PeterH

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).

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.

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

Good spot. Several nice examples in https://wander-lush.org/clay-qvevri-wine-shrosha/ including ... and support in the kiln with bricks & small stones

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.

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.

Are you going to fit a current sensor?

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

Just for the record (as there are obviously bigger issues involved). Assuming Min is right and wet clay contains 20-23% water -- and if dry clay contains none -- I think you should get 25-30% more clay per lb. 20/(100-20) = 0.25 = 25% 23/(100-23) = 0.2987 ~30%

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?

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

Has anybody any idea why there would be barium carbonate in a black glaze? ... on second thought maybe it's to give a velum matt finish. If the barium isn't significantly effecting the colour, and the glaze is already matt, would this minimise the chances of a vinegar test showing anything (even if barium was being leached)?

I vaguely remember Ian Gregory (of fibre kiln fame) making a similar comment during a demonstration -- about being able to fire a kiln-full of freshly thrown pots without trouble. He then immediately said that with somewhat dryer pots this didn't work. The impression I got that there was a brief sweet-spot where this was possible (and then only for a kiln-full of such pots), not that the state of dampness wasn't important. I've no coherent theory to explain/understand this claim. Although its possible that some sort of wicking process draws the water to the surface as the pot dries, and the large number of wet pots in the kiln limits the temperature ramp while there is still surface water to evaporate. Surface drying before firing could prevent such wicking of water to the surface during firing.

This earlier post by @Jeff Longtin may be of interest

Perhaps of mild interest, despite cryptic translation. https://patents.google.com/patent/CN1055278C/en Method for making colour glaze natural leaf figure ceramic product Abstract The present invention discloses a method for making color glaze natural leaf pattern ceramics. Natural leaves or plant leaves are stuck to a blank coated with base glaze after particularly treated, and a layer of surface glaze is coated on the blank. Then, the blank is put in a kiln to be burned to obtain a ceramic finished product. The present invention uses ceramics as a carrier, and natural leaf patterns are burned on the ceramics. The leaf patterns are clear, natural and vivid and have beauty sense and very high appreciation and collection value. The present invention has no particular requirements for conditions of the base glaze, the blank, combusting atmospheres, etc. and has the advantages of simple preparation process and easy operation.

Hang on ... it's still out there. Usable link below A google for TRANSFORMATION_OF_SIX_LEAVES_GLAZE_TO_CONTEMPORARY_CERAMIC_BASES_ON_THE_TAOISM_CHARACTERISTICS filetype:pdf gets me to an Resource not found error page at http://www.sure.su.ac.th/xmlui/bitstream/handle/123456789/20993/DR_FENG_Shanxin.pdf?sequence=1&isAllowed=y Clicking on Go to SURE home get me to the sites home page at http://www.sure.su.ac.th/xmlui/ From there a search for TRANSFORMATION OF SIX LEAVES GLAZE gets me to the pdf at http://www.sure.su.ac.th/xmlui/bitstream/handle/123456789/24111/DR_FENG_Shanxin.pdf?sequence=-1&isAllowed=y I give the search details as it's possible that you may find other items on the site of interest. PS ... and an alternative URL, possibly to the same instance of the file : http://ithesis-ir.su.ac.th/dspace/bitstream/123456789/2977/1/60155902.pdf

Setter is a name for types of kiln furniture which offer some protection against slumping/distortion. https://www.earthwaterfire.com/products/setters/ Ceramic Setters are special items of kiln furniture which, in the ceramic tableware industry, are shaped (generally on their upper surface) to conform with the undersurface of plates and dishes and which serve to support ware and maintain its shape in the kiln during Setters are especially important when firing bone china. https://ceramicartsnetwork.org/pottery-making-illustrated/pottery-making-illustrated-article/Tempting-Transparency# In cases where the bisque firing is much higher than the glaze firing, as is normally when working with the case with bone china (between 2246–2300°F (1230–1260°C)), it’s essential that the clay ware receives the maximum support during the firing process, particularly as most of the movement occurs when the kiln reaches its highest temperature. Due to the high distortion factor encountered with bone china, if the shape is to be controlled, any open form requires a setter of some kind. If the form is circular at the top, it can be placed upside-down on a refractory clay ring, or setter, with an alumina wash to prevent sticking in the firing. If the form is irregular at the top edge an individual setter needs to be made. In simple terms, this is an item that resembles a lid and is cast separately (the preferred making method for bone china). Its function is to contain the top edge, or rim, of a form during firing (figure 10) and is discarded afterward. If the piece has been successfully fired with no distortion, the ware can be glazed and fired at a lower temperature of 1832–1976°F (1000–1080°C), if necessary.

http://www.vincepitelka.com/handoutsinformation /https://www.vincepitelka.com/wp-content/uploads/2019/02/Low-Pressure-Gas-Orifice-Chart.pdf http://www.wardburner.com/

Can somebody point me to an Orton chart which shows the temps for small and self-supporting cones when fired at the same rate? PS The first chart I found gives the (different) cone temps for small cones at a significantly higher firing rate for the small cones. ... this page, while referencing the same Orton charts, implies that small and self-supporting cones operate at the same temps (when heated at the same rate). https://nmclay.com/informational-pages/orton-cone-chart-in-centegrade ... but gives no Orton reference for this

Do you still have access to the clay and wheel at college? If so might be worth trying home clay wedged at home on the college wheel, and vice versa. It might at least remove some variables. ... and carefully consider any differences in body/arms/wheel/chair relationships in the two situations.

Pedantically, as P=V^2/R wouldn't a change from 12v to 16.5v to increase the power by a factor of (16.5/12)^2 = 1.89? I've no idea how much this would change the operational life of the relay though.

Do you mean like this? 3D Printing a Mold for a Slipcasting Mold https://www.instructables.com/3D-Printing-a-Mold-for-a-Mold/ Looks like a viable way of making individual parts of a multi-part mould.

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

John Britt's summary of kiln wash recipes, with some thoughtful explanations. The Many Layers of Kiln Wash: How to Find the Best Kiln Wash for Your Firing Temperature and Methods https://tinyurl.com/3695jpf2 ... and a deflocculated variant of one of them Self-Leveling Kiln Wash https://jeffcampana.com/self-leveling-kiln-wash/ and https://glazy.org/recipes/42065 PS From the comments section of the self-leveling kiln wash paper John Britt says: October 11, 2010 at 11:21 am Nice Jeff, I believe that is called Lee’s Incredible Kiln Wash” $25.00 a gallon on Etsy, ... although contrast with @Bill Kielb's earlier comment Folks have “speculated” that Lees is zircon based. I am not sure anyone knows it’s actual composition