Babs

I too have used shelf props but topped them with bits of broken shelf size of base of pot 

Hi Maria and welcome to the forum!
Is this the Turner's White recipe you used? If it is did you include the zirconium opacifier both in the past and with this current batch?

Article on Turner's white with some examples
It Slices, It Dices! Some Simple Glaze Tests Reveal a Ceramic Glaze That Can Do it All (well, almost)
https://ceramicartsnetwork.org/daily/article/It-Slices-It-Dices-Some-Simple-Glaze-Tests-Reveal-a-Ceramic-Glaze-That-Can-Do-it-All-well-almost
.. I notice it says under Colour Development
The second part of our project was to use Turner's White as a base, but just exclude the Zircopax (an opacifier).

My thoughts after reading that you can get the product on the Big river website.
Great to read that there is so much love and caring in our Community. 
 

@CharliesMomma, since you now know what was used another option would be to purchase another kit and make some test pieces with it.(just use something from around your house to make some little pieces with creases, maybe wrap them with saran wrap to get the creases) Wrap them up and leave them in tissue and see if they develop the same discolouration. If they do then finish drying them in the same way as your original pieces. Test those pieces with a quality plaster mildew/mold remover and leave them alone for as long as possible ( a year at least) then check for deterioration of those pieces. I would also contact a plaster restoration company if there is one near you and ask them about this, have them test the sample pieces.

I've refired old and dirty bisques many times before.  Clients send me pieces from all over the world that are decades old and been handled with oily hands, etc.  I refire these clean as a matter of standard procedure before I attempt any glazing so that I know the bisque is super clean before I proceed.  I agree, wash off what you can but if the clay may be porous at all, do NOT SOAK in water.  Water can dissolve salts and calcium out of your clay so merely wash up with a scrubby and a little soap, then rinse.  Set aside to dry.  I use a heater fan to help such pieces dry faster.
If you don't want to wait days to be sure the bisque is dry enough to fire, I go ahead and load it up into the kiln and fire on a low temp pre-soak for a couple of hours  before going ahead with the new bisque firing.   Cooks off any moisture left but do it slowly.  Obviously that is not an issue if the ware is fully vitrified  but I advise it for porous earthenware.
If after firing you are left with any dirty grey ghost marks you may sand the bisque to remove it if the glaze or underglaze you plan to apply isn't opaque enough to conceal it.  Alternatively you can also add a layer of opaque white underglaze and fire that before you proceed with color.

I agree with you on the jabs and removed them as this place is not for that -sorry as I degressed .I thank you for that reminder as well. Its all about clay nothing else .
Now on point Laguna has a 3 year supply at current consumption rates of Gretsly Borate. The mine is played out and this supply is all that will be ever.
In terms of The EPK shortage-yes it real and Laguna says it a weather supply mine/ chain issue. Its also happening to red clay and other materials this year due to  wacky weather issues they said. Storms and rain he said are so bad its really affected many products they use (we use in clay). One can assume as weather is a changing in many spots  on the planet this will only get worse.
The best policy is to stock up when you can.
 

Nice duck! Your grand kids did a great job.  I would give it 2 weeks before even thinking about firing. Go slow its too special to risk wrecking.  Good luck
Graybeard 

The article by Leela is nicely written, a great place to start if you've never done this before.
A couple pictures from an expedition to Sheep Mountain, about two hours from Anchorage. A massive landslide the day before deposited a thick layer of clay right by the roadside. It was happy timing, we had planned a long hike up the mountain to get to a bed of kaolin that's documented there. It was very plastic, threw like a dream, and didn't even shrink that much. Unfortunately this clay was nowhere close to pure kaolin. At cone 03 it softened and expanded into a puffy marshmallow like consistency. The bowl in the back held a sample at cone 6. Bubbly foam.

If this object is solid, I would use a drill bit to drill a series of holes in the bottom of it to allow for steam to escape. They don't have to be large, 1/4 inch or so maybe four or five where they would not be seen well space apart in the bottom.
 
Welcome to the forum!
 
best,
Pres

continued success with these large platters. Thanks again to all

MAGMA and CMC gum have some of the same qualities but they are not the same. 
Good chart here showing the qualities of many glaze suspenders and additives. What the chart doesn't show is how the glaze applies with CMC vs MAGMA when dipped. The latter doesn't  cause the drips/curtaining when used in dipping glazes.

Use a brush when washing dusty crevices. Leftover dust will interfere with the glaze adhesion. 

It might be interesting to try a crazing test on your test-tiles, such as

IWCT - 300F:Ice Water Crazing Test
https://digitalfire.com/test/iwct

If only to judge the effect of any changes you make to the recipe/firing.

Me too. I'll give it a shot with a line blend with some Turquoise stain. 
If I'm not so bloody rigid and just fire my ware at 1000 for this particular base, it's basically problem solved. And, it's a magical finish. 40 degrees (celcius) is literally what is separating me from where I am now and Leadless-Copper Valhalla. 
 

Aha! The clay body is a buff one, which means it’s both a thickness thing and a reaction with the iron in the clay. 
The simplified explanation is that whatever’s in honey flux, it behaves very much like a rutile blue glaze. The blue colour isn’t from a pigment, it’s from how light refracts back through the glaze and into your eyes. So thickness and the colour of the background the glaze is on will affect the end results. A thinner application and a lighter background will make this glaze look like it does on the Dover white clay example Lee posted above, and you can see what thickness did to your buff Anasazi. If you put this glaze on a red or black clay, you’d need only a very thin layer to get that same blue/white variegation effect that is on the chess piece in your last picture. 
If you want it to look like Lee‘s version, you’ll have to use a different clay, or apply a white slip/underglaze to your existing one. 
 
edited to add: given that the MSDS lists zinc in the materials, cooling time may be a factor as well. If the kiln pack was tighter on one firing than the other, that could also account for the difference. Zinc tends to allow glazes to stay more fluid for longer periods, giving them more time to either continue any chemical reactions or to just smooth out.

Thanks for the recommendations everyone! You saved me a bunch of time!  

I picked up a rubbing brick and it worked like a charm.  There's still some spots on the shelves that would require chiseling, but those are flush and I'll cover with kiln wash.  

I use a 6” carbide stone rubbing brick used to grind down concrete marks from molds.  It cleans up shelves quickly and costs about $16.  They are available in the concrete section of big box hardware stores.  Not sure about the black icky shelf but Im always up for a challenge because I fired kilns in a community center for years and have seen all sorts of stuff stuck to shelves.  If you want to toss it break it up in small pieces and use the clean bits as post spacers or under uncertain-maybe-might-run glazed work.

Post pictures and see if anyone can help. If you can, show the bottoms and any marks that might identify a maker. People often sign or stamp their work. Worth a shot.
Fun story, I was having dinner at a colleague’s house. He’s the science teacher, I’m the art teacher. In Anchorage, Alaska. He says, “You’re into ceramics, you might recognize these bowls,” as he loads one up with salad. “They’re made by someone named Shoji Hamada.”
So, he grew up in both England and Japan and his parents were great friends with Bernard Leach and Hamada. He just kept pulling out Hamada pots that his mom had given him while I was picking my jaw up off the floor. The kicker was when he pointed to a pot on his fireplace mantle and said, “That one’s a Peter Voulkos.” Sure as hell, a signed Voulkos, an early one, when still made pots that looked like pots.
”We use the pots because mom said that’s what he would have wanted. She loved pottery”
You just never know. 

Most if not all of your pieces will probably be fine. Some glaze melting will start at bisque temps, but shutting down at those temps usually doesn't cause any problems. Start it back up and fire to cone 5.

I think an important question is what other glaze is the Honey Flux being used with? It’s not supposed to be used alone. 

Speaking of old pillow cases, try hanging one in a frame, and add your slop clay to it. Let the water drain, then when stiffer. inside out the pillowcase to release the clay and wedge.
 
 
best,
Pres

Another thing you can do is cover the slab with a layer of fabric: an old sheet or pillowcase, size depending. 

The problem solutions I've tried out (and am happy with!), not new; some are used by many others, some are not popular at all.
For the second day of Wheel I class, I brought a large (large!) grout sponge to clean up with. From there, I cut up another sponge into purposed shapes/sizes (credit Bill van Gilder). The little round sponge that came with the tool kit saw enough use to eventually wear out (I didn't get a new one tho'!).
Leaving the work areas clean, that's required at the local JC ceramics lab. It's still a habit; I wipe down all.
That's one - likely a very popular re-use (grout sponges often have rounded corners, which I like better than car washing sponges; look for tight cell structure and soft feel).
Likely on the other end of the popular spectrum, I use a pointer tool for initial carving away of un-round bits when trimming.
Background, my hands don't alway work the way I'd like; I pretty much have to use both hands on the trimming tool, hence, no steadying finger on the ware.
Background ii, I expect the upper portion of the wares to be finished; when trimming, it's the bottom half (or third) that gets attention. I leave the ware on the bat until the top portion is approaching leather hard, then wire it off, which often leaves a step on the bottom.
Even with two hands, it's a challenge for me to round the ware with cutting tools. The point does not follow the contour of the work; it dives right in, boom, round, and boom, flat. There's the bottom and outside edge of my foot ring. From there, I go to the L (or J) shaped cutting tool.
If I were tempted (?) to go somewhere in the middle, perhaps the various marking, burnishing, and chattering methods...

This is a complete shot in the dark with no photos and not knowing much about what’s in the glaze. It’s described as creamy and honey at cone 5, then fluid and white at cone 6. Sensitive to temperature differences. Probably sensitive to application thickness. It makes me think temperature and cooling rate may have something to do with it. A kiln packed full will take longer to heat and cool slower than a light load, something to consider.
That said, I’m speculating. The SDS listed rutile and calcium, but I didn’t see any source of boron, which seems to be the magic combination to produce blue via rutile.