PeterH

It looks to me like the angular nature could be a crack pattern showing. I've no idea why different regions separated by cracks should show different colours.

Over-firing sounds a likely cause, but it could be that the highly unstable form may be the issue†. (If I understand your description.) Are you glazing, and if so at what temperature? Bone china often needs sitters, and typically has a high bisque firing (so it doesn't stick to the sitters) and a low glaze firing (so it doesn't slump without the sitters). Are you painting yourself into a similar corner? † If a cup-shape slumps you get a distorted cup. If a bent sheet slumps a flat sheet must be a real possibility.

> I read something about pouring out too fast could be creating a glug (not sure if this is slang or a term of art?) where mold might pull off plaster prematurely. Glugging shouldn't be an issue casting bowls. Potters use it with its normal meaning "a hollow gurgling sound or sounds as of liquid being poured from a bottle", and it is caused by the formation of a temporary airlock while filling or emptying the mould. This results in a partial vacuum inside the mould, and is usually only an issue with narrow-necked moulds. A movie is worth a thousand words ... A difficult mould to empty:

The clay will shrink as it dries, which can be problem if the balloon doesn't slowly leak/shrink. I found that a non-intrusive way to let a little air out of a balloon was: - put a strip of sellotape on an accessible part of the balloon - rub to get a good sellotape/rubber seal - prick through the sellotape & balloon with a needle - let some air out - reseal the balloon with another strip of sellotape over the first Try it on a spare balloon first.

Thin pickings. If you have access to Clay Times Magazine Volume 16 • Issue 86 this article might be of interest and/or provide pointers. ... index and some pages (but not the article) in https://issuu.com/claytimes/docs/claytimesbackissuesbernadettecurran ... my interest was based on Description of the show in https://taradawley.wordpress.com/2010/02/03/1053/ ... but couldn't find anything significant there PS Stumbled across this "what's in a name" paper American Shino : A Case Study of Cultural Borrowing in the World of Traditional Ceramics https://konan-u.repo.nii.ac.jp/?action=repository_action_common_download&item_id=4047&item_no=1&attribute_id=22&file_no=1

Some ideas on glazing non-porous bodies in this thread.

I was definitely NOT suggesting that you used bone china, it warps/slumps too much. Just using it as the classical example of high-bisque low-glost approach. If you do read up on it I would concentrate on how they get the glaze to stick to a non-porous body: pre-heating, additives, ...? Will you need the puck to be glazed on all surfaces? If so using stilts is one option, another might be to glaze the "bottom" in an additional lower-fired glazing.

Casting bodies don't need to be very plastic, and can have comparatively low shrinkage. https://digitalfire.com/glossary/slip+casting Slip cast ware can dry-shrink as little as 1.5% (compared to 6%-8% for plastic stoneware bodies). https://www.potterycrafts.co.uk/Products/pottery-powdered-clays/P3101 Shrinkage (w-d) 2 - 4% & Shrinkage (d-f) 6 - 8% So maybe 4% for bisque to fully fired? However you could high-fire to maturity, grind, and then either high or low-fire to glaze -- so zero shrinkage. Bone-china is traditionally fired high-bisque low-glost (it needs to be supported when fired to maturity). Glazing a mature body presents problems, as it isn't porous, but is probably doable (AFAIK industrially various additives are used). PS Solid casting is possible, unless the gradual build-up of clay obstructs the inflow of fresh slip. A hockey puck seems a pretty undemanding shape.

Just or the record, there are several 3D printing pages at digitalfire. 3D Printing a Clay Cookie Cutter-Stamper https://digitalfire.com/video/3d+printing+a+clay+cookie+cutter-stamper 3D-Printing https://digitalfire.com/glossary/3d-printing 3D Design https://digitalfire.com/glossary/3d+design 3D Printer https://digitalfire.com/glossary/3d+printer Project: 2019 Jiggering-Casting Project https://digitalfire.com/project/15

A search for "pizza stone" or something similar will throw up a lot of hits. As you will want to include archived threads in your search, best to use a browser search something like site:community.ceramicartsdaily.org baking stone ... which found the following threads, with a fairly common theme - buy a kiln shelf, if only because you cannot get a suitable clay. Starting with an eerily similar question to your own.

May I suggest that you make a few more birds, a little practice/experimentation goes a long way. Then maybe try for a hollow bird How to make a hollow bird form using thumb pots ... Make a small through hole with a skewer to let any steam generated during firing escape. You can make some bowl-ish items by draping thin class clay slabs over a balloon. e.g. clay over a balloon https://www.pinterest.co.uk/jazzdd76/clay-over-a-balloon/ ... which also mentions a few projects, such as More balloon ideas at Pottery Ballon Technique https://www.pinterest.ca/black3200/pottery-ballon-technique/

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).

... and another method for reducing texture on your 3D printed master, spray paint. See Smooth PLA | No Sanding https://youtu.be/rn4edNztaPU

Speculation ... based on plaster apparently left adhering to your 3D printed mould. Could some of your issues be caused by the "texture" generated by the 3D printing process. Are you are pulling the plaster out of the mould "against the grain" rather than normal to it at the points retaining plaster. (Is the issue texture-scale undercuts rather than PVA/plaster adhesion?) If that's the case, these seem to be some of the ways other people have used to get a smoother/less-textured surface. Sanding 3D Prints: How to Sand PLA & More https://all3dp.com/2/sanding-3d-print-pla/ ... includes How to Print Smooth Parts PLA Smoothing: How to Smooth 3D Prints https://all3dp.com/2/pla-smoothing-a-beginner-s-guide/ UK 3D printing epoxy ads https://tinyurl.com/ebvhn2ed https://tinyurl.com/2jvcuvn3 PS The sacrificial mould technique would probably tend to remove the PLA from the plaster in a direction more normal to the local plaster surface and its texture, which might reduce damage. in some circumstances -- but I don't think it would work well at the edges of the handle. PPS At one point I found an article advising that auto-restart (after power failure) was turned off to get a smoother 3D print, but I cannot find it again. ... this seems to mention the issue. Power Loss Recovery Might Make 3D-Printed Blobs https://hackaday.com/2022/10/10/power-loss-recovery-might-make-3d-printed-blobs/

I also found this forum because general searches found some very interesting postings on it. When I want to use a general browser (mine is google) I default to using site:community.ceramicartsdaily.org PS Just for interest I tried three google searches "red clay" and community.ceramicartsdaily "red clay" community.ceramicartsdaily "red clay" site:community.ceramicartsdaily.org Which returned 12,700, 15,000 & 594 results respectively. (The order, and possibly the number, of results may/will-be influenced by my previous search history.) Repeating the searches a few minutes later I got 13,400, 15,400 & 757 results. Just reporting the number of results, not judging their quality.

Tony Hansen strikes again. in https://digitalfire.com/picture/2463 The incredible utility of 3D printing master handle molds As a parting-agent I use Murphy's Oil Soap on the 3D-printed PLA mold, this makes it fairly easy to extract the freshly-cast plaster molds (the sidewalls have a draft of about 5 degrees).

Why not ask her https://www.instructables.com/member/Charlotte_J/instructables/

I was reminded of a different approach to the same 3D printing idea. It used sacrificial 3D prints, and produced moulds with minimal excess plaster. 3D Printing a Mold for a Slipcasting Mold https://www.instructables.com/3D-Printing-a-Mold-for-a-Mold/ Obviously horses for courses, but maybe something for your notebook.

For non-brits, the UK 13A ring main is described in http://wiki.diyfaq.org.uk/index.php/Ring_circuit The ring circuit and BS 1363 plug and socket system were developed in Britiain during 1942-1947.(ref 1) They are commonly used in the United Kingdom, and to a lesser extent in the Republic of Ireland. The ring circuit came about because Britain had to embark on a massive rebuilding programme following World War II.(ref 2). There was an acute shortage of copper, and it was necessary to come up with a scheme that used less copper than would normally be the case. The scheme was specified to use socket outlets with 13 Amp fused plugs. ... The ring circuit was devised during a time of copper shortage to allow two 3kW heaters to be used in any two locations and to allow some power to small appliances, and to keep total copper use low.

To measure the resistance you could measure it at the switch (turned off, maybe power off as well), or remove the connections from the switch and measure via the leads. You can measure current with a clamp ammeter, although you might need to jury-rig a connection to do so. Just one of the power leads (live or neutral) has to be inside the clamp. eg https://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=clamp+ammeter&_sacat=0&_sop=15

I've been thinking along similar lines, but wondering if they are 220v elements run at 240v. As power is proportional to V^2, this would give (240/220)^2*2000 ~2380w at 240v. ... probably not good for element life, so your series comment seems even more appropriate. PS 220v would give 2000w with a resistance of 220^2/2000 = 24.6 ohms. So if the current resistance is 26 ohms that's about 100*(26/24.6-1) ~ 5.6% gain over time.

Can you post a picture of the kiln plate? PS I haven't yet found anything on CTL-17s on the net, but many of the CTLs seem to exist in 220v & 240v versions. The CTL28 is listed as a 3KW kiln for 220v & 240v operation in https://www.cromartiehobbycraft.co.uk/files/Kiln Downloads/CTL Range Leaflet (1st).pdf But both 3.0kw and 3.3kw versions of the elements are offered here https://tinyurl.com/58knhuwy ... other models seem to have an optional N suffix, for which a higher wattage element is sold. Might be worth asking Cromartie what they think the resistance of your element(s) should be.

Thread on ITC coatings.

A couple of minor points if you are still trying to increase the crazing. 1) Always ink-up (part of) your test-tiles. It can sometimes be hard to see the true extent of the crazing. It also gives you a better idea of the number of cracks which occur after the initial inking. an example from Digitalfire 2) I understand that glaze programs are not too accurate at estimating the absolute COE of a glaze, but they are quite good at estimating the change to the COE that small change to the recipe/chemistry will make. So maybe you are reaching the point where they might be useful. See Using Calculation to Fit a Glaze in https://digitalfire.com/article/understanding+thermal+expansion+in+ceramic+glazes

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.