What Was I Thinking?", which is about....what were you thinking? All of which addresses the QotW re a certain mentality or emotional state tied to engaging with clay.
I assume I may take the liberty of adding  clay artists, for those who may not self-descibe as being potters.  I was once a potter, and while I did some great mugs-truly nice-and decent small bowls, most of my work is sculptural/functional. Some of the techniques, best practices craftmanship, and motivational approach might differ, but I figure clay is clay and working with clay is working with clay, and the drive to create is the drive to create, so I feel free to pipe up.
I did a search: Googled personality types of potters. The 1st hit was https://www.careerexplorer.com/careers/potter/personality/  Every subsequent hit was all about Harry P.
I'll leave speculation, or evidence-based, valid/reliable research results, on potters' personality attributes (or diagnoses LOL) to others. My 2-cents worth is that we Clay People may  comprise a kind of social strata-using the term loosly- via a commonality of emotional/mentality internal/external world views, but I have no clue as to what those might be. Fun topic!
 

I'm big on Serendipity...I've just spent some time yesterday and today updating my Hidden Masks text in the Gallery, and adding to the Aesthetics and Philosophy Forum topic "What Was I Thinking?", which is about....what were you thinking? All of which addresses the QotW re a certain mentality or emotional state tied to engaging with clay.
I assume I may take the liberty of adding  clay artists, for those who may not self-descibe as being potters.  I was once a potter, and while I did some great mugs-truly nice-and decent small bowls, most of my work is sculptural/functional. Some of the techniques, best practices craftmanship, and motivational approach might differ, but I figure clay is clay and working with clay is working with clay, and the drive to create is the drive to create, so I feel free to pipe up.
I did a search: Googled personality types of potters. The 1st hit was https://www.careerexplorer.com/careers/potter/personality/  Every subsequent hit was all about Harry P.
I'll leave speculation, or evidence-based, valid/reliable research results, on potters' personality attributes (or diagnoses LOL) to others. My 2-cents worth is that we Clay People may  comprise a kind of social strata-using the term loosly- via a commonality of emotional/mentality internal/external world views, but I have no clue as to what those might be. Fun topic!
 

I'm big on Serendipity...I've just spent some time yesterday and today updating my Hidden Masks text in the Gallery, and adding to the Aesthetics and Philosophy Forum topic "What Was I Thinking?", which is about....what were you thinking? All of which addresses the QotW re a certain mentality or emotional state tied to engaging with clay.
I assume I may take the liberty of adding  clay artists, for those who may not self-descibe as being potters.  I was once a potter, and while I did some great mugs-truly nice-and decent small bowls, most of my work is sculptural/functional. Some of the techniques, best practices craftmanship, and motivational approach might differ, but I figure clay is clay and working with clay is working with clay, and the drive to create is the drive to create, so I feel free to pipe up.
I did a search: Googled personality types of potters. The 1st hit was https://www.careerexplorer.com/careers/potter/personality/  Every subsequent hit was all about Harry P.
I'll leave speculation, or evidence-based, valid/reliable research results, on potters' personality attributes (or diagnoses LOL) to others. My 2-cents worth is that we Clay People may  comprise a kind of social strata-using the term loosly- via a commonality of emotional/mentality internal/external world views, but I have no clue as to what those might be. Fun topic!
 

I recently scored 4 lovely small dishes by Maureen Mills, in her very distinctive surface decoration "signature" designs, sold as "seconds" (due to things that no one not familiar with the intracacies of ceramics would ever notice, much less care about), for a delightful fraction of what "perfection" would cost. As the purchaser, it is great to be able to "afford"  someone's work that I would not be able to justify buying, within my tightly controlled budget! 
 
 

Better imo to apply underglaze when leatherhard, then glaze when bonedry , dry and fire through to glaze maturity.
Pots turn out just fine.
@oldlady single fires her pots perhaps she will chip in here.
Quite comon , really. I learned the orocess and came uo caling it Raw Glazing, there are other names around.
 

I recently scored 4 lovely small dishes by Maureen Mills, in her very distinctive surface decoration "signature" designs, sold as "seconds" (due to things that no one not familiar with the intracacies of ceramics would ever notice, much less care about), for a delightful fraction of what "perfection" would cost. As the purchaser, it is great to be able to "afford"  someone's work that I would not be able to justify buying, within my tightly controlled budget! 
 
 

I find Coyote's cone 6 White MBG023, when applied as Neil described,  to look like a glossy white mug you might get at Target. I also find that Stroke & Coat is not that great for mid-fire and the results are not always consistent w/what the labeling says the 05 will look like at 5. 

I recently scored 4 lovely small dishes by Maureen Mills, in her very distinctive surface decoration "signature" designs, sold as "seconds" (due to things that no one not familiar with the intracacies of ceramics would ever notice, much less care about), for a delightful fraction of what "perfection" would cost. As the purchaser, it is great to be able to "afford"  someone's work that I would not be able to justify buying, within my tightly controlled budget! 
 
 

I recently scored 4 lovely small dishes by Maureen Mills, in her very distinctive surface decoration "signature" designs, sold as "seconds" (due to things that no one not familiar with the intracacies of ceramics would ever notice, much less care about), for a delightful fraction of what "perfection" would cost. As the purchaser, it is great to be able to "afford"  someone's work that I would not be able to justify buying, within my tightly controlled budget! 
 
 

I do sell 2nds; pots that have tiny flaws that in no way effect the use of the pots. Things like slightly out of round pots (that are meant to be round) or glazing that isn't quite what I wanted. Definitely no cracks or chips. During summer Farmer's Markets I will put out a basket of clearance or 2nd best pots. This basket of pots isn't on a main table, it's off to the side on a small stool so not too obtrusive. Just about everyone asks why a pot is in my clearance / 2nd best basket, it's usually hard to spot why they are there. Hammer for anything I wouldn't want coming back and biting me. 
Thanks for posting my question Pres.
 

Another product you can use is a latex resist. Brush 3 coats on the bisque where you want the lava glaze then when dry glaze the pot in your other glaze. Peel off the resist and brush your lava glaze on. (Michaels carries this brand and often have 40% off coupons)
 

in case anyone wants to try bab's suggestion about carpet, be sure to use something from the thin but strong commercial stuff.   you do not even need wax if you do foot rings on the wet carpet, just slide the whole piece across the carpet,  the excess glaze will wash off instantly.  keep it pretty clean, especially if the glaze is a dark one.

Yes, you have a wide firing range clay so I would be surprized if fully vitrified at lower temp of range. You may think of changing your clay into the future.
clay and glaze maturing at Cone 6 or 7 would be a more economic and popular firing range. Google Midfiring glazes.
Bisque firing is low at 950degC ,go for  Cone 06, 1000degC ,  becoming more popular, cone 04, 1040 deg C.

The pottery shop most associated with this process is Dock 6. Kerry Brooks is the potter and she applied this process to coasters as well. She spent a year, or two, developing the process and the glazes that go with it. 
Again, she spent a year, OR TWO, developing this and I know she had a lot of failures. (Her studio/shop is a few miles from mine. I know she experimented with glazes, with firing temperatures, and with types of glass.)
Once she found success technically she found success in the marketplace. (Anthroplogie ordered 1000's.) 
Having seen failed experiments with coke bottles, in high school and college, I have never felt inclined to attempt anything like this. She found the sweet spot and her coasters really are a thing of beauty.

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

My way of wording the same info that @Callie Beller Diesel and @Roberta12 have said is:
We have enough problems getting clay and glaze that are sold as compatible, to be compatible, without adding an ingredient that is scientifically not compatible.
You wouldn't dream of putting diesel fuel into a petrol-engined car (or vice-versa), so why would you want to mix clay and glass. 
Petrol and diesel both come from crude oil, but are not compatible.  Glaze and glass may both contain silica, but they are also incompatible.

Know that despite how the tone of this might come across, I do sympathize with your ruined project. I mean none of this as shaming, only as information.
You have a relatively wide piece compared to the thickness, no foot rim, a very thin cross section and you glazed only the inside and the top of the rim. You don’t state it, but I’m  going to guess that the glaze layer was a comparable thickness to the cross section of the clay. That alone can be a solid recipe for dunting, even if you haven’t had previous problems with that glaze. That scenario can actually a way to set up a stress test for clay glaze compatibility. 
Add to that chunks of glass of unknown providence, which,  as mentioned above has a VERY different COE than either your glaze or your clay, and fired it far past the maturation point of the glass. I’m not at all surprised these coasters pulled themselves apart with some authority. 
It is, and always will be my opinion that it is ill advised to combine chunks of “found”  glass and ceramic material, ESPECIALLY in functional items. I have stronger words for people who teach this as a beginner project. I know lots of people do it, but it’s still a bad idea. You have unfortunately found a perfect storm example of why.
I do concede in that other thread that there are some circumstances where combining clay and glass do work, or where cullet is included as a glaze ingredient. But to make it work properly requires a very strong technical understanding of the differences between clay, glaze and glass. I will forever disagree strongly with anyone who just melts glass into the bottom of a clay dish. 
If you want some nice coasters to be able to gift for Christmas, even the most technically broken glaze would be a better option than glass. This would be a lovely opportunity to go on glazy, and test out some of those fun, runny zinc glazes that make crystals. I saw today that Birdie Boone and Osa Atoe are working together on just such an example. You could get some really fun effects with none of the headaches of using glass. If you’ve never mixed a glaze before, this is a very simple recipe, and would be a good place to start. Some of the ingredients are a little more expensive, but you probably don’t need large quantities, so it’s still pretty affordable. 
 
 

Firing glass on clay has come up a few times on the forum. General consensus of forum members is this isn't a good idea. Several threads on this topic, link below to one of them.
Don't think this would have been why. Reason why the melted glass has craze / crackle patterning is because the glass expands and shrinks at a vastly different rate than a claybody. COE or CTE (coefficient of thermal expansion), same thing, different name.  Sounds like with your original coasters the glass was much thinner than the ones that shattered in your latest firing. This doesn't mean it's safe practice to just put the glass on more thinly, still subject to stresses and the risk of slivers of glass dislodging. 
 

Ok if you read my post on buying back over $3500 new unused pottery from a horders estate sale for $450 then you know how starnge and rare that might be.
well lighning strikes again on that front
Today the day after Christmas at 4 pm I was bookkeeping on the desktop on a very rainy windy day. The phone rings and its the estate sale guy from 3 weeks ago. They found three more large boxes of my pottery and they need to get it gone. He says $100 for it all and you have to pick it up today. I had sanitized/reorganized my van on the only dry day Xmas afterr stuffing it full from taking xmas booth down xmas eve. I Jumped in and drove the 35 minutes back to that house. Last time it was jambed full-this time thay has a box moving trck and all that was left in the whole house was my pottery that they just found in 3 boxed in a hidden space in large kitchen under a counter back water area.  My guess is 1-2 k worth of stuff.I'll go thru it in a few days. Just like last time all new all still with sales tags on bottoms. I found out that this person bought my pots wrapped them and boxed them and put them away like xmas ornaments -all 5 k worth. She may have been my best customer-well its a toss up as another from the east coast who runs a private jet rental service may have her beat ? Hard to say as she bought dinnerware sets and lots of st=uff over time where as this lady bought it all in 3 years from one organic market before I quit them.
When I left the house a hour ago it was 100% empty of all contents-I drove home in disbelieve as Santa Extended xmas one more day at least to me
Merry xmas and Happy Holidays from Linda and Mark

I use the E6000 all the time for doing different things w/my cone 6 bodies--I like that in addition to clear, I can also get it in black, and the black does not fade over time.

Yep yep yep! Too many people don't plan for retirement, have no hobbies, and drop dead shortly after. Don't be "that guy".  Thankfully, I think we all know Mark is safe! I would still be happily, tho compulsively,  working my career in  state public behavioral health services (40 yr/2 states-clinical to program design to mgmnt. to funding development etc.) if I hadn't been a bad girl & joined the whistle blowers disclosing to the feds some very serious corrupt practices w/serious consequences to those we were supposed to serve. That got the state put under DOJ litigation and got me targeted to be forced out before I could be vested in the retirement. I fought back & prevailed, but knew it was in my best interest to retire the minute I was eligble. That said, while I grieved the loss of my work life, it turned out to be the best decision I ever made. I'm 75 now and that was 8 years ago. I lost a lot of stress, gained a lot of quality time, and am so happy that right now my kiln is cooling down, full of goodies, incl. some experiments.

I don't have a lot of other people's work-don't get around much & don't have the spendoolies. I like meeting clay artists and then may get a piece they've made. My little collection includes  (from the top left) Andy Hampton's cosmic tea dust mug, a nice box that holds my collection of fortune cookie slips, and a  tasty shallow  square catchall. Andy is the president of the NH Potters Guild and who I got to do a raku firing with. Then there is  Maureen Mills' little willow vase-she was the director of the NH Institute of Art's Ceramic Dept. and author of Surface Design for Ceramics (Lark); the next mug is by her partner, slip trail master Steven Zoldak-I got the mug at their studio during the recent Portland Art Tour. The small plate is one of  Maureen's "seconds" and  shows off her signature design w/implied text. The 5 lovely tiny vessels are by Joseph Painted Bear, who I met online. The tiny vase is by Karen Orsillo, who specializes in the Japanese technique of neriage. I met Karen at the NHIA anagama firings at the Sharon Art Center. Last, the gorgeous cacao pod, glazed in Palladium, is by a South Afrikan artist whose name escapes me now- met her in an online ceramics group. Then, since I couldn't afford one of John Baymore's pieces (John & students built the huge anagama kiln at the Sharon Art Center and of course he is well known to some in these Forums) I got the next best thing: I carried off one of his cone holders from a firing that hit  2400 f, ^12.
Update: I happened to re-read my post and noticed that the auto-censor has changed my text! "Then there is Maureen Mill's little willow vase..." Nuh uh...I did not write "little willow vase". What I wrote was the correct description of her slip-trailed piece, which is a  "little p--ssy willow vase".  I'd laugh if it weren't so sad.
 

Yep yep yep! Too many people don't plan for retirement, have no hobbies, and drop dead shortly after. Don't be "that guy".  Thankfully, I think we all know Mark is safe! I would still be happily, tho compulsively,  working my career in  state public behavioral health services (40 yr/2 states-clinical to program design to mgmnt. to funding development etc.) if I hadn't been a bad girl & joined the whistle blowers disclosing to the feds some very serious corrupt practices w/serious consequences to those we were supposed to serve. That got the state put under DOJ litigation and got me targeted to be forced out before I could be vested in the retirement. I fought back & prevailed, but knew it was in my best interest to retire the minute I was eligble. That said, while I grieved the loss of my work life, it turned out to be the best decision I ever made. I'm 75 now and that was 8 years ago. I lost a lot of stress, gained a lot of quality time, and am so happy that right now my kiln is cooling down, full of goodies, incl. some experiments.

Ive used portland cement as a glaze for many years.  Mixing a small amount at a time and using it within an hour works best.  I then fire it to c10 and it looks quite similar to a runny ash glaze.  Portland is comprised of lime, magnesium, iron ox, and silica.
Like Callie said its not something you want to mix alot of because it sets fairly fast.
 

From very cold/snow bound Minneapolis:
You have two options: 1) find a matte glaze that works for you OR 2) simply leave your piece unglazed and use underglazes. 
1: white color, in a glaze, is achieved by using a white color or opacifier.  Zircopax is both. It's also cheap. It does, however, have a slight ivory color to it. That it why its often coupled with a truely white material, Mason Stain White 6700 or tin oxide. The Mason Stain is about 2x the cost of zircopax and tin oxide is on par with cobalt these days. (very expensive) Both of these additives are a bit "whiter" than zirco (its subjective I would say) but owing to the expense are usually used to boost the zirco and not used outright. Something like 8% zircopax and 2% 6700 or tin could be a good starting point.
2: the Amaco underglazes, fired to glaze temps, would give you a very DRY surface if thats what you're looking for. The LUG version is more zircopax like, in appearance, and the Velvet version is a much colder white. Apply three coats, with a brush, and you should have a nice opaque color.  (I usually like to thin the first coat so it brushes smoothly.)