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Member Since 29 Jul 2010
Offline Last Active Jan 22 2014 02:28 AM

Topics I've Started

Keeping Record of your work Part VI

14 January 2013 - 09:00 AM

The major aim of my posts in this series is to emphasize on keeping records of all what you in the studio. I can assure you this is extremely helpful to learn and to increase ones experience.
The posts started somewhat 'upside -down' with the intention to show that there is more than just keeping track of a recipe or a firing. Nevertheless, I repeat that everything related to your work is worth to be recorded.
I use Filemaker Pro as the database system. For sure, there are other means. It depends what is useful and available for you.
I try to put a screen dump of the main page (layout: 'Full Info') here. It is very big window and I need to scroll to see everything. The picture may by this be of low quality, sorry for that.

The best is that I give a breakdown what fields are used and what they contain per record. Each record contains the full information of one ceramic piece. Fortunately, Filemaker allows to make different layouts, so that one can obtain a customized window with less cluttered fields.

Fields Content

Bisque number: I use unique numbers for each piece. The format is: yymmdd plus a suffix for each object of that day.

Firing date: The date of the glaze firing

Clay: The type of clay used

Slip: The type of slip used if any

Glaze: The glaze code

Kiln type /program : Gas kiln or electric (with ramp program n°)

Atmosphere : Oxidation or Reduction

Reduction from : Temperature at which the reduction is started

Glaze T°: Cone number at which the glaze is fired

Cone T° range : If any, the temperature range in which glaze can be fired

Re-fired : If the piece had to be re-fired: date

Type: Earthenware, Stoneware, Porcelain, Raku

Object description : Brief description of the ceramic object

Glaze remark : Remarks on glaze: faults, appreciation...

Original comment : If the glaze came from a book or elsewhere: the comment of the author

General : General comment on the object: esthetics, faults, intended use, ...

Source : Reference to the article or book where the glaze came from

Score : (for fun) number of stars as appreciation from 0 (= destroyed) to 5 stars

Glaze recipe (box): The glaze recipe with the colorants added separately

Picture: Picture of the object

Detail : Macro picture of glaze detail

Firing diagram : As shown in part I

Si/Al plot : As shown in part II

Ternary plot : As shown in part III

Limit graph : As shown in part IV

Thermal expansion graph: As shown in part V

INSIGHT Data general : Si/Al, SiB/Al, thermal expansion, LOI, ...from INSIGHT

INSIGHT Chemistry : Unity formula, Limits and Molar %

Further, there are knobs and links to shortcut to other layouts, databases ...
Several fields contain drop-down menu's for easy completion.
For multiple glazes applied on the object, tabs are provided to show the respective recipes

My database contains over 500 records today.

I hope this all helps to keep things organized and is helpful to increase the potter's experience.

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From Wikipedia:

Hermes was a god of transitions and boundaries. He was quick and cunning, and moved freely between the worlds of the mortal and divine, as emissary and messenger of the gods,[1] intercessor between mortals and the divine, and conductor of souls into the afterlife. He was protector and patron of travelers, herdsmen, thieves,[2] orators and wit, literature and poets, athletics and sports, invention and trade.[3] In some myths he is a trickster, and outwits other gods for his own satisfaction or the sake of humankind.

So, girls and boys, think what you like...

.... and....

For more information on glaze chemistry, visit my pages at:


Keeping Record of your work Part V

14 January 2013 - 05:35 AM

This time I will write a bit on the thermal expansion of glazes.

The main causes of crazing and shivering are in the thermal expansion of glazes not being in equilibrium with the fired clay used.

In the case of crazing, the glaze contracts more than the clay upon cooling and 'breaks' when the tension becomes too high.

In the case of shivering, the reverse occurs and the glaze becomes 'to big' for the clay and splits off from the fired clay body. This can occur sometimes long after cooling, up to years.

Obviously, the aim is to mix glazes so that their thermal expansion is in equilibrium with the fired clay. Again here, the book of J. Hesselberth and R. Roy ( Mastering Cone 6 glazes) is the reference for further reading. The authors spent quite a long article on this topic with plenty of practical experiments. How they measure thermal expansion is not meant for day by day potters but gives a good scientific proof for how glazes should be made up.

As an important factor for the glaze quality and as an aid to learn more in the future, I use this parameter in the documentation of my ceramic work.

Again, by the use of a glaze calculation software, the values for thermal expansion can be obtained. Also again, this can be obtained by calculating by hand, provided that one has the thermal expansion coefficient for each ingredient.

The graph at the end of the text is a bit hybrid this time. It combine Si/Al ratio and thermal expansion. It also contains SiB/Al ratio. Boron has an exceptional behavior in glazes. In the unity formula it is grouped under Amphoteric but, it act as a glass former too. This makes it more complex. The SIB/Al is less a good indicator for gloss. I should maybe write: 'for matt' . The power for Boron to 'dissolve' Alumina is enormous. So, more glossy glazes are to expect.

Some authors tend to classify Boron as a flux or as a glass former also.

I keep the traditional Seger (unity) formula where Boron is an amphoteric (sometimes called: stabilizer). Although I am using Boron for ages in my glazes, I am still learning how to tackle its mechanism. Therefore, I keep record of the SiB/Al to gather data before drawing conclusions.

Michael Bailey spent a whole chapter on the use of Boron in his book: 'Glazes Cone 6' (Ceramic Handbooks, A&C Black -London)

To construct the bar chart, you obviously need the aforementioned parameters from a glaze calculation software or calculated by hand.

We are coming close to the end of this series. Next time I will discuss how to put everything together in a database for documenting ones work.

Visit my website for more on glaze chemistry:

http://users.telenet...amics menu.html

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Keeping Record of your work Part IV

12 January 2013 - 05:36 AM

In the previous post I treated the plotting of Fluxes, Amphoteric and Glass formers as a help and as an item to document ones work.

With a little exaggeration, I can put that there are as many limit formula as there are authors on the subject. I stick to those mentioned by J. Hesselberth and R. Roy in their book "Mastering Cone Glazes". This range of limits is also available in the INSIGHT and other glaze calculation software.

What is the use of these 'limit formulas'? As J.H. & R.R. put it: they are useful as guidelines, to make 'stable' glazes with the remark that one can make stable, good glazes who are way out of the limit formula.

My definition of a 'stable' glaze is a glaze that:
  • Has no glaze flaws like: crazing, shivering, crawling or dunting
  • Is food safe when required
Limit formulas can help but are not the universal panacea.

Herewith the J.H. & R.R. Limit Formulas. They give the range of moles in the unity formula for the different oxides:

Oxide range (Seger Unity) J.H & R.R.

K+Na2O 0.1 - 0.3
CaO 0.2 - 0.6
MgO 0 - 0.3
BaO 0 - 0.4 (Cooper & Royle)
ZnO 0 - 0.2
SrO 0 - 0.2
Al2O3 0.25 - 0.5
B2O3 0 - 0.3
SiO2 2.5 - 4.0

What you need is just the transformation of your recipe into the Seger unit formula. In glaze calculations software the limits are given next to it.
So you don't need to make graphs, but I do. Graphs are more meaningful to me than just figures. It is a personal preference.
In the example at the end of the text, SiO2 is divided by 10 to keep the graph in good proportions. The red marker lines show the limits.
The glazes MC6G 1 and MC6G 2 are way out of limits for CaO and below limits for the alkalis. These are nevertheless reputed stable glazes. One can here also conclude they are Alkaline Earth matts.

I document all my work with the topics mentioned in these posts, past, present and future.

I repeat: For information on glaze chemistry, visit my website at:

Next time I will discuss briefly thermal expansion and its role in glaze flaws.

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Keeping Record of your work Part III

11 January 2013 - 05:56 AM

In the previous post I discussed briefly the value of plotting Si/Al ratio in order to predict -with some reserve- the appearance of glazes. This time I like to show an example of a ternary or tri-axial plot based on the molar % of the glaze formula (in the analysis %).

The reading of this kind of plot requires a bit of reflection but once figured out, it again adds interesting information on the glaze(s).

The capability to predict the glaze appearance is somewhat less accurate than with the Al/Si plots, especially when Bore is used in the formulation. On the other hand I find that from scientific/technical viewpoint it helps to understand glaze chemistry.

What you need is molar % of the used elements. If you have a recipe, you can calculate this by hand but, this is rather tedious. A glaze software like INSIGHT can give it in 1 or 2 clicks. Then the different Mol% of the metals are grouped in Fluxes, Amphoterics and Glass formers. When % are calculated for each group, these values can be entered in the ternary plot template.

The template to make ternary plots is rather complex. I can provide it on request.

An example is at the end of the text.

In the example, WWW172 is likely to be a matt glaze, WWW390 has to rated as satin-matt and the other 2 glazes are probably glossy.

Next time I will discuss the relative importance of limit values for the common elements used in glazes.

We are still quite far away of 'putting things together ', be patient! In a few more posts to come, it will be revealed.

For information on glaze chemistry, visit my website at:


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Keeping Record of your work Part II

10 January 2013 - 11:14 AM

In the previous part, I explained the value of keeping record of all parameters in your ceramic work. The example given of a firing diagram is particularly valuable to master your kiln, especially if, like me, you use a simple, manually controlled gas kiln. Combustion kilns can be very 'moody' and therefore these recordings help you to get acquainted with your kiln.

This time, I will briefly discuss and show one aspect of the glaze chemistry.

Michael Baily's very interesting book "Glazes Cone 6" ( A&C Black -London / University of Pennsylvania Press) inspired me to adopt his viewpoints to predict the appearance of a glaze.

From the unity formula, the (molar-) quantities of different ingredients expressed as oxides can tell you a lot.
However, to make life easier, it is often sufficient to plot the Si/Al values in a graph and from where the plotted points appear, to obtain a good idea how your glaze may look.

I am a chemist, but you don't need deep chemistry knowledge to make the graphs and to interpret them. The only thing you need is the Unity Formula or only the Alumina and Silica molar parts.

In the example given here, one will discover that glaze B 123 is definitely an Alumina matt. Glazes B 210 and B 186a will be Alkaline Earth matts or, especially B 186a a satin - High Alkaline Earth matt. In turn, glaze B 215 will probably be a glossy gaze - on the edge of being satin.

One has to be aware that those readings are approximations, as a lot will depend on how they are fired. Long or short holding periods, steep or flat heating curves, accidental reduction and many others may alter the results.
Keeping this information for each ceramic piece you make will help you to refine your work.
I recommend to go to my website and push the button 'Chemistry Ceramics'. It is a good introduction to ceramics and about its chemistry.

(It is a quite big PowerPoint presentation)


In Part III, I will briefly discuss Ternary graphs of Fluxes, Amphoteric and Glass formers.

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