[determining weight of dry ingredients v. water in a glaze]

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 

[Low specific gravity but THICK!]

2 minutes ago, Pir said:

Interesting with Hansen describing how he gets a lower SG (1.43-1.45) and then flocculates. He uses epsom salt powder, which I haven't seen yet; I also haven't tried vinegar yet.

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.

[Alternative Deflocculants for Slip Casting]

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

[Alternative Deflocculants for Slip Casting]

On 11/12/2022 at 7:24 PM, Ryan M Miller said:

I have read that slip casting may have developed independently in China in the construction of early Jingdezhen pottery and in the construction of clay pan flutes in the first century of Peru (here) so alternative deflocculants must have been in use in these two independent locations in order to form a thick enough casting shell.

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:

[Alternative Deflocculants for Slip Casting]

On 11/12/2022 at 7:24 PM, Ryan M Miller said:

Before I do any tests with wood ash or tannic acid, I want to comfirm if any potters in this forum have ever used alternative deflocculants in slip-casting.

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

 

[Why my clay acts like this?]

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/

[Cone 6 Reduction Electric Kiln Firing in Saggars]

6 hours ago, Min said:

@bjorn.lindberg, I would send @JolandavdG a pm and ask them since they haven't been on the forum since March. Just click their name then at the top of the page that comes up click the little envelope and follow the prompts. They will get an email letting them know they have a message.

+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

[How to lower a cone 10 clay body to cone 7?]

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.

[How to lower a cone 10 clay body to cone 7?]

2 hours ago, Kelly in AK said:

Somewhere on Digitalfire Tony Hansen has written about combining two existing clay bodies to make a very nice stoneware, I just can’t recall the details. That could be a good resource. 

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

[Why my clay acts like this?]

35 minutes ago, Babs said:

I only mentioned vinegar because some very  experienced potter  mentioned it and I do use it  in my throwing water, makes it creamy. I also use it when attaching handles , or slabs. The chemistry I leave to someone else.

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

[Why my clay acts like this?]

1 hour ago, Tina01 said:

Does it have any other name? I can't translate it. Or what does it's made of?

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

[Calamine]

19 hours ago, jrgpots said:

Mine is the pink powder.   It is really hard to know exactly what it is!  I will calcine about 500 GM of the stuff and see what happens.  I will compare it to Zn oxide in a side by side recipe  with the calamine.  Maybe opacity a celadon  and see it there is a color change because of the Fe.

Jed

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.

[Slip casting equipment question]

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.

[Any ideas why these mugs look streaky after holding liquid?]

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

[Why my clay acts like this?]

10 hours ago, Tina01 said:

Thank you so much! this was a great favor, I'll contact him for sure if needed. but from my past experience in arts, generally speaking it's more likely to get scientific answers from the internet, that is most "masters" try to dictate what they have learned and never doubt on their teachings, whether there might be better and more correct approaches available. 

Again, thank you, your time and effort are greatly appreciated.  

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.

[Calamine]

5 hours ago, jrgpots said:

Fe2O4Zn is what pubchem quotes it to be. 

Don't you just love it when they overload an already overloaded name.

Personally I find the Pubchem page https://pubchem.ncbi.nlm.nih.gov/compound/Calamine massively confusing as it gives Calamine lotion as a synonym. At least here in the UK Calamine lotion BP (British Pharmacopea) is zinc oxide with 0.5% ferric oxide -- and has been at least since at least the 1950s when it was widely used to treat sunburn. 

Anyway, what colour is the stuff you have? American Elements https://www.americanelements.com/zinc-iron-oxide-12063-19-3 give Fe2O4Zn as Zinc Iron Oxide (aka Zinc Ferrite) a brown solid.
There is a picture at https://www.funcmater.com/zinc-iron-oxide-znfe2o4-powder.html

While calamine powder BP (the 99.5% zinc oxide, 0.5% ferric oxide stuff) is decidedly pink
https://m.jppharmaglobal.com/calamine-powder-bp-5307563.html

While both pure zinc carbonate and pure zinc silicate are white
 

[Calamine]

33 minutes ago, jrgpots said:

Calamine is Fe2OZn. 

Are you certain, and can you give a reference?

Wiki gives two definitions of calamine, for a medication and a mineral.

As a medication https://en.wikipedia.org/wiki/Calamine
Calamine is a combination of zinc oxide and 0.5% ferric oxide (Fe₂O₃).

As a mineral https://en.wikipedia.org/wiki/Calamine_(mineral)
During the early 19th century it was discovered that what had been thought to be one ore was actually two distinct minerals:

• Zinc carbonate ZnCO₃ or smithsonite and
• Zinc silicate Zn₄Si₂O₇(OH)₂·H₂O or hemimorphite.

PS Searches for calamine clay were largely uninformative, although this one for Calamine Powder says it is also known as hemimorphite (i.e. zinc silicate).
https://www.thesoapkitchen.co.uk/calamine-powder
... and then gives a safety data sheet for 99.5% zinc carbonate and 0.5% ferric oxide!

[Why my clay acts like this?]

15 minutes ago, suetectic said:

So now I wonder if the 'grit, sandstone, limestone, igneous rock' are considered temper because they are not 'tempered'?

Not the way I read it, I think it's the clay/body that is tempered.

https://dictionary.cambridge.org/dictionary/english/tempered
tempered (adjective): limited or controlled, or made less extreme.

So you achieve  a tempered clay by adding temper to a less manageable one.

From Hamer & Hamer
Temper. An addition to clay which improves work-ability, e.g. sand and grog. Temper will also affect the fired result but it's introduction is essentially to assist forming and uniform drying.

 

 

[Why my clay acts like this?]

19 minutes ago, suetectic said:

I'm curious as well what an example of temper not grog is.

This gave 12 examples of types of temper, only one of which is grog.
Temper (pottery) https://en.wikipedia.org/wiki/Temper_(pottery)

[Runny casting slip]

20 hours ago, Min said:

With all due respect it can't be 95 grams. 100ml of water weighs 100 grams. Every material added to the water in casting slip has a higher specific gravity than water. Your friends 1.75 makes sense, perhaps they could use their scales for you and weigh some out?

Can you repeat your measurements of SG -- for both the slip and just water -- and report your raw data as well as your calculated SG.

Making measurements for two liquids may help us discover where the error is occurring.

[How to control blurring of oxide under glaze or over glaze decoration?]

45 minutes ago, Franny said:

When I mentioned using matcha tea as a medium for mixing oxides I couldn't remember where I'd seen that reference - or rather it was in an Instagram post that I now can't track down.  But I came across this on Richard St John Heeley's website http://www.richardheeley.com/index.html/blue_%26_white.html :

‘Gosu’ is the Japanese name for natural cobalt. The ground cobalt powder was traditionally applied with a thick green tea solution that had been boiled down to a syrup. This mixture would be combined with the ‘Gosu’, enabling it to be applied freely and smoothly during painting. It was allowed to dry and then glazed. The tannin in the tea kept the decoration from spreading when the glaze was applied.

Interesting!  Don't you just love chemistry?!! I sense a google rabbit hole search of 'tannin' may be on the cards!!! Happy days

I have a faint memory of stale 7-up being used as a medium by some Japanese potters.

OILS AND MEDIUMS  http://www.porcelainpainters.com/mediums.htm
Sugar
There are numerous recipes for sugar solutions to be used for pen work and for painting. The most common and easy medium is regular 7-Up. Everyone who paints or draws with sugar solutions seem to have their favorite mixture. The most common recipe is made by boiling 2 parts water with 1 part sugar, and using the syrup as a painting medium or thinned for pen work. It dries quickly and requires practice to gain consistency in brush work.

[Why my clay acts like this?]

Maybe of interest ...
Temper (pottery) https://en.wikipedia.org/wiki/Temper_(pottery)
A temper is a non-plastic material added to clay to prevent shrinkage and cracking during drying and firing of vessels made from the clay.
... and goes on to list 12 types

I don't know how useful this definition is, or how widely it would be accepted.

Note that the definition doesn't cover the use of  "combustibles" such as coffee grounds or expanded perlite to add texture to the fired surface.

Are there any additions to a flameware body purely to modify the fired thermal properties, rather than the shrinkage/cracking of the body during drying and firing? [Mica might be one?]

 

PS It doesn't pass modern  health & safety requirements -- and it has nothing to do with your questions -- but have you heard of  Obvara Raku? Which I believe has it's origins in sealing porous cooking vessels.

Marcia Selsor's Tips on Obvara Firing
https://ceramicartsnetwork.org/daily/article/Marcia-Selsors-Tips-on-Obvara-Firing
The obvara firing technique is a technique originally used to seal low fire pottery. It is believed to have originated in Eastern Europe during the Middle Ages.
 

 

 

 

 

[China Painting base recipes and starting points]

7 hours ago, Kelly in AK said:

Lewing’s book, China Paint and Overglaze, 2007, is also available to check out on the Internet Archive (a legitimate library, you have sign up/in and can check out books digitally). 

https://archive.org/details/chinapaintovergl0000lewi/mode/1up

Looks like a nice book.

A few sample pages available on amazon: https://tinyurl.com/mvayyb3f

It looks like even 2nd hand copies are fairly pricey (change search to your location & currency):
https://tinyurl.com/mr2wr7be

[Why my clay acts like this?]

In case it's of any help: Clays of Georgia for Ceramic Applications
http://gspltd.ge/admin/editor/uploads/files/InterCeramics.pdf

No experience in looking for clay myself, but perhaps these are of interest:
Where is Clay Found? https://ancientpottery.how/where-is-clay-found/
How to Find Clay, the Definitive Guide  https://ancientpottery.how/how-to-find-clay/

But if you do have a commercial source of real pottery clay, that seems the easiest option. Even if you have to re-hydrate it.

[Slipcasting with Paper Clay]

You may find the results of a search for flameware in the Clay and Glaze Chemistry forum of interest.