PeterH

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
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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
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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.
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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.

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 

I suppose that it's just possible that some form of froth flotation is occurring, separating out some particles from the mix. It's certainly a technique widely used in mining/ore-extraction.
https://en.wikipedia.org/wiki/Froth_flotation
A hint that silicon carbide might be a candidate for this sort of extraction from silicon/silicates.

I see some of your text as white letters on a black background, so it's not just you.



an also generate this sort of text

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:

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
   

Hi goguma, 
Good question!
Opening the control board box, one should be very careful*!
There are several trim pots on the control board; is there one marked "ACCEL" (or ACC/DEL) ?
I haven't tried adjusting that one**.
If adjusting it does make the wheel rotation decrease faster, likely it will also make it speed up faster. 
ACCEL
setting determines the time the motor takes to ramp to a lower or higher speed.
 
*Read the documentation. Unplug the unit. Beware capacitors!
** see links posted by PeterH at the end of this thread:
Technical questions about the Skutt SSX controller - Equipment Use and Repair - Ceramic Arts Daily Community
see also: Wheel head takes almost 2 seconds to stop - Equipment Use and Repair - Ceramic Arts Daily Community
 
 

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

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

Given that it is probably overfluxed at cone 10 (references below) I would try a couple things. First I would fire some as is in the hottest part of your kiln and measure the porosity, it could just be low enough for your purposes as is. Will likely loose translucency but perhaps that isn't an issue.
If that is a no go then I would try adding 5% nepheline syenite to it. Coleman is so plastic I doubt this will make a significant difference to the working properties of it. 
From this link: 
From this link: 
"These are cone 10R porcelains made using Grolleg kaolin, feldspar and silica. Plainsman P700 (left) has 20% G200 Feldspar. Coleman porcelain (popular among potters in the US) has 30% of the same feldspar. The Coleman porcelain is certainly more vitreous. In fact, it is too vitreous. It is much more likely to warp during firing. And, it is much more problematic with regard to plucking (lower left), foot rings glue to even kiln-washed shelves. But, notice that the Coleman porcelain is not any more translucent than P700 (it appears less so because I could not throw it as thin). So why is 30% feldspar even used? I have a theory: American kaolins do require 30% feldspar to vitrify at cone 10, but not Grolleg. it contains significant natural feldspar, so much so that far less feldspar is needed in the recipe. I think that, in the past, Grolleg was simply substituted for an American kaolin a standard recipe. P700 benefits in a special way by recognizing this different in Grolleg: It dedicates the 10% gain to kaolin, increasing body plasticity. On top of that it adds bentonite, producing a porcelain whose high plasticity would come as a shock to people used to the Coleman body."
edit: I'll go through my bags of old clay and see if I kept any leftovers of Coleman, if I have some I'll  fire it to cone 6 electric and measure the porosity just for curiosities sake.
 

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

and that is how you know it is sodium bentonite: it swelled, became gelatinous. Calcium bentonite does not have that same reaction.
Tom

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

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 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.

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.
 
 

@suetectic grog is one thing: fired ceramic that’s been ground up to a sand like consistency. Temper is lots of things that can get added to a clay body to adjust it.

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.
 
 

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

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.

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?

@JimLurkinghi and welcome!
To add to what Peter said about terminology, all grog is temper, but not all temper is grog. Grog is clay that’s been fired and then ground into assorted sizes of grit. It can be added to clay bodies, or its used “off label” to large pieces on in the kiln to prevent cracking/warping/glaze getting onto shelves. North Americans tend to refer to the specific temper they’re using by name, whether it’s sawdust, paper pulp, chicken grit, decomposed granite, sand, etc. 
Temper is a term I’ve seen used more frequently in British or European references, or in archeological/art history writing. In those contexts, it’s a broad category that could mean anything from straw in adobe to river sand in assorted primitive firings, to chamotte, which is French grog from a specific clay.
 
(I will not make sparkling clay jokes, I will not make sparkling clay jokes, I will not make sparkling clay jokes)

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.