Magnolia Mud Research

The pot looks really thick where the blowout occurred. That to me means it was to damp for your firing cycle (to fast ). Moe  dry time and  less thick pot (more trimming)

I can only speak for my glazes and results but after I started doing a small hold at top for 10m (~2190-2200 depending on kiln load), a drop down to 2085 for 30m all of my glaze issues for the most part are good. I seem to get a nicer finish on both matte and glossy with the hold vs just going to peak temp. This is the digital fire drop and soak (no slow cool) schedule and I have never looked back.

For a large piece I would roll out a slab of the same clay as your sculpture is made from, make it about 1/4 - 3/8" thick then cut strips of it about 3/4" wide. Dry the strips between boards (or drywall pieces or whatever). When you go to fire your sculpture lay the strips down first, gaps between them, and sit your sculpture on them. (don't need to bisque fire them but make sure they are bone dry before firing and fire slowly) What you are trying to do is raise the piece off the shelf and allow air circulation underneath the piece to help even out the temperature.
Re slowing down between 1000F - 1100F both when heating and cooling, it's at approx 1060F that quartz inversion happens. As the quartz crystals change from an alpha crystal structure to a beta one there is a volume change of 1 - 2%, this can stress the clay and cause cracking / dunting. 
 

Also watch out - if your piece is on a base of some kind that is thick or wider than parts above it that are slimmer, you should stilt the piece to raise the bottom off of the floor of your kiln a little bit.  Uneven cooling can result after firing if the base retains a lot more heat due to contact with the thick kiln floor and the rest of the piece cools faster.  This can cause cracking or even dunting later well after firing.  If you do what Min suggested and slow down your cooling cycle by ramping it that will also help a lot to give the piece time to slowly equalize the heat throughout.  Kind of like the long heat cycle given to blown glass pieces so that it can relieve the stresses in the worked material.   As I fire a lot of horse pieces with very slim legs that are on thicker bases this can especially be a problem with the glassier porcelain clays or bone chinas.  I find it to be less of an issue with more porous clays like earthenware as they are less thermally conductive.

People don’t buy pottery for aesthetics. I mean they do, but they’re buying your “eye.” It’s possible to buy white rutile pottery in my grocery store for a fraction of what I can make it for. But they buy my pottery because they like my take on that theme. 
 

Most natural gas presures  for the home are 1/4 pound or 7 inchs on a manometer  .
That  works  fine for gas kilns as well. Just hook it up and start firing
If  you ever needed more pressure you would turn up the pressure at the main meter (which you will NOT need to do). The devices in your home stove ,water heater ,furnace etc all have presure devices built in, they regulate the presure to 1/4 lb.
You do not need any other device. Now propand is a whole different anamal.

@Kelly in AK, I used to be the same, thinner was the mantra, especially in front of students. However, my old self would have gasped at the weight of the floor vases I have made for my wife and some others, but they do not tip over very easily and support long strands and branches without a problem.
 
 
best,
Pres

There is old criticsm of certain aspects of glaze chemstyr as being overly complicated and a bit elitist - the UMF system in particular.
Some of the most sucessful potters I've known grew up on a healthy diet of 'melt and see'.  They wasted some time, energy and materials over time I imagine but we did just fine for our purposes.
There is obvious value in the UMF but please don't let the language muffle your curiosity.
 
 

@Bam2015 don’t let this thread overwhelm you too badly. If you want to zoom out far enough, no glaze will be as good as the day it was fired in a thousand years. They’ll all break down eventually.
While it’s possible to get really granular about the chemistry, it’s also worth noting that there’s also a pretty wide range of things that can be considered durable. The “good enough” threshold has at least some flex in it. And chemistry isn’t the only factor: the entire firing cycle is at work, as well as any interactions with the clay body itself. 
We use tools like Stull maps, glaze calc software or limit formulas to help reduce some empirical testing, but it doesn’t eliminate the need for at least some due diligence test tiles. And that holds true with commercial clear glazes too. At some point you have to pick a recipe to mix, apply it to a pot and find out.
 
 
 
 

The things being discussed here is are not necessary to good glaze formulation. I've been making durable glazes for 30 years without ever looking at a Stull chart or Katz's papers. Learning the basic of glaze formulation- fluxes, stabilizers, and glass formers- will serve you just fine, and allow for tweaking formulas to increase durability and adjust glaze fit for your clay body.
Commercial glazes are not necessarily any more durable. They all take testing as well. Clear glazes are generally quite safe if they're free of lead and cadmium, which most all glaze recipes being used nowadays are, and they don't have the heavy metals (colorants) in them that are likely to leach in a poorly formulated glaze. The benefits of mixing your own glazes are that they are much less expensive, and you can alter them as needed to fit the clay body you're using. If you know another potter that has a good clear glaze, by all means ask them for a recipe.

crushed up and screened soft brick can work nicefly in a flour sifter

Helmer works great as a flashing slip so I would just keep it on the outside myself where its seen and it costs more than epk

Just a few thoughts...I remembered the proper description of the diesel engine thing the company produced...they made diesel engine particulate filters.
Simply put the filters are these ceramic things, 3" wide by 14" long, that have a 1/4 radius cylinder shape, and have 99 little holes that trap diesel fuel particulate as the exhaust fumes pass through. The extruder that creates the holes is made up of 99 little tubes (I think?) that push through the clay and leave it with 99 little holes all the way through the 14" length. The holes were 1/16" if I recall. Truely amazing feat.
The extruder form was metal. And I think it was heated? (for lubrication perhaps?) Maybe this is the key to this situation. Rather than think of terms of plaster/cement molds think about heated metal molds? Extruded rather than cast? 

I know you said the pots were dried for several weeks and they were candled but when looking at the images this looks like a blowout from an air pocket that contained moisture within. This isn't the same as an air bubble.
My hunch is that when you were centering and opening up the mass of clay there was some clay pushed down that overlapped the existing clay and formed a pocket. If the clay contains a fair amount of ball clay or other fine particle material and was also heavily ribbed over this would exacerbate the problem of allowing the moisture to escape. Think about a fully enclosed form, yes we can fire them without them exploding or having blowouts but it takes far longer for them to reach a bone dry state right the way through the clay wall than the same form with an opening in it. No clue what the weather and humidity is like in Northwest Arkansas, perhaps it's a contributing factor, don't know.
 

Lots of great discussion here, but we still don't know what the blowouts look like, where they were on the piece, etc. OP has abandoned us. Personally, I've never considered compression to be the cause for blowouts. They are typically caused by foreign bodies in the clay or moisture. I don't see why compression, platelets alignment, etc, would cause a section to violently separate from the piece.

If you have a look at the Safety Data Sheet (SDS) you can get a rough idea of some of what is in the glaze. For Laguna's Tangerine Ice a snippet from the SDS shows this:

Doesn't include colourants and I think they have omitted whatever material is supplying boron but you can see from the first line there is a lithium material, this could well be spodumene. There is also silica plus calcium carbonate plus kaolin plus bentonite. From looking at the glaze plus looking at the components above I would hazard a guess this is going to be a microcrystalline glaze caused by a high level of calcium (ie a calcium matte or semi-matte) and that is what is causing the dappled look. I'm going to hazard another guess and think there is also titanium oxide in it also, perhaps from titanium dioxide or rutile. Is this glaze glossy if fast cooled and more opaque and dappled/mottled when slow cooled?

Hulk/Tom,
When people throw pots they generally lubricate the clay with water. (So the clay slides between their fingers.) The water will often collect at the bottom of the form.
If the thrower repeatedly tries to "improve" the form they may leave a lot of water at the base of the piece. If they don't keep this accumulated water to a minimum the clay may become over saturated and separate once the piece dries/is fired.
An easy way to rule this out is to throw the form quickly and keep the water to a minimum. If this type of cracking persists it may be a clay formula problem.
Rather than try to throw the perfect shape, and over work the clay, throw a pot as best you can, in a shorter amount of time, and then trim it to your desired shape. 
 

I've no practical knowledge, so treat this all a here-say
I'm interested in how you get on, but ...
- I don't think either bones -- or seashells -- will survive high firing sufficiently intact to act as a stilt.
- I doubt that bones will help form a "glaze" in the same way that seashells do.
Firstly I think shells are used as a separator between the pot and clay wadding placed inside the shell. Shells seem a much better shape for this than most bones.
Effective Side Firing
https://ceramicartsnetwork.org/pottery-making-illustrated/pottery-making-illustrated-article/Effective-Side-Firing#
While wadding is traditionally only used in atmospheric kilns to prevent pots from sticking to the shelves, it is necessary for side firing in electric kilns.  Sea shells turn to powder (calcium oxide) during the firing, and will not support the weight of a pot.  Using wads under the shells prevents the pot from falling onto the drip tray and sticking to it.
Secondly the chemistry is different, perhaps critically so.
Shells in Ceramics
https://www.weloveclay.com/read/53007/53007/
Why then were shells not adopted more widely? Australian wood fire potter Owen Rye has pointed out that though ancient potters were keen observers of their craft, none could have understood or intuited the science of shell use. The shells themselves are formed from calcium carbonate which, when heated, converts to calcium oxide or ‘quick lime’, a powerful flux. In isolation, calcium is one of the most refractory oxides, only melting at 2572˚C+. But combine that calcium with alumina and silica and you have what is known as a ‘eutectic’ – a combination of oxides that melt at a lower temperature than they would on their own (in this case, a much more manageable 1170˚C).
Why then were shells not adopted more widely? Australian wood fire potter Owen Rye has pointed out that though ancient potters were keen observers of their craft, none could have understood or intuited the science of shell use. The shells themselves are formed from calcium carbonate which, when heated, converts to calcium oxide or ‘quick lime’, a powerful flux. In isolation, calcium is one of the most refractory oxides, only melting at 2572˚C+. But combine that calcium with alumina and silica and you have what is known as a ‘eutectic’ – a combination of oxides that melt at a lower temperature than they would on their own (in this case, a much more manageable 1170˚C).
All this means that on the interface between shell and pot there is a melt that leaves a shell-like scar on the surface of the clay. As the shells are stuffed with clay to prevent them from collapsing, the same happens on the inside. The core of the shell remains pure calcium, which is dry, friable, expands when wet and can be easily removed after the firing. An aesthetic bonus of using seashells is that they contain small quantities of salt. During the firing, this salt can volatilise, leaving a subtle halo of salmon pink or orange on lighter coloured clay bodies.
 
Shells decompose into calcium oxide, bone eventually decomposes to a mixture of calcium oxide and phosphorous pentoxide, which may well prevent a suitable eutectic forming. Also bone ash tends to retain some of its structure, probably making both oxides less available for forming a "glaze".
https://en.wikipedia.org/wiki/Bone_ash
Bone ash is a white material produced by the calcination of bones. Typical bone ash consists of about 55.82% calcium oxide, 42.39% phosphorus pentoxide, and 1.79% water.[clarification needed] The exact composition of these compounds varies depending upon the type of bones being used, but generally the formula for bone ash is Ca5(OH)(PO4)3. Bone ash usually has a density around 3.10 g/mL and a melting point of 1670 °C (3038 °F). Most bones retain their cellular structure through calcination.
 
 

Chris Campbell, one of our members has been inactive here for some time.   she makes all kinds of colors from pale yellow and pink to darker colors.   check her albums for some examples of her fabulous work with shading and blending.   computer illiterate here, maybe you can see her previous posts.  look under chris campbell pottery for several articles and photos of her work.

Some people find it helps to dip pots in water very briefly before glazing if the body is grogged. Theory is the water expels any tiny air pockets cause by the grog so when the pot is dipped in glaze there isn’t trapped  air which in turn can cause pinholes in the glaze firing. If the body is burnished with a rib after trimming this is reduced.

Don’t get too hung up on specific SG numbers. The number that works is the one that gets the right application of glaze YOU want on your pot, and that might be different than what someone else recommends. The 1.4 mark is a rough starting point, kind of like seasonings in a recipe. Some people will want more, some people will want less. 
First, water is the easiest thing to adjust in a glaze, and adding things like epsom or darvan to adjust how a glaze flows should be done only after you’ve determined it’s really necessary for getting the right glaze application. If the bucket has a layer of glaze materials in the bottom within 5 minutes of mixing, pulling out the epsom salt solution is the right thing to do. 
Adding epsom salts will flocculate a glaze, or make it gel slightly. This is why the glaze now seems thicker than it did, and it may leave a more generous layer on the pot than the same 3 second dip would without the flocculation. You might notice on some glazes it will start to crack while drying, potentially causing crawling in the kiln. And yes, it will also slow your drying time. That slowed drying can help smooth out application based drip marks. If your glaze is one that might be subject to crawling due to application, adding water will help resolve that. But know that adding water to a glaze that’s already flocculated will further delay drying. It may mean you have to adjust your workflow to allow for that, but it’s worth it if it means the glaze goes on the pot nicely. 
Another question worth asking is whether or not any of your ingredients are soluble in the bucket over time. It’s usually more of a problem with boron containing materials, but some feldspars can be subject to this as well. Solubles can affect glaze application if they cause additional gelling. 

I refire a few pots everty fire to cone 10 and never used cmc for that process. If you want more glaze on pot warm the pot and then dip or pour the glaze on a  warm pot let dry. refire .
no need for gum

I have a whole two acre lot with a stream that has cut through it.  There are no cracks in either bowl , they ring nicely. I dipped the rim of the left hand bowl in an ash glaze.  the brown cube was my melt test fired on a cookie to cone 10.

If you run a bit of 220 grit wet/dry carbide sandpaper (I get mine at Canadian Tire), it should take off stubborn alumina remnants. If you feel fancy, you can tack some to a bat and make a quick and dirty polishing wheel. 

If no need to be double sided - conventional masking tape? There are a variety of adhesives, fine line, etc, to choose from and they are available in different widths.