Min

I rarely need to level the base of a pot, if the pot has a foot ring (most om mine do) I don't try and level the entire base. I trim as usual then when I have the foot ring trimmed to width I trim a bevel into both the inside and outside of it then just use a loop tool to cut off the tip of it. Since it's just a very small amount of clay getting cut off it's easy to hold the tool level to do this.

 

Do you know what the specific gravity of the glaze is that you did the one dip of? How long did you did it for? Have you tried a much thinner coat of the same glaze?
Amaco does publish a colour chart with all their Velvet underglazes fired to 05, 5 and cone 10. If you scroll down to the blacks it looks like both the Jet and Velour Blacks survived cone 10. From the little inset blurb about clay and glazes used it appears that HF9 was used on both the cone 5 and cone 10 samples. If you try this commercial glaze please do check with Amaco on this as this is actually a cone 5 glaze.
https://cdn.shopify.com/s/files/1/1023/7667/files/Velvets_Underglaze_all_temps_brochure.pdf 

Nothing to do with the make of the kiln but I would suggest taking those shelves and posts off the lid of the kiln. Lids are expensive to replace if they crack.

Nothing to do with the make of the kiln but I would suggest taking those shelves and posts off the lid of the kiln. Lids are expensive to replace if they crack.

Nothing to do with the make of the kiln but I would suggest taking those shelves and posts off the lid of the kiln. Lids are expensive to replace if they crack.

Hi Henry and welcome to the forum.
Since you are in the countryside then zoning/regulations for a gas kiln might not be a problem but it's something I would look into, also if you have home insurance I would look into that aspect also.
Do you have someone or somewhere that could walk you through firing with gas?

I have made several vase forms that have 8-10 inch bases, and some bowls that have 12-14 inch bases. Presently I use a bat covered with a felt type rug with rubber backing. Using the wheel running slowly, with some dampness on the rug I can clean the surface of a foot ringed of flat form quite easily. The larger the bat the bigger the form can be covered. Two people holding the form should be able to make it work pretty easily using the weight of the form against the covered bat with the hands of the two individuals holding it steady. I use the same technique to clean the bottoms of chalices and patens for communion sets.
 
 
best,
Pres

Or mica perhaps?

Or mica perhaps?

Iron and manganese don’t sound like sparkles. Could they be referring to pyrites? I wedged vermiculite into my cone pad clay for quicker drying and less shrinkage. The sparkly surfaces of the pyrites survived low firings. 

A gas kiln comes with a bunch more disappointment and depending on how along you are it can be a bit demoralizing to find failure after failure.
That being said it's totally worth it if you can get past the initial, sometimes lengthy learning and trouble-shooting process.
Bisque is more even in an electric kiln but that not to say it can't be done well enough in a gas kiln.
If you are comitted and have deep pockets and miles of patience with yourself and your materials jumping in the deep end would be fun as heck.
One of the biggest 'buts' here, for me, is cost.
A proper gas kiln project is a money pit, even if you don't make any mistakes.
A small design will get you thinking though. You can start collecting the bits that will work to build a small kiln as well as someting more substantial.
I know folks who have been planning and collecting for going on a decade. For them it's something similar to building a house or boat - very much a labour of love.
If you are determined to high-fire in an elctric kiln  consider shifting to cone 9. The energy required to go from 9 to 10 is substantial. Cone 8 can work too but the list of feasible material begins to narrow.

If you want to do cone 10, you really want a gas kiln. You can do cone 10 in some electric kilns, but it's hard on the elements and not a great long term approach.
You might take a look at a gas kiln conversion called TDI Downdraft Kiln Conversion. There is a book on Amazon on how to construct it and how to fire it. There is a friendly FB group that can handle questions. I have one and can do cone 10 in five hours. I run it using two 20 gallon propane tanks. The first link below is a website by the creator of the TDI. The book has good info that can be generally informative on burners and firing even if you decide to go with a different gas kiln.
http://www.sebastianmarkblog.com/2018/07/gas-kiln-conversion-downdraft.html
https://www.facebook.com/groups/4124895130900261/?ref=share&mibextid=NSMWBT
https://www.amazon.com/Downdraft-Kiln-Conversion-Boris-Robinson/dp/B084DH88GH
 

Hi and welcome to the forum.
Just to clarify you are slurry mixing the slaked dry clay and including throwing water? If this is the case then adding some more plastic materials can fix this but I would test the reclaimed batch for absorption in case it also needs a top up of flux.
For slurry mixing adding a 2-3 percent of bentonite (by dry weight) will get it back to being plastic. Easiest way to get the bentonite to mix with the clay slurry is to put the dry bentonite into a  container of super hot tap water then whiz it up with a hand/stick blender for 10 minutes of so. It will turn into a very thick sludge, add enough water to make it like yogurt consistancy then add it to your clay slurry and use a drill with a jiffy mixer attachment (or similar) and whiz everything together. Tony Hansen from Digitalfire recommends dry mixing the bentonite with ball clay at a 1:1 ratio and using that. I haven't done this so can't comment on how well it works but basically doing the same thing.
If you already have a batch of processed reclaim then try wedging in about 20% new clay, this might be enough to bring it back to a workable condition.
BTW it is common to use nepheline syenite as a body flux.

I was recently asked about a pouring box for mold making. Here are two versions I use in the studio.  The image with the bulbous object is my main pouring box. The pieces are 3/4" plywood cut into 5"x15" boards. I then screwed 1"x1" strips onto the ends which provide a lip for the small "C" clamps. Very quick and easy to assemble a box in any dimension.
The second image shows another box variation that I use often for flat castings. The sides of the box are 2"x2" pieces of pine. (In his case I also used some 1"x2" strips.) The 2x2 pieces are labeled as "turning blanks" and come in a variety of wood types.  (Woodworkers use them to make stairway balusters.) Because they are square and stocky they don't need much bracing other than a little clay at their base. 
The mold on the left I free formed and did not use the box to limit the plaster. (I shaped it by hand.) The mold on the right I filled the box with plaster and then ran a straight edge along the tops of the wood pieces which resulted in a mold that was evenly thick. 
 

If you calcine alumina hydrate to drive off the H2O you will be left with alumina oxide.  (approx 35% LOI from it) Whether or not the mesh size is different I don't know. I found a pdf with mesh size of various aluminas here if you want to compare it to your alumina hydrate. If you don't calcine it there might be issues with both the glaze lay down and/or gassing off (plus the obvious difference of adjusting the recipe to allow for the LOI if you don't calcine it).

Since you are not too far away, here are a couple options.  About 10 years ago I convinced Alsey (a hard brick manufacturer in Illinois) to sell me three pallets of "seconds" for a significantly reduced price.  When they arrived they looked perfect to me and have done well in my wood kiln.  These were super duty bricks.  I think they were not really seconds and they were just being nice.  They normally crush up any rejects as grog in future batches.  https://www.alsey.com/
One other option: There was a second-hand refractory store near St. Louis that closed a few years ago.  A local guy that makes an occasional pizza oven bought all the remaining inventory he could move.  I bought a large load of 4x3x9" really nice bricks for only around $1/brick just a few months ago.  He probably still has a large inventory, particularly of large and odd-shaped bricks.  I can try to contact him if you are interested.  Would be a bit of a drive though.

I don’t know about other lustres, but gold and white gold are made of those actual materials, and don’t tarnish.
Some raku glazes that contain a lot of copper can be prone to reoxidizing over time. Usually folks will coat pieces like that with spray varnish or similar. I think it could work for Palladium. 

@AndreaK, lowfire and earthenware clay has been used for centuries around the world for domestic ware. How durable this particular  body is would have to be tested, I know some of the lowfire talc bodies were very weak. In North America  many potters have gravitated to midrange for various reasons, one of which is it's possible to have wares that don't leak or overheat in the microwave even if the glaze has crazing or pinholes and it's fine to leave the bottom of the pots unglazed. For lowfire (including earthenware for this conversation) in order for the ware to not weep / leak when used for mugs etc it is necessary to completely glaze the pot. (I do know someone who uses terra sig on the foot but that's another topic). A huge advantage of using lowfire / earthenware is the energy savings when glaze firing and the wear and tear on the kiln elements etc. 
Plainsman supplies really thorough info on all their claybodies. For Snow the link to it is here, click on each of the subjects and it will expand to give the details. For Snow the absorption figures are below. You can see that it has a huge absorption of 28% when fired anywhere from  cone 06 all the way to cone 2. You can also see that the absorption doesn't drop below 12% even when fired to cone 6. What this means is there is never going to be enough fluxing of the clay to vitrify it enough to be leak proof without a glaze. 
Functional ware made from this clay will need to be stilted when glaze fired. From the Snow page (linked above) it looks like Spectrum 700 glaze fits this body well with Snow being bisque fired to cone 04 and glaze fired to 05.

 

It’s a good question. People end up finding their absorption happy place, some are unsatisfied with anything over 1%, others with 0.5%, I am good if the mugs don’t weep or get wickedly hot in the microwave. I believe that’s below 2%. The ASTM standard for vitrified is 0.5%.
My understanding is similar to yours, about firing range. I could be wrong about this, but my general observation is the lower the maturation temperature of the clay, the narrower the firing range. It’s certain the closer you get to vitreous the less wiggle room you have, at any cone. 
In his book Clay and Glazes for the Potter, Daniel Rhodes says, “Fired stoneware should have an absorption of 3 percent or less.” That’s on page 42 of my edition. I was taught, a few decades ago, that absorption below 2% makes reliable pottery but you should shoot for below 1.5%. Talking to potters over the years gives me the impression that the desired number has crept down since Daniel Rhodes wrote his book. 
Now, back to low fire, is it suitable for everyday use? Not without some careful consideration. There are a lot of variables, so many it seems like a subjective question. It depends on what you’re willing to put up with, or what you’re asking of people who use your pots. I use a lot of earthenware in my kitchen, I wouldn’t expect someone buying my work to deal with that, so I don’t sell anything unless it’s non-absorbent. The issues are strength, absorption, and glaze fit (which really goes back to the first two). The solutions are finding/making a clay body that works and then glazes that fit it. 

Ben, have you seen the work of Jeffery Nichols? He uses unglazed Velvet underglazes on the outside of his pots. Might be worth trying to contact him and asking if he has any research or further info on the durability of unglazed Velvets. Logically they are similar to a highly pigmented stained slip, just with less clay and more flux. 
https://ceramicartsnetwork.org/daily/article/The-Twenty-Year-Teapot-A-Potter-Discusses-the-Lengthy-Process-of-Developing-His-Voice-in-Pottery-and-Shares-His-Teapot-Making-Technique-Too
Pots by Jeffery Nichols

As much of the density or mass in a firing comes from the shelves themselves it's often helpful to put the taller pots on the bottom shelf, shorter pots and more shelves in the middle of the kiln and tall again on the top shelf. (assuming it has with just one thermocouple or is a manual kiln)

As much of the density or mass in a firing comes from the shelves themselves it's often helpful to put the taller pots on the bottom shelf, shorter pots and more shelves in the middle of the kiln and tall again on the top shelf. (assuming it has with just one thermocouple or is a manual kiln)

As much of the density or mass in a firing comes from the shelves themselves it's often helpful to put the taller pots on the bottom shelf, shorter pots and more shelves in the middle of the kiln and tall again on the top shelf. (assuming it has with just one thermocouple or is a manual kiln)

I used to use a Talisman but switched over to using a cordless drill with a brush attachment and a regular plastic sieve that sits in the glaze bucket . WAY easier to clean up!!! Can clean the brush attachment in a small basin or pail of water or under a running tap. Takes seconds and no big sink needed. I have one sieve for clear and light coloured glazes and the other for the dark glazes.
I sold my Talisman.
To give credit where credit is due this idea is from @liambesaw

That’s unfortunate. It will be a question of trial and error to find a commercial clear with low iron contamination to rid the glaze of the yellow tinge. At least from the info supplied in the link above you know which ones won’t be acceptable. Is mixing and testing your own glaze an option?