PeterH

Fine if you didn't have the slot and the form almost supported itself. But IMHO the area near the slot is going to droop unless it is supported over ~100% of its surface.

There is a little bit on one-use setters for bone china in Tempting Transparency https://ceramicartsnetwork.org/pottery-making-illustrated/pottery-making-illustrated-article/Tempting-Transparency# Ideas on the body to use for multi-use setters Bone China AntiWarp Setter test molds https://digitalfire.com/picture/3156 ... Tony Hansen uses a "kiln shelf" body for his setter L3693H1

But why in this glaze - and in Snowflake Crackle - do the cracks mainly appear to propagate parallel to the glaze surface rather than normal to it? There only seems to be two options: somehow the stress in normal to the glaze surface, or something is causing the propagating crack to change direction from normal to parallel to the glaze surface. ‡ PS The usually physical model for "fast" crack propagation just doesn't seem to apply here.† Hierarchical crack pattern as formed by successive domain divisions. I. Temporal and geometrical hierarchy https://tinyurl.com/3yu6wx6y † There is another model for "slow" cracks (where several may be propagating at the same time), for example mud drying. ... and the less relevant Hierarchical crack pattern as formed by successive domain divisions. II. From disordered to deterministic behavior. https://tinyurl.com/26w8ap4p ‡ Maybe there is some link with conchoidal fractures ( which explains how flint-knapping works)? † There is another model for "slow" cracks (where several cracks may be propagating at the same time), for example mud drying. PS Irrelevant to the present discussion, but an example of complex 3D cracks. Evolving fracture patterns: columnar joints, mud cracks and polygonal terrain https://royalsocietypublishing.org/doi/epdf/10.1098/rsta.2012.0353

I was looking at some of the colours in the original pictures and somewhat reluctantly came to the conclusion that they might indicate that the colour of the glaze varied with depth. Which of course some people have been saying for a long time about some copper reds. This made we wonder what would happen if you applied two differently coloured layers of snowflake crackle glaze. Would you get interestingly coloured patterns?

I think you've got it. Horizontal cracks within the glaze (acting as reflectors) would affect the colour (by reducing the distance light travels in the glaze) even if the colour is uniformly distributed in the glaze. The small amounts of colourants in copper-reds might also be significant. Snowflake Crackle https://ceramicartsnetwork.org/ceramic-recipes/recipe/Snowflake-Crackle Color The first thing I noticed when I did color tests with the usual colorants and opacifiers (copper carbonate, red iron oxide, chrome oxide, stains, Zircopax Plus, etc.) was that, as the color improved, the crazing ceased. This was because all oxides have expansion/contraction rates and adding them changed the CTE of the glaze enough to stop the crackle effect. I ran more tests with very low levels of colorants (under 1%), which kept the crazing yet still produced a nice color. PS Do you have any similarly fired pots which didn't show this effect? An ice-water stress test might be interesting. PPS I wanted to suggest that the relative freedom from cracks near the edge of the bowl was a significant clue, but couldn't word it right. So here is a picture of the effected -- with a smaller crackle size and hence smaller outside ring. I've been testing a Snowflake crackle glaze. Here it is over coloured slip https://www.reddit.com/r/Pottery/comments/8jjxxi/ive_been_testing_a_snowflake_crackle_glaze_here/

Interesting idea, do you have any specific approaches in mind? Lithium extraction from hard rock lithium ores (spodumene, lepidolite, zinnwaldite, petalite): Technology, resources, environment and cost http://en.cgsjournals.com/article/doi/10.31035/cg2022088 Lithium extraction from mechanically activated of petalite-Na2SO4 mixtures after isothermal heating https://www.sciencedirect.com/science/article/abs/pii/S089268752030114X ... full paper behind a firewall, but the relative solubilities of Na2SO4 & Li2SO4 suggests that Li2CO3 would precipitate out first.

Puzzled brainstorming. Wild idea for the colours, but not the cracks, fuming copper pooling in the bowl? I don't claim to fully understand copper reds. But fumed copper is presumably more likely to be present near the surface (and blue/green?), while there is a persistent argument that (some? all?) of the red is down below the surface. The Dual Mechanisms of Tin Oxide in Copper Red Glazes https://glazy.org/posts/168150 On second thoughts ... We seem to have a "paint-by-numbers" of regions: each of more-or-less uniform colour; with the sections delineated by cracks that almost certainly weren't there when the colours were formed. Large local differences in composition might explain the positioning of the cracks, but it's hard to see how that could happen. Could it be caused by differences in surface texture/crystallisation? That might add surface reflections (colour), and also influence crack initiation/propagation (position). Any chance of a specular-reflection free image of the same location? PS >And, to note, the pieces rang like a bell out of the kiln. Can you remember if they had the angular colour pattern before they cracked? Yes - the colour differences are controlling the position of the cracks? Surface texture influencing both? No - the cracks are causing the colour differences? Is it conceivable that the release of stress caused by the crack changes the surface texture?

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.