PeterH

A few thoughts on your crystals - As you cannot dissolve them in hot water this might indicate that they aren't boron-based. - If you have dilute hydrochloric acid it will dissolve most calcium salts, including the silicate ... see A in http://www.pharmacopeia.cn/v29240/usp29nf24s0_m12120.html If you find a way of reproducibly creating the crystals it might be interesting to try: - Using a different deflocculant (Darvan?), which will probably change the pH of the slip which might change things. - Seeing if a small addition of sugar to the fresh slip influences the growth of the crystals [*] [*] Adding sugar would probably be very bad for the moulds, but just might form an interesting experiment. I mention it because sugar has a significant effect on the settling time of cement, apparently by its surface action on things like Wollastonite.

Just to mention the discussion of unwanted crystal growth in http://ceramicstoday.glazy.org/articles/flambe_magic.html ... it also makes me wonder if there could be a "pumping" action if the liquid is repeatedly warmed and cooled.

... and even if it's only "yellow" dextrin it would probably be a better starting point than cornstarch for your own processing.

Dextrin is readily available from small-scale pyrotechnic ingredient suppliers (if you can find them). My limited experience of these (looking for pottery ingredients) suggests that they are fairly cheap and very technically savvy. But I've no real idea how to assess the "quality" of the dextrin they supply (other than it's suitability as a firework ingredient). US example https://www.fireworkscookbook.com/product/dextrin/ I suppose that you could try asking them for advice.

>If anyone is aware of a small quantity source for the darker, more deeply pyrolyzed starch sizing/adhesive called "British gum" please let me know. May be of relevance. Pyrotechnics data for your hobby: Dextrin https://pyrodata.com/chemicals/Dextrin Sources: Dextrin is easily prepared from starch. Potato and cornstarch will both work fine. The starch is spread out on a sheet in a layer about 1 cm thick and placed in the oven. The oven is then heated to 220°C(400°F) for several hours. The dextrin will turn slightly yellowish brown. One way to check if all the starch has been converted is to dissolve a small sample in boiling hot water and add a drop of KI3 solution (Lugol's iodine solution). A blue colour indicates presence of starch, which means the conversion hasn't completed yet. KI3 solution is conveniently prepared by dissolving a crystal of elemental iodine in a potassium iodide solution. The complete removal of starch could be important in your application, so I would try the starch-iodine test. PS Dextrin and Making Dextrin http://www.wichitabuggywhip.com/fireworks/dextrin.html

If you are trying different brushes & handling techniques there is a Chinese calligraphy practice paper/cloth that you can draw on with a water filled brush. When wet it gives a dark image which slowly fades as it dries. Often called magic-paper/cloth. Sometimes it has guide-lines for calligraphy, but plain sheets are also available. PS another sort of specialised brush

More types of ruling pin nibs than I'd thought (my only experience is a little technical drawing 60 odd years ago). All About Ruling Pens https://sarahtypes.com/all-about-ruling-pens/ https://www.johnnealbooks.com/prod_detail_list/ruling-pen-basics

No experience, but might that have been done with a ruling pen? Although these are often used to make very uniform "ruled" lines I believe that shifting the angle of use can produce varying line widths. This example seems to have a similar blotch-iness in the thicker lines in your example. Are You Using Your Ruling Pen to its Full Potential? https://garnerwildlifeart.wordpress.com/2021/05/28/what-is-a-ruling-pen/

Just eye candy: glazes where slow cooling can have a dramatic effect. From Super Cool! Slow Cooling in an Electric Kiln https://ceramicartsnetwork.org/daily/article/Super-Cool-Slow-Cooling-in-an-Electric-Kiln ...and

Might have been this one, where the choice of terminology seemed to be a hindrance rather than a help. I'll freely admit that I'm not sure what temper means, and I'm pretty sure that it means different things to different people. One meaning is: Temper is non-plastic material that is added to clay to keep it from cracking when it dries. It is most often sand, ground stone or ground fired ceramics but historically a wide range of materials have been used for temper. e.g. see Tempering Pottery Clay https://ancientpottery.how/tempering-pottery-clay/ Temper (pottery) https://en.wikipedia.org/wiki/Temper_(pottery) Another meaning relates to the non-pottery specific definition of tempered as limited or controlled, or made less extreme https://dictionary.cambridge.org/dictionary/english/tempered ... and I expect that there are others. OTOH you seem to want an additive to achieve a really smooth clay. So I don't think its currently cracking, and you are trying to make its smoothness more extreme. So I suppose I'm asking if something like "less gritty" or "more plastic" would capture your intentions better (and leave less room for misunderstandings). PS What mesh-size is your final sieve? Particle Size in How to Find and Test Your Own Native Clays https://digitalfire.com/article/how+to+find+and+test+your+own+native+clays But for fine functional ware, you will need a way to screen out +100 mesh sizes (see links below).

What position is your 3-position rocker switch in?

There's a brief thread on a Ceradel Socor kiln at Yours should have a plate on it giving some important details. It might look something like this

Perhaps it's worth glancing at this, which looks at the effects of different SiC mesh sizes in lava glazes. Testing Silicon Carbide Grits in Cone 6 Lava / Crater Glazes https://www.thestudiomanager.com/posts/testing-silicon-carbide-grits-in-cone-6-lava-glaze

Back up to his posting on this thread, and click on the big P. Then click on the Message icon, and you are messaging him -- by email so he doesn't even have to access the forum to see it. ... keep an eye on the icon at the top of the forum page to catch any personal messages addressed to you (it changes colour).

Are you sure that this isn't an indirect reference to heat-work? Perhaps in the context of unachievable ramp speeds.

These seem to be "wild" North Carolina clays (singly or as mixtures?). I've no idea if/where they might be bought, or how they might be approximated from commercial clays. Jeff makes a good point: if you are approximating the look of these clays then stains could simplify the process, especially if you wanted a palette of colours. From Wild Clay: The Story of NC Clay https://www.woodfirenc.com/wild-clay Sorry about the text size. Also see https://bandanapottery.com/materials Our main clay body… Our main clay body is mostly (75%) comprised of a mixture of two clays from our area: A coarse, red clay that is near our home in the higher mountains, and a more plastic grey clay that settled near a creek bed further down the mountain. We mix these wild clays into a slip and pour them through a screen into a large feed tank. The screening process is one of the first aesthetic and expressive decisions we make- the size of the screen determines the final landscape of particles in the clay beneath our slips and glazes. While dark in color, both these clays are so refractory in their pure state that we still need to add feldspar to the body to make it vitrify and hold water at stoneware temperatures. We also found that we need to add small amounts of ball clay, sand, and silica to our clay body to be durable and make the glazes fit. This brings up an important and interesting question- how much do we tame a clay to meet our functional expectations, and how much do we adapt and learn from the beautiful (and limiting) qualities that drew us to the wild clay in the first place? PS Re Joseph's mention of Grogeewemee 10, here is a picture

These seem to be "wild" North Carolina clays (singly or as mixtures?). I've no idea if/where they might be bought, or how they might be approximated from commercial clays. Jeff makes a good point: if you are approximating the look of these clays then stains could simplify the process, especially if you wanted a palette of colours. From Wild Clay: The Story of NC Clay https://www.woodfirenc.com/wild-clay Sorry about the text size. Also see https://bandanapottery.com/materials Our main clay body… Our main clay body is mostly (75%) comprised of a mixture of two clays from our area: A coarse, red clay that is near our home in the higher mountains, and a more plastic grey clay that settled near a creek bed further down the mountain. We mix these wild clays into a slip and pour them through a screen into a large feed tank. The screening process is one of the first aesthetic and expressive decisions we make- the size of the screen determines the final landscape of particles in the clay beneath our slips and glazes. While dark in color, both these clays are so refractory in their pure state that we still need to add feldspar to the body to make it vitrify and hold water at stoneware temperatures. We also found that we need to add small amounts of ball clay, sand, and silica to our clay body to be durable and make the glazes fit. This brings up an important and interesting question- how much do we tame a clay to meet our functional expectations, and how much do we adapt and learn from the beautiful (and limiting) qualities that drew us to the wild clay in the first place?

Personally I doubt it's practical, but this at least tells you not to overheat it (see the last sentence in the quote). Might be worth a try in a domestic oven. https://en.wikipedia.org/wiki/Plaster Chemistry See also: Calcium sulfate § Hydration and dehydration reactions Gypsum plaster, gypsum powder, or plaster of Paris, is produced by heating gypsum to about 120–180 °C (248–356 °F) in a kiln:[18][13] CaSO 4 ⋅ 2 H 2 O ⟶ heat CaSO 4 ⋅ 1 2 H 2 O + 1 1 2 H 2 O ↑ {\displaystyle {\ce {CaSO4.2H2O {\overset {heat}{{}->{}}}{CaSO4.1/2H2O}+ 1\!1/2 H2O ^}}} (released as steam). Plaster of Paris has a remarkable property of setting into a hard mass on wetting with water. CaSO4⋅12H2O+112H2O⟶CaSO4⋅2H2O{\displaystyle {\ce {CaSO4.1/2H2O + 1 1/2H2O -> CaSO4.2H2O}}} Plaster of Paris is stored in moisture-proof containers, because the presence of moisture can cause slow setting of plaster of Paris by bringing about its hydration, which will make it useless after some time.[19] When the dry plaster powder is mixed with water, it rehydrates over time into gypsum. The setting of plaster slurry starts about 10 minutes after mixing and is complete in about 45 minutes. The setting of plaster of Paris is accompanied by a slight expansion of volume. It is used in making casts for statues, toys, and more.[19] The initial matrix consists mostly of orthorhombic crystals: the kinetic product. Over the next 72 hours, the rhombic crystals give way to an interlocking mass of monoclinic crystal needles, and the plaster increases in hardness and strength.[20] If plaster or gypsum is heated to between 130 °C (266 °F) and 180 °C (350°F), hemihydrate is formed, which will also re-form as gypsum if mixed with water.[21][22] On heating to 180 °C (350°F), the nearly water-free form, called γ-anhydrite (CaSO4·nH2O where n = 0 to 0.05) is produced. γ-Anhydrite reacts slowly with water to return to the dihydrate state, a property exploited in some commercial desiccants. On heating above 250 °C (480°F), the completely anhydrous form called β-anhydrite or dead burned plaster is formed.[19][22]

We seem to be talking at cross purposes. I was commenting on the use of sodium carbonate/bicarbonate for adjusting the rheology of a clay slip. While you seem to be adding sodium carbonate/bicarbonate to the surface of a pot then heating it: decomposing them to sodium oxide which eventually forms part of a "salt glaze". Min (with a like from Callie) commented on another thread How was your soda ash stored? If not kept sealed up in an air tight container it will change from sodium carbonate into sodium bicarbonate, which is a flocculant. ... and I was happy to take her/their word for it. PS This point has since amplified by quoting from http://www.marjonceramics.com/pages/Tips/slipmaking.htm Soda ash works to dissolve lignite in clay. ... I've no idea of the details of this mechanism, which sounds more complex than the simple addition of Na+ & CO3-- ions to the liquid. I've only got as far as https://patents.google.com/patent/US3325537A/en The humic acid content of lignite may be solubilized by treatment with alkalies, such as sodium hydroxide and sodium carbonate.

Are you sure?

You may be interested in (but not concerned about): Flambé Magic http://ceramicstoday.glazy.org/articles/flambe_magic.html John Britt investigates the appearance of mysterious crystals in the glaze slop.

You may find this of interest How to Increase or Reduce Crazing in a Glaze How to Adjust Crackle Without Changing the Overall Appearance of the Glaze https://ceramicartsnetwork.org/daily/article/How-to-Increase-or-Reduce-Crazing-in-a-Glaze

I find terra sigillata a confusing term, which is also often unrewarding to use in searches. Some of the issues are described in Terra sigillata https://en.wikipedia.org/wiki/Terra_sigillata The introduction is especially relevant, and I include the first paragraph of it. Terra sigillata is a term with at least three distinct meanings: as a description of medieval medicinal earth; in archaeology, as a general term for some of the fine red Ancient Roman pottery with glossy surface slips made in specific areas of the Roman Empire; and more recently, as a description of a contemporary studio pottery technique supposedly inspired by ancient pottery. Usually roughly translated as 'sealed earth', the meaning of 'terra sigillata' is 'clay bearing little images' (Latin sigilla), not 'clay with a sealed (impervious) surface'. The archaeological term is applied, however, to plain-surfaced pots as well as those decorated with figures in relief.

After some searching I found this paper. Which contains some though-provoking facts and ideas. Recovery and Revival of Attic Vase Decoration Techniques What can they offer archaeological research ? https://tinyurl.com/yecn6xnf Of course the firing (and final effect) of this "black gloss" is different from that of t-sig, but they both start by forming a "colloidal slip" (with or without the use of a deflocculant). p114 Gives the results of X-ray analysis of historic samples and modern "reproductions" - This clearly shows that the originals didn't use phosphorous-based deflocculants (many reproductions used calgol). - The "glaze" contains much lower calcium levels than the body. 118 It is pointed out that - The absence of phosphorous in the glaze implies that plant-ash deflocculants weren't used. - Although not conclusive the potassium levels suggest that potash defloculants weren't used either. p119 Looking for a deflocculant-free method of producing the "colloidal slip". - Using a low-calcium clay (similar to that used in antiquity) they found that they could get acceptable (deflocculated?) results a pH>8.7 and >15°C. - Using the same clay pre-soaked for six months they got similar (not-deflocculated?) results at pH~7 and >15°C. ... this suggests that slip production was a seasonal process, probably during the warmer spring to autumn. ... assisted by over-winter soaking of the clay. The difference in calcium content between different clays is shown in fig2 PS I couldn't help speculating: 1. That the need for low-calcium clay was because that any soluble calcium compounds would act as deflocculants. After all soluble calcium and magnesium compounds are used a deflocculants for glaze slips. 2. Historically they may have found suitable candidate clays simply by paddling round the local clay-pits in late spring, looking for signs of spontaneous colloidal dispersion. Those wishing to find suitable modern commercial clays may need to look at them after a 6-months soak.