PeterH

Are you thinking about measuring the contact angle? My knowledge of the subject ends with its name, but here are a couple of google hits: Contact Angle: A Guide to Theory and Measurement https://www.ossila.com/pages/contact-angle-theory-measurement ... which a least has some helpful pictures Simple Contact Angle Measurement using a Smartphone (Easy Guide) https://www.youtube.com/watch?v=s3DrTJk3CFA ... which tries to offer a half-way house between judging things by eye and the use of specialised equipment

Two trivial points. They sell water-repellent treatments for windscreens. I don't expect they are food safe, but they might give you an idea how useful a really water repellent surface would be on an experimental spout. Not too certain about this, but epoxy may have a lowish surface tension. IIRC people have mentioned food-safe epoxy in other postings. Typical values of surface energy for materials and adhesives https://www.twi-global.com/technical-knowledge/faqs/faq-what-are-the-typical-values-of-surface-energy-for-materials-and-adhesives May be true Food Safe Epoxy – Helpful Guide about Food Grade Epoxy https://resin-expert.com/en/guide/food-safe-epoxy PS I expect that the matt surfaces of super-hydrophobic substances would get clogged over time (BTW I live in a very hard-water area). How to Prevent Teapots from Dripping https://news.softpedia.com/news/How-to-Prevent-Teapots-from-Dripping-125869.shtml

Don't go there, these formula use the "particle density" rather than the "bulk density". See wiki for the full story: https://en.wikipedia.org/wiki/Bulk_density https://en.wikipedia.org/wiki/Particle_density_(packed_density) But imagine a quantity of sand. It's weight is easy, but what is it's volume? You can measure it in a measuring cylinder, getting a value for sand plus inter-grain air. Or you can pour it into a measuring cylinder already containing some water, and see how much the volume increases (avoiding measuring any trapped air).

What is (probably) important is that you add the bentonite in very small quantities, preferably sprinkled over a significant area. Then allow a little time before agitation, as you really want the bentonite to drop through the surface into the water of its own accord. IIRC the way it would be done in a lab is to place all the bentonite in a thin line on a glazed tile. Then cut small lengths off the line as required with a sharp edge (traditionally a razor blade).

I assume you mean Can you elaboration on your problems? After an initial abortive attempt, I re-read it's documentation* and then it seemed to work fine for me. Mwet = your weight of glaze in bucket = 2640 Swet = your measured specific gravity = 1.42 Sdry = Brongniart’s recommended value = 2.6 giving Mdry = weight of glaze powder in the bucket = 2640*(1-1/1.42)/(1-1/2.6) Plugging this into google gives 1268.9 again * As they say in software engineering, if all else fails RTFM (read the f-ing manual). A tribute to the the fact that much of the available documentation is often inappropriate or of poor quality.

And if all else fails there are "equation solvers" about which can perform some of the legwork, such as: Equation Solver https://www.dcode.fr/equation-solver Input 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) ... and ask it to solve for t gives you Only time I've had to use it so far was calculating the likely wall thickness of a Qvevra! ... and how sweet it still remembers the calculation for me.

I really hope it isn't necessary to try it, but I found this test method TECHNICAL NOTE -BENTONITE SWELL INDEX https://globalsynthetics.com.au/wp-content/uploads/2016/05/TECHNICAL-NOTE-SWELL-INDEX.pdf ASTM- D5890 is used to determine the swell index. A 2g sample of dried and finely ground bentonite clay is dispersed into a 100 ml graduated cylinder in 0.1g increments. A minimum of 10 minutes must pass between additions to allow for full hydration and settlement of the clay to the bottom of the cylinder. These steps are followed until the entire 2g sample has been added to the cylinder. The sample is then covered and protected from disturbances for a period of 16 - 24 hours, at which time the level of the settled and swollen clay is recorded to the nearest 0.5 ml. ... While the sodium bentonite clay utilized in Bentofix® GCLs typically meets a Swell Index in the range of 24 ml – 36 ml, the targeted minimum value is 24 ml /2 g. This minimum value will generally ensure the specified performance of a GCL product is achieved. Obviously 24-36 ml/2g = 60-90 ml/5g, and note (presumably active) dispersion of 0.1g increments. PS Should you try this -- and it gives an acceptable result -- maybe your bentonite is just extra difficult to wet. In which case using pre-slaked bentonite could be important helpful when making additions to your clay.

No I haven't used the calculator "in anger". It's not you maths, it's your modelling/physics that's leading you astray. IMHO it's a tricky and superficially misleading problem. After all a glaze is a "liquid" containing heavier-than water particles that aren't setting out (or at least only doing so slowly) and you don't meet too many of them. I've got a (very old) degree in maths & physics and still cannot just "see" what the formula should be, I have to go back to basics and start with: SG-of-glaze = weight-of-glaze/volume-of-glaze weight-of-glaze = weight-of-water + weight-of-glaze-powder volume-of-glaze = weight-of-water/SG-of water + weight-of-glaze-powder/SG-of-glaze-powder Once you can agree with that, the rest is just arithmetic. ... Or find a calculator to do it for you. Thank @Minfor the reference. PS Google makes quite a good calculator: enter 1371.1/1.0 + 1268.9/2.6 and you get ... I expect other browser do the same.

780 That's what the calculator gives me as well. SG of glaze 1.42, Weight of glaze in the bucket. Calculator gives weight of dry ingredients 1268.9g 5% of 1268.9 = 1268.9*5/100 = 63.444g stain ----------- So what's going on? First Brongniart's calculator gives results consistent with its model (glaze-powder is insoluble and has a typical SG of 2.6). Your figures are weight-of-glaze-powder= 1268.9, so weight of water = 2640 - 1268.9 = 1371.1 and SG = 1.42 Now volume-of-glaze = weight-of-water/SG-of water + weight-of-glaze-powder/SG-of-glaze-powder = 1371.1/1.0 + 1268.9/2.6 = 1859.1 So SG-of-glaze = weight/volume = 2640/1859.1 = 1.42 ----- Now you calculations gave weight-of-water = 1859, and weight-of-glaze-powder = 780 If this were true then ... volume-of-glaze = weight-of-water/SG-of water + weight-of-glaze-powder/SG-of-glaze-powder = 1859/1.0 + 780/SG-of-glaze-powder = 1859 + 780/SG-of-glaze-powder and SG-of-glaze = weight/volume = 2640/(1859 + 780/SG-of-glaze-powder) substituting SG-of-glaze-powder = infinity gives SG-of-glaze = 1.42 (the measured value) So the calculations you are performing assume that the insoluble glaze powder has an infinite SG (ie zero volume). Which obviously isn't true. -------------------- Double checking, if you apply the calculator with a stupidly high SG for for the dry ingredients it approaches you estimate for the dry weight.

terminological confusion? I think there is some terminological confusion here. When potters talk about stains they usually mean things like mason stains, which can be described as: Stains are dry powders made by firing selected oxides proportioned to produce stable crystals of consistent colour resistant to high temperatures and glaze attack. Ceramic stains are used to create coloured glazes, underglazes, and clays & slips.https://psh.ca/pages/mason-crysanthos-ceramic-glaze-stains (IMHO pigment would have been a much better choice of term, and seems to be what's used when describing paints or inks.) What you are referring to as a stain sounds more like an underglaze in potter-speak (or possibly a slip or an engobe). Underglazes are used in pottery to create designs and patterns that come up through the glaze covering them. This can give the surface more visual depth and character. Although they are often used under clear glazes, they can also be used under other, generally light-colored, transparent glazes. https://www.thesprucecrafts.com/what-are-underglazes-2746191 I'm definitely not saying your terminology is "wrong" in any sense. Just when talking about anything it minimizes confuse if we all use the same terminology. BTW I've used fairly random definitions plucked from the net, just to give an idea of their usage. @Min's suggestion that you post a picture of something close to what you are aiming for is a very good one, and the responses to it will help establish the the right pottery terminology (and products to use). PS A random selection of pictures of the craw glazes she mentioned at https://tinyurl.com/2865ec3z Ditto for reticulated glazes at https://tinyurl.com/yck9hmue ... but be warned some of them are difficult/antisocial to use/control (I remember one was described as "spits like an an orangutan in the kiln")

You want to use Brongniart's formula, which allows for the volume taken up by the (insoluble) glaze ingredients. You might start with http://www.potteryatoldtoolijooaschool.com/brongniarts_formula_made_easy.pdf ... a syringe is an easy way to measure specific gravity https://ratcitystudios.com/blog/2017/11/14/specific-gravity There is a calculate about https://pietermostert.github.io/SG_calc/html/brongniart.html

Interesting, but I don't think you need to buy it. Crushing Epsom Salts https://digitalfire.com/picture/2119 ... but I cannot see how it can take effect as quickly as the saturated epsom salt solution many recommend.

https://www.sciencedirect.com/sdfe/pdf/download/eid/1-s2.0-037851738490036X/first-page-pdf

I would love to read more about these processes. However it's worth mentioning that some beds of clays contain: natural deflocculants (eg humic acids & lignates) natural precursors to deflocculants (eg lignin) which are activated in alkaline environments (eg sodium carbonate). So it's quite possible that you could get a usable slip by careful selection of the clay used. (And a poor slip by modern standards would still be usable and open up a craft/industry). PS Off topic but well worth reading. A Secret of Chinese Porcelain Manufacture https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.196306971 The secret of old Chinese porcelain is the technique by which a material, capable of forming extremely thin-walled articles, was obtained from a slightly plastic kaolin. Intercalation compounds, which form by treating kaolinite with decaying urine, give the key to the preparation of this material. Unfortunately I cannot find a freely available copy at the moment, so from memory ... It seems that the Chinese eggshell porcelain industry was born when the amazingly plastic properties of a specific clay bed were discovered. It was found under the ruins of what had been a long-lived stable, and the properties were due to the action of stale urine on the kaolin particles. They then found out how to duplicate the effect under controlled circumstances. Basically kaolin occurs as platelets, which aggregate into stacks. Under suitable conditions the large stacks can be delaminated into smaller stacks or even individual platelets -- giving the body the "fines" necessary for plasticity. So in theory: ... and in practice:

The non-standard deflocculants are likely to give you a poorer quality casting slip, so why would you want try them before trying the industry/craft standard deflocculants? Genuine question, as I don't appreciate what's driving this decision (like the absence of supply chains or significant per-pot costs). Could you clarify what concerns you have with using the standard deflocculants? PS You may find this of interest Slip Casting - Alfred's Clay Store https://www.yumpu.com/en/document/read/34584429/slip-casting-alfreds-clay-store

I wonder if these ideas could simplify the incorporation of bentonite into the mix How to Add Bentonite to a Wet Glaze https://suemcleodceramics.com/how-to-add-bentonite-to-a-wet-glaze/

+1 Looking at @JolandavdG's web site: Book: Saggar firing in an electric kiln https://www.jolandavandegrint.com/book Some sample pages at https://tinyurl.com/23w3b8fc See https://tinyurl.com/473pcbpc as a guide to new & 2nd hand prices, changing the search to your location and currency ... also available in Dutch - revise search then change Book is written in to Dutch

Again, only the mildest of hints from Digitalfire. Formulating a body using clays native to your area https://digitalfire.com/article/formulating+a+body+using+clays+native+to+your+area -What might appear to be a worst-case scenario is that you find a fireclay. What good would that be for pottery? Fireclays are often just the crude form of ball clays. Slurry and screen and add about 30% feldspar and you have a cone 6 stoneware. A super plastic one.

Can anybody can provide a reference for this, or more details to aid my searches?. I did stumble across https://digitalfire.com/picture/1068 Also a tantalizing comment in https://digitalfire.com/glossary/stoneware PS I also found this of interest https://digitalfire.com/picture/c6Ho2e5Fsn

Tony Hansen https://digitalfire.com/material/vinegar

Fuller's Earth https://en.wikipedia.org/wiki/Fuller's_earth Fuller's earth is any clay material that has the capability to decolorize oil or other liquids without the use of harsh chemical treatment.[1][2] Fuller's earth typically consists of palygorskite (attapulgite) or bentonite.[1] Modern uses of fuller's earth include as absorbents for oil, grease, and animal waste (cat litter) and as a carrier for pesticides and fertilizers. Minor uses include filtering, clarifying, and decolorizing; active and inactive ingredient in beauty products; and as a filler in paint, plaster, adhesives, and pharmaceuticals.[1] It also has a number of uses in the film industry and on stage. Probably bad news, cat litter may often be calcium bentonite. See Digitalfire for the difference https://digitalfire.com/material/bentonite

I'm pretty certain its mainly zinc oxide with a little ferric oxide. Probably quite close to calamine powder BP (the 99.5% zinc oxide, 0.5% ferric oxide). After all it is a skin treatment with a long pedigree.

While waiting for knowledgeable replies ... From this picture of a casting table ... it looks like the main parts are * A table with rollers above the draining surface * A drain/holding tank * A tank stirrer motor and its propellers * A pump, hose and nozzle to move slip from the tank into the moulds You seem to have most of them. PS While the advantages of the table for mass-production look fairly obvious, I wonder if the cleanup overhead could become an issue for smaller batch sizes and/or lower throughput rates.

Have you tried an indian-ink test? Easy enough to wipe off if there are no cracks.

I think you misunderstand the point @Min was making. The artist she named must get their clay from somewhere, and perhaps they can help you get in touch with a supplier/source of pottery-grade clay.