PeterH

try to think this sentence as :  "then glaze with the transparent glaze"
The brush action is different to painting.  Glazing needs a loaded brush and allow the glaze to flow off the end of the brush in one sweep, then turn the brush over, and apply the next sweep to the next part of the pot.  Never scrub the glaze onto your pots like you might do with paint.  Painting and glazing are different actions, and need the different words stuck in your mind so you remember that.
So, to recap all the above comments:
bisque firing is to change clay (that can be re-wetted and turned back into workable stuff) into clay that is hard, but still porous.  Usually to cone 06-04
glaze-firing should turn the bisqued pot into a stronger, (vitirified ?) non-porous pot that will hold water.  Earthenware temperatures need fully glazing, stoneware temps can/should have bare bottoms and don't need to be fully glazed to be non-porous.  Can be cone 04 through to 6, 8, 12 or higher.
 
Any more questions - keep asking.
 

This thread may be relevant:
Have you fired any test tiles?  If the above is relevant I would have expected them to come out something like the outside of your mug.

https://youtu.be/2xOGWsFJ4DA
I'm interested if you remember any more details . The closest thing I've found yet is this:

Video at  https://youtu.be/2xOGWsFJ4DA
I wonder if you can do the same thing with coil-building (which may be necessary/helpful for larger pots).
 

... or maybe you were remembering this. Which I suspect wouldn't generalise scale to a 30 gallon qvevra.

https://tinyurl.com/36ap7kh8

Good spot.
Several nice examples in https://wander-lush.org/clay-qvevri-wine-shrosha/ including

... and support in the kiln with bricks & small stones

https://youtu.be/2xOGWsFJ4DA
I'm interested if you remember any more details . The closest thing I've found yet is this:

Video at  https://youtu.be/2xOGWsFJ4DA
I wonder if you can do the same thing with coil-building (which may be necessary/helpful for larger pots).
 

How do you support the pieces when firing; flat on the shelf, on a waster, on sand, ...?

Any help? https://davidneat.wordpress.com/tag/preparing-styrofoam-for-silicone-rubber-covering/

Not for sure, but they look a little like broken terra cotta roof tiles. Could be that they’re using some kind of waster they just had around. I imagine that you could cut some from wood if that’s the material you have to hand.
 

Wow, it only takes 10 mins.
Throwing/ Making a Onggi Pottery(Part 1 of Part 2)Korean Potter

Stumbled across this while researching my last post. In case anybody is interested ...

Throwing Punic Amphorae: An Archaeological and Experimental Approach to the use of the Potter's Wheel in southern Iberia during the Iron Age
https://exarc.net/issue-2021-2/ea/throwing-punic-amphorae-archaeological-and-experimental-approach
A slightly odd format as the text is in a pdf file, and the diagrams have to be downloaded separately.

I've no personal experience on making large pots, but I'd like to give a few estimates of wall thickness. I'll use metric units (30 US gallons is about 114 litres).  
1) The long history on amphora for both storage and transport.
Digital modeling of function and performance of transport amphorae
https://ceramics.onlinelibrary.wiley.com/doi/full/10.1002/ces2.10056
... which describes relatively small vessels from 26.8 to 44.5 litres, states
The indicated weights of the empty vessels correspond to a uniform wall thickness of 10 mm and an assumed density of the ceramics of 1.7 g/cm3.
I find the thinness of the walls a little surprising considering the stresses and strains that would occur when they were used for transporting goods. Where they would encounter a fair degree of man-handling and other stressful environments.

2) Qvevri shapes and dimensions.
Wine and Food Travel: Qvevri Wine Making Tradition of Georgia
https://www.indianwineacademy.com/item_6_622.aspx
... which links to a larger version of this image showing the relationships between the various dimensions of a family of Qvevri.

This states that the wall thickness is between 2 and 5 cm. The upper figure being quite low considering the size of some vessels.
Although Quevri leave largely static lives (especially the well-supported buried ones)  the wall thickness has to support man-handling during construction and while moving to its final location. The neck area in particular needs to be suitable for the use of ropes.
It also gives an approximation to the volume of a Qvevra, which is the same as that of an ellipsoid of the same width and height.
 
 
3) Modern Qvevri for sale
From http://www.domainegeorgia.com/order.html

The 120 litre one is closest size to 30 US gallons, and I'll try to estimate its wall-thickness from the information available, modelling it as an ellipsoid (in units of ml and grams).
v  = volume of an ellipsoid with same width and height = 4/3*pi*(50/2)^2*55
c = internal volume with wall of thickness t = 4/3*pi*(50/2-t)^2*(55-t)
w = volume of clay walls = 60*1000/(density of ceramic) = 60*1000/1.7 ml
Now  w = v - c giving
60*1000/1.7  = 4/3*pi*(50/2)^2*55 - 4/3*pi*(50/2-t)^2*(55-t)
v = 4/3*pi*(50/2)^2*55
c = 4/3*pi*(50/2-t)^2*(55-t)
Sticking these into a symbolic maths package such as  https://www.dcode.fr/equation-solver gives

So the estimated capacity is fairly close to the advertised 120 litres, and the estimated wall thickness 2.72cm (1.07 inches) for a real-world  Qvevra of ~120 litres. Again surprisingly thin considering the manhandling it will get, although  (unlike amphora) it is only moved while empty (and lighter).
4) Comments on building and shape.
Fairly obvious comment, they do seem to "work to coil" heavily, presumably to minimise weak-spots due to non-uniformity. As can be seen in  https://www.redfedoradiary.com/qvevri-georgian-wine/


The conical bottom to the interior seems to be functional (grape seeds fall into it and are covered in lees, keeping bitter compounds from entering the wine). Prompted by Pres's query I realised all the pictures of making Qvevri I can remember have the potter walking round a fixed pot. Considering the size of large Qvevra putting "pointy" ones on any sort of turntable might be difficult, balancing them while turning it even more so. They usually seemed to be propped up on the ground like so:

Does anybody know how/if smallish pointy Qvevri can-be/are built on a wheel?
 


 
 
 

From https://tinyurl.com/jtcjby88
We also purchased this $34 amperage detector from Bartlett which is a tiny circuit board you connect to the kiln controller and has two white leads connecting to a ferrite ring.
You thread one 220 volt power lines from each relay to the heating elements through the ferrite ring, which measures the power being consumed.  This allows the controller to compare your current power draw to the original power draw when you installed the elements or in our case when we installed the controller.
The controller tests the elements for about 60 seconds prior to each firing.  A decline in amperage used is charted to determine your element aging and any sudden decline indicates the failure of an element.

I think it also does other helpful things, like reporting the power consumed (and its cost). Don't know if it can detect things like stuck relays in real time.

Important practical point well worth emphasising, but I did say per lb.

This also assumes that the dry clay is the same cost per pound as the moist clay. When I worked for A.R.T., we charged more for dry mix because mixing and bagging dry clay was a much slower process for us than making moist clay.

I've no personal experience on making large pots, but I'd like to give a few estimates of wall thickness. I'll use metric units (30 US gallons is about 114 litres).  
1) The long history on amphora for both storage and transport.
Digital modeling of function and performance of transport amphorae
https://ceramics.onlinelibrary.wiley.com/doi/full/10.1002/ces2.10056
... which describes relatively small vessels from 26.8 to 44.5 litres, states
The indicated weights of the empty vessels correspond to a uniform wall thickness of 10 mm and an assumed density of the ceramics of 1.7 g/cm3.
I find the thinness of the walls a little surprising considering the stresses and strains that would occur when they were used for transporting goods. Where they would encounter a fair degree of man-handling and other stressful environments.

2) Qvevri shapes and dimensions.
Wine and Food Travel: Qvevri Wine Making Tradition of Georgia
https://www.indianwineacademy.com/item_6_622.aspx
... which links to a larger version of this image showing the relationships between the various dimensions of a family of Qvevri.

This states that the wall thickness is between 2 and 5 cm. The upper figure being quite low considering the size of some vessels.
Although Quevri leave largely static lives (especially the well-supported buried ones)  the wall thickness has to support man-handling during construction and while moving to its final location. The neck area in particular needs to be suitable for the use of ropes.
It also gives an approximation to the volume of a Qvevra, which is the same as that of an ellipsoid of the same width and height.
 
 
3) Modern Qvevri for sale
From http://www.domainegeorgia.com/order.html

The 120 litre one is closest size to 30 US gallons, and I'll try to estimate its wall-thickness from the information available, modelling it as an ellipsoid (in units of ml and grams).
v  = volume of an ellipsoid with same width and height = 4/3*pi*(50/2)^2*55
c = internal volume with wall of thickness t = 4/3*pi*(50/2-t)^2*(55-t)
w = volume of clay walls = 60*1000/(density of ceramic) = 60*1000/1.7 ml
Now  w = v - c giving
60*1000/1.7  = 4/3*pi*(50/2)^2*55 - 4/3*pi*(50/2-t)^2*(55-t)
v = 4/3*pi*(50/2)^2*55
c = 4/3*pi*(50/2-t)^2*(55-t)
Sticking these into a symbolic maths package such as  https://www.dcode.fr/equation-solver gives

So the estimated capacity is fairly close to the advertised 120 litres, and the estimated wall thickness 2.72cm (1.07 inches) for a real-world  Qvevra of ~120 litres. Again surprisingly thin considering the manhandling it will get, although  (unlike amphora) it is only moved while empty (and lighter).
4) Comments on building and shape.
Fairly obvious comment, they do seem to "work to coil" heavily, presumably to minimise weak-spots due to non-uniformity. As can be seen in  https://www.redfedoradiary.com/qvevri-georgian-wine/


The conical bottom to the interior seems to be functional (grape seeds fall into it and are covered in lees, keeping bitter compounds from entering the wine). Prompted by Pres's query I realised all the pictures of making Qvevri I can remember have the potter walking round a fixed pot. Considering the size of large Qvevra putting "pointy" ones on any sort of turntable might be difficult, balancing them while turning it even more so. They usually seemed to be propped up on the ground like so:

Does anybody know how/if smallish pointy Qvevri can-be/are built on a wheel?
 


 
 
 

We did this in college. I can confirm this is very hard on your body, and I was 23 the last time I did it. Soldner doesn’t seem to have believed in such frivolities as excess clothing or equipment ergonomics. Reaching into that barrel repeatedly to lift out heavy stuff in the name of lifestyle isn’t my jam: I don’t like mid to lower back pain. I agree with Kelly that it’s something you should do once, and decide from there if you want to keep doing it.
If it’s just down to money, you need to math out the costs vs benefits for your own situation.  While you’d be getting 20-23% more clay if you get dry mix, you’d be giving up the time in the form of days you’re taking to mix it. You’re also paying in terms of wear and tear on your body, especially your back. Does the unit price savings justify your added prep time and potential for injury? I’m not assuming the answer is no here. It might be a perfectly good, cost effective answer for you.
 How critical is that exact clay body to your work? Can it be substituted with something more easily sourced, or is it  just that you’re far away from everything?
If prepared clay drying out is a concern, Mark has mentioned in the past that he gets his supplier to mix half of his order a bit softer to counteract this. Does your supplier offer this as an option?

A pboto would be good.
What cone have you fired glaze to?
Just if glaze is immature it may clear a bit if fired higher, on a waster slab. Is this result way different to other work or test tiles  using this glaze ?

I've no personal experience on making large pots, but I'd like to give a few estimates of wall thickness. I'll use metric units (30 US gallons is about 114 litres).  
1) The long history on amphora for both storage and transport.
Digital modeling of function and performance of transport amphorae
https://ceramics.onlinelibrary.wiley.com/doi/full/10.1002/ces2.10056
... which describes relatively small vessels from 26.8 to 44.5 litres, states
The indicated weights of the empty vessels correspond to a uniform wall thickness of 10 mm and an assumed density of the ceramics of 1.7 g/cm3.
I find the thinness of the walls a little surprising considering the stresses and strains that would occur when they were used for transporting goods. Where they would encounter a fair degree of man-handling and other stressful environments.

2) Qvevri shapes and dimensions.
Wine and Food Travel: Qvevri Wine Making Tradition of Georgia
https://www.indianwineacademy.com/item_6_622.aspx
... which links to a larger version of this image showing the relationships between the various dimensions of a family of Qvevri.

This states that the wall thickness is between 2 and 5 cm. The upper figure being quite low considering the size of some vessels.
Although Quevri leave largely static lives (especially the well-supported buried ones)  the wall thickness has to support man-handling during construction and while moving to its final location. The neck area in particular needs to be suitable for the use of ropes.
It also gives an approximation to the volume of a Qvevra, which is the same as that of an ellipsoid of the same width and height.
 
 
3) Modern Qvevri for sale
From http://www.domainegeorgia.com/order.html

The 120 litre one is closest size to 30 US gallons, and I'll try to estimate its wall-thickness from the information available, modelling it as an ellipsoid (in units of ml and grams).
v  = volume of an ellipsoid with same width and height = 4/3*pi*(50/2)^2*55
c = internal volume with wall of thickness t = 4/3*pi*(50/2-t)^2*(55-t)
w = volume of clay walls = 60*1000/(density of ceramic) = 60*1000/1.7 ml
Now  w = v - c giving
60*1000/1.7  = 4/3*pi*(50/2)^2*55 - 4/3*pi*(50/2-t)^2*(55-t)
v = 4/3*pi*(50/2)^2*55
c = 4/3*pi*(50/2-t)^2*(55-t)
Sticking these into a symbolic maths package such as  https://www.dcode.fr/equation-solver gives

So the estimated capacity is fairly close to the advertised 120 litres, and the estimated wall thickness 2.72cm (1.07 inches) for a real-world  Qvevra of ~120 litres. Again surprisingly thin considering the manhandling it will get, although  (unlike amphora) it is only moved while empty (and lighter).
4) Comments on building and shape.
Fairly obvious comment, they do seem to "work to coil" heavily, presumably to minimise weak-spots due to non-uniformity. As can be seen in  https://www.redfedoradiary.com/qvevri-georgian-wine/


The conical bottom to the interior seems to be functional (grape seeds fall into it and are covered in lees, keeping bitter compounds from entering the wine). Prompted by Pres's query I realised all the pictures of making Qvevri I can remember have the potter walking round a fixed pot. Considering the size of large Qvevra putting "pointy" ones on any sort of turntable might be difficult, balancing them while turning it even more so. They usually seemed to be propped up on the ground like so:

Does anybody know how/if smallish pointy Qvevri can-be/are built on a wheel?
 


 
 
 

I’ll give you my take. The vinegar test is very helpful and many glazes ought to pass it. Does it indicate durability, not necessarily so. It’s a nice test that can be done at home and any commercial ware ought to easily pass it IMO. Will it predict some of the complaint issues mentioned earlier which could go to glaze durability, glaze fit? Most likely not. Will it always predict leaching? Really not necessarily so, that is more of a lab thing. It’s definitely a good test to pass though. When a glaze does not pass it, for sure it is usually judged not a good glaze for food consumption.

Nancy, are you looking to make yours with the pointed/rounded base or with a flat base? I believe that part of the process is determined by the base. Thickness of the larger pots seems to be 2-4" in coils, and then the scraping will bring the walls a little thinner. flat bottoms have more stress on the bottom for weight of the walls whereas the rounded or pointed bottoms are supported with the side walls with different stress points. Interesting project. . . wish we could help more. I would think your best efforts would be to work smaller and ramp up when  you get more assured/confident of your process.
 
best,
Pres

I wold think that even at 30 gallons they would not need to be especially thick. Clay is strong stuff. Just picturing a 30 gallon trash can, 1/2" walls should be able to hold it. It would be difficult to build that thin, though, so I would just do what you can and not worry about it.

Hi, Nancy! Glad you’re back to your project. Technically, I think it’s not the thickness of the walls but the soundness of them that keeps vessels whole under the pressure of the contents. You want to have a consistent thickness and no cracks for good drying and firing. A five foot tall jar might need up to 2” thickness, a two foot jar maybe less than 1”, but that is for strength during construction and firing, not strength against internal pressure, which comes from no cracks or fissures. (Burial was both the preventative and the cure for ancient cracked vessels.)
There are YouTube videos of coiling large jars. Generally, the coils are about 1”-1 1/2” in diameter - human hand scale. 
 

@PeterHThink it aids with that metallic look folk seem to like eating from a.t.m.
If prepared to sell barium based  dinnerware, could also contain chrome, eh?

Haven't been able to find anything more about this:
http://www.potters.org/subject98825.htm
Frank Colson on sun 4 feb 07
Some many years ago, I published an article called: Total Wet Firing. I
would take a freshly thrown pot off the wheel head and fire it immediately
in a preheated raku type kiln Did a workshop for a group of local art
teachers, so we were able to "experiment" this type of firning with more
than 100 pots so we were able to get all te wrinkels worked out. You might
call
the approach a one-upmanship raku technique. Allthough I still have one pot
on my shelves, it was great fun but not very peranent. The entire firning
proces took about 5 minuets!

If anywone would like to see how to do "Total Wet Firing", I'll put it on my
website as a free download.

Frank Colson
www.R2D2u.com