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Egyptian Faience - Was The Paste Too Old?


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Hello all. 

 

I put my Egyptian faience pastes into action yesterday and using my kiln for the first time. I was wondering if anyone could give some advice. 

The paste I fired was around two months old, and I left them dry for a total of 72+ hours while they create an efflorescence crust. My pieces were fired for around 6 hours, and I dropped the temperature from 900-700 degrees three times to allow the alkaline to fuse. However, the glaze on my piece did not come out as thick as expected. I think this is because the paste was not "fresh" and because I left it dry for too long. Most of the moisture left the piece which meant that this hindered the glaze. (please see image 1). 

 

I'm not sure if any of you are familiar with Egyptian faience. So I will attach some photos with this. 11123748_836159059790111_970016135_n.jpg


The attached image of the necklace is Egyptian Faience - however which a much thicker glaze. 

Any opinonios/advice would be awesome, thank you :-)

I am trying to prepare for my attempt 2. This is a project I am doing with my University, so there are time constraints on the amount of experimentation I can carry out. 

post-66411-0-33690300-1428658508_thumb.jpg

post-66411-0-33690300-1428658508_thumb.jpg

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Where are you getting this firing cycle from? Seems odd to drop the temperature three times to 700.

 

They look quite close to me but underfired. If when the pieces dried they did create an efflorescence crust then I think there may be nothing wrong with using old paste. How are you making the paste?

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Where are you getting this firing cycle from? Seems odd to drop the temperature three times to 700.

 

They look quite close to me but underfired. If when the pieces dried they did create an efflorescence crust then I think there may be nothing wrong with using old paste. How are you making the paste?

Because of my equipment I could not control the temperature. I could only read it and change the dial of my infinity switch. These pieces were fired at a total of 6 hours out of the 9 hours, I stopped this at 6 hours because they looked like they were about to crack. Also, they had not changed a lot from 4 hours in. I started to fire them at 900 and every hour, I dropped this temperature and then put the temperature back up again. 

 

CHEMICAL

FORMULA

PERCENTAGE

VOLUME

SILICA

SiO2

87%

90g

SODA ASH

Na2O3

4%

4g

WHITING

CaO

4%

4g

COPPER OXIDE

CuO

0.5-1%*

1g

BALL CLAY

--

4%

4g

WATER

H2O

*

20ml

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So you are starting at 900 deg and then dropping the temperature to what every hour? Where did you get the idea to do this?

 

If you were to plot the temperature on a graph what would the line look like?

 

This is what most ceramic firing curves look like, a slow rise up to the top temperature with a hold and maybe controlled cool back to room temp.

95273.jpg

 

 

If you stored the paste in dry state it shouldn't go to old.

 

Your chemical composition has quite small amount of soda. I'm using similar composition but with soda ash  about 8-12%.

 

Figures on your picture looks to me underfired,

 

How do you fire your paste?

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So you are starting at 900 deg and then dropping the temperature to what every hour? Where did you get the idea to do this?

 

If you were to plot the temperature on a graph what would the line look like?

 

This is what most ceramic firing curves look like, a slow rise up to the top temperature with a hold and maybe controlled cool back to room temp.

95273.jpg

 

 

If you stored the paste in dry state it shouldn't go to old.

 

Your chemical composition has quite small amount of soda. I'm using similar composition but with soda ash  about 8-12%.

 

Figures on your picture looks to me underfired,

 

How do you fire your paste?

 

800 - 850 C with 30 min hold at 500 and  30 min hold  on top temp.

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Below are some recipes I found online. Just from scanning and no true knowledge( I am a beginner) , you might not have enough soda in there for it to act as a flux or melter. You don't need to keep going up and down with temperature. You do need to get a temperature that melts the ingredients. Weird ( to me) thing about clay is a lot of the ingredients have a very high melting point on my here own, but if some of another ingredient is added, it melts at a much lower temperature.

 

Egyptian paste recipes very somewhat. Generally, about 60% of the body will be non-plastic material; there will be at least 10% of a sodium-bearing material such as soda ash, bicarbonate of soda, or borax; and there may be up to 20% clay. Basic Egyptian Paste

Ball clay 20

Soda feldspar 35

Silica 35

Sodium carbonate 10

*** Egyptian (turquoise) blue: 3% copper carbonate

EUP Egyptian Paste

Soda feldspar 38

Silica 38

Ball clay 12

Soda ash 6

Sodium bicarbonate 6

*** Egyptian blue: 3% copper carbonate

*** Blue: 2% cobalt carbonate

Egyptian Paste II

Soda feldspar 38

Silica 19

Kaolin 13

Ball clay 5

Sodium bicarbonate 6

Soda ash 6

Calcium carbonate 5

Silica sand 8

*** Egyptian blue: 3% copper carbonate

*** Blue: 2% cobalt carbonate

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I noticed something in the OP's formula that is going to mess with the advice everyone is offering: the OP is measuring by VOLUME, and we all assume weight measurements, because that's ceramic standard. 4% soda ash by volume will look like a different animal than by weight.

 

But I agree that the pieces are likely under fired, and heating and cooling it the way you describe seems highly unnecessary. Re-fire the existing pieces by gradually turning up the heat once an hour or so, being very careful around the Quartz inversion point. Hold until the glaze looks smooth and shiny in the kiln and cool slowly. Ancient Egyptians didn't have Orton Pyrometric cones, they probably fired by eyeball, too.

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I noticed something in the OP's formula that is going to mess with the advice everyone is offering: the OP is measuring by VOLUME, and we all assume weight measurements, because that's ceramic standard. 4% soda ash by volume will look like a different animal than by weight.

 

 

 

Good point,  but, soda ash is 4% and 4g in 103 total. Question is,  what is the correct value.

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To me it looks like they are using the term volume for weight. Weird xD

 

CHEMICAL FORMULA PERCENTAGE VOLUME

  SILICA           SiO2                87%            90g

 

 

Anyway, whatever the recipe it is close to other paste recipes, right? Concentrate on sorting out the firing first.

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Where are you getting this firing cycle from? Seems odd to drop the temperature three times to 700.

 

They look quite close to me but underfired. If when the pieces dried they did create an efflorescence crust then I think there may be nothing wrong with using old paste. How are you making the paste?

Because of my equipment I could not control the temperature. I could only read it and change the dial of my infinity switch. These pieces were fired at a total of 6 hours out of the 9 hours, I stopped this at 6 hours because they looked like they were about to crack. Also, they had not changed a lot from 4 hours in. I started to fire them at 900 and every hour, I dropped this temperature and then put the temperature back up again. 

 

 

AFAIR she is using small kiln for metal clay without controller, so it'll be hard to make reasonable firing.

 

@sparklingmango

 

How big are those item on photo ?

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Ok, I shall try and reply to all! 
 
Sorry I'm an Egyptologist, so I am not very good with this chemistry/ceramics shizz, so you'll have to bare with me :P 

Volume = weight

It was my first time firing, so this was an experiment if anything. Here I will attach a link of a table I created of the firing pattern. Please see for more info. It was stopped with 3 hours left. (hense why it doesnt go to the end...)

Yes, in the Egyptian recipes they did use some sort of clay. I got this recipe from a PhD Dr who is an expert in Egyptian Faience so I know that pretty much it is correct. Plus, the first firing following this came out pretty well for my first time so I think I am on the right track here atleast. ?? 

 

If you want to see more about recipes please see Paul Nicholson or Pamela Vandiever.

 

Fortunately,  I have my own kiln so this week is going to be a lot of experimenting to find a good firing cycle for faience. 

Tomorrow I plan to do some experimentation with the firing cycles. Like David said I am going to try and hold the higher temperature rather than drop it. Although, because the pieces were underfired (it is hard to see in the pic) but it looks like they were pretty much on there way to getting a good glaze.

 

TIME REMAINING

TEMP

DIAL NO.

NOTES

8 hrs, 35 mins

935 °C

8.5

 

8 hrs, 16 mins

816 °C

5.3

 

8 hrs, 4 mins

789 °C

5

 

8 hrs, 1 mins

 

1

First drop down hour to 100 °C

7 hrs, 46 mins

585°C

1

 

7 hrs, 33 mins

474°C

1

 

7 hrs, 25 mins

405°C

1

 

7 hrs, 5 mins

312°C

1

 

6 hrs, 51 mins

260°C

1

 

6 hrs, 37 mins

626°C

8

Turned dial back up to 8

6 hrs, 7 mins

880°C

8

 

5 hrs, 52 mins

917°C

8

Dropped down to 7 dial to maintain suitable temperature

5 hrs, 36 mins

905°C

7

Dropped down to 6.8 dial because temperature was too high

5 hrs, 27 mins

873°C

6.8

 

5 hrs, 16 mins

865°C

6.8

Dropped down to dial 6 to maintain faience temperature

5 hrs, 7 mins

838°C

6

Dropped down to dial 2 to start the second cycle of cooling down

4 hrs, 56 mins

732°C

2

 

4 hrs, 43 mins

599°C

2

 

4 hrs, 30 mins

511°C

2

 

4 hrs, 19 mins

459°C

2

 

4 hrs, 9 mins

417°C

2

Dropped to dail 1 for a lower temperature

3 hrs, 49mins

309°C

1

Changed dial to 7 to get a higher temperature

3 hrs, 38 mins

508°C

7

 

3 hrs, 20 mins

693°C

7

Changed dial to 8 to get a higher temperature

Thanks for all your advice dudes. 

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That sure is the craziest firing I have seen. You went room temperature to 900degC in 25 min! There is no way you need to be dropping the temperature, or getting to 900degC in 25 min. Who told you to fire this way?

 

What do you mean when you say 'maintain faience temperature' What is faience temperature?

 

 

I would think a firing cycle would be something like this. Seeing as the clay can take being heated up fast in 25 min I think you can easily shorten your 9 hour firing cycle.

 

0-1 hours on setting 1.

0-2 hours on setting 4.

0-1 hours on top setting till you reach top temp.

Hold temp for half an hour

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That sure is the craziest firing I have seen. You went room temperature to 900degC in 25 min! There is no way you need to be dropping the temperature, or getting to 900degC in 25 min. Who told you to fire this way?

 

What do you mean when you say 'maintain faience temperature' What is faience temperature?

 

 

I would think a firing cycle would be something like this. Seeing as the clay can take being heated up fast in 25 min I think you can easily shorten your 9 hour firing cycle.

 

0-1 hours on setting 1.

0-2 hours on setting 4.

0-1 hours on top setting till you reach top temp.

Hold temp for half an hour

hahaha i know right, it is crazy!! 

 

I was told to do 900 degrees and then drop to cool down at 100 degrees, but i dont really know what that meant. 

 

so, i just went a bit crazy with the first attempt to see what it would turn out like. my main objective was to get up to around 900 degrees and then just slowly drop it down and bring it up again, i have recorded it so much because i do not have a controller and for future reference (too improve the firing cycle!)

 

ok, awesome, i shall try this way. i was hoping to create something like that, i just need to experiment more. 

 

I shall let you know how the next one goes, hopefully with less crazy and more glaze! 

 

 

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That sure is the craziest firing I have seen. You went room temperature to 900degC in 25 min! There is no way you need to be dropping the temperature, or getting to 900degC in 25 min. Who told you to fire this way?

 

What do you mean when you say 'maintain faience temperature' What is faience temperature?

 

 

I would think a firing cycle would be something like this. Seeing as the clay can take being heated up fast in 25 min I think you can easily shorten your 9 hour firing cycle.

 

0-1 hours on setting 1.

0-2 hours on setting 4.

0-1 hours on top setting till you reach top temp.

Hold temp for half an hour

I kind of used your firing cycle. I modified it a bit though, 0-1 hours to 1 then 2, 0-2 hours to 6 and then 7. high temp then cool down. Total firing 5 hours and a half

 

here are the results, much better than the first :)

post-66411-0-27162900-1429115443_thumb.jpg

post-66411-0-27162900-1429115443_thumb.jpg

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Great :D They look much more glassy. The bigger figure looks a little dull so it could be worth trying next time to go even slower through the last 100 deg of temperature rise to get the heat into the bigger pieces. Most of the melting will take place here and if you go too quick things don't get enough time and temperature to melt.

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  • 4 years later...

Some rely on colour (red -> orange -> yellow -> white ...ooh, that's hot!) only, even today in the "...fascinating modern age we live in." - and do quite well with it (be sure to wear appropriate eye protection!! !!! !!!!).

Me, well, I'm watching the thermocouple readout an' pyrometric cones.

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2 hours ago, Briantllb said:

do you guys seriously thing the ancient Egyptians had kiln controllers?

No, they had hundreds of generations of trial and error passed on from father to son.  That's way better than a kiln controller.  Unfortunately most of the potters I know only have the one lifetime to achieve what they need ;)

Plus when firing with wood, you are the kiln controller ;). We can.try to mimic the variation and hurdles involved with fuel firing by manipulating our controllers.

Edited by liambesaw
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mango,   now that you are on the right track, may i suggest something else? 

your necklace has a good line (design) from right to left and back again EXCEPT for the one piece that dangles to a point.   that one should be in the center to balance the whole arrangement.

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