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Hermes

Keeping Record of your work Part II

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Hermes    0

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)

 

http://users.telenet...ics%20menu.html

 

 

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

 

 

 

B%20123%20186a%20210b%20215%20SiAl.jpg

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Marcia Selsor    1,301

Thanks for posting the chart. I recommend Michael Bailey's ^6 Glaze book too. The concept of how Alumina /silica ratio influences the surface texture is a basic in understanding glazes.

 

 

 

Marcia

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