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Glaze Stoneware Or Earthenware?

Glaze stoneware earthenware

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#1 Celia UK

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Posted 21 July 2014 - 03:49 AM

In amongst a batch of ceramic materials & equipment I bought from a potter who was going travelling are two buckets of mixed, liquid glaze. One is a 'matt turquoise blue' the other 'black'. This was a hurried purchase as the young lady was leaving the country the following day and I'd already taken up an hour of her time sorting through her garage! She told me that the black was very runny, and to be careful, and it is labelled as such. I don't know if these are earthenware or stoneware glazes, they were her own mixes. A couple of questions. ( I do plan to test, test, test. ) I currently use a smooth white earthenware, fire in a small electric kiln., glazes usually to 1060/1080oC

1 - what will happen if they are stoneware glazes and I use them on white earthenware firing to earthenware temperatures.

2 - as I already know the black is runny, other than only using it on a rim and expecting it to run, is there anything I can add (without having any idea of the original recipe) that will make it less runny?

3 - what would happen if Earthenware is fired above the recommended temperature? E.g. If I bisque an earthenware piece to 1000oC then glaze to a stoneware temperature?

Many thanks, in anticipation.

#2 Min

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Posted 21 July 2014 - 06:09 AM

1 - stoneware temp glazes fired to earthenware temps will be underfired, rough, unmelted. This would be a no go.

 

2 - runny is very nice when used in the right way. To stiffen it up you would add alumina, kaolin is a good source of alumina. Since you are working with wet glaze I would weigh out 200 grams of well mixed wet glaze then add 2 grams of kaolin, dip a test tile, add another 2 grams, dip another test tile and keep going until you get to around 15 grams of added kaolin. If you want to get a bit more precise then record the specific gravity of the glaze slop prior to adding kaolin so you can replicate your tests with the entire bucket more accurately.

 

3 - earthenware fired to stoneware temps isn't going to work. Bloating, slumping, brittle clay.

 

I would just dip a couple test tiles for now and include them in your next earthenware firing, maybe they are for that temp. Might be worth further testing, might not.

 

Couple other things come to mind, matt blue turquoise glazes from England immediately bring to mind barium glazes, Different thoughts re barium over on this side of the pond, it isn't used much due to toxicity concerns. Would have to fire it to get a better guess if it contains barium, just be really careful with glaze dust with that one until you have a better idea.. Other thing is since you don't know what is in either glaze the black one could be unsafe for food items also. Might consider using them for non food contact surfaces or decorative use only if you do land up using them.

 

Best thing to do might have been to leave them where they were and not bring them home.



#3 Celia UK

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Posted 21 July 2014 - 10:36 AM

Thank you Min - that's very helpful! I may, or may not decide to 'play around' with theses glazes now. Food safe isn't an issue as I don't make functional pieces, but when I get the chance I can also speak to someone here, to gauge their views too - knowing the likely components in the UK. Think I'll just do some test tiles and make sure they're sitting on a piece of bisque, to protect my kiln shelves, then decide whether to go further!

#4 seancisse

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Posted 21 July 2014 - 03:32 PM

For a) I confirm what said Min: stoneware glaze fire in eathware = it's sallow. No interest.



#5 oldlady

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Posted 22 July 2014 - 05:17 PM

if this works out like the usual Murphy's law, you will have a great glaze that you want to duplicate and use all your life and will not know anything about it.   :)


"putting you down does not raise me up."

#6 Celia UK

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Posted 22 July 2014 - 05:43 PM

Yep! That thought had crossed my mind Old Lady - In which case I might have to use social networking to contact the potter I bought it from, now in the Philippines!

#7 Celia UK

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Posted 30 July 2014 - 03:23 AM

if this works out like the usual Murphy's law, you will have a great glaze that you want to duplicate and use all your life and will not know anything about it.   :)

How right you were Old Lady - I managed to contact the girl who sold me the glaze, in the Philippines who told me it was indeed earthenware glaze - yay! See picture below of a test piece I just dunked in the turquoise matt and fired! I love it - can't wait to try it in a more purposeful way. I have asked if the recipe is her secret, or available to be shared. Let's see what she replies.Attached File  image.jpg   6.04KB   3 downloads

#8 Chilly

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Posted 04 August 2014 - 11:24 AM

if this works out like the usual Murphy's law, you will have a great glaze that you want to duplicate and use all your life and will not know anything about it.   :)

 

+1


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#9 oldlady

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Posted 04 August 2014 - 01:41 PM

i have  just put a glaze on the exterior of a bowl or two. i was given that bucket, 5 gallons is the size people call it, full of something i do not know a thing about except that it is a cone 6 glaze.  it is called Strontium Bronze and i had used it on a planter for my neighbor.  not remembering exactly how it looked except that it is surprisingly beautiful, i drove to my neighbor's house just now and asked to see it again.  she picked up a pot with something growing in it.  the exterior was not something i had ever seen.  she said, "Oh, i changed it by rubbing some bronze paint into it." :unsure:

 

i will have a sample when i get this load fired.


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#10 dhPotter

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Posted 12 August 2014 - 05:04 PM

OldLady,

 

The Strontium Bronze is on p.107 of "Glazes: Materials, Recipes and Techniques" a handbook from CM.  It is called Pinnell Strontium Matt Glaze.

 

My test tiles did not come out like the pics in the book, but that is OK because I like the results it produced.  The pic on the left is the White Glaze, same page number, and the Strontium Bronze by themselves.  The pic on the right is of them layered.  On the left is Strontium Bronze over White Glaze, on the right is White Glaze over Strontium Bronze.  My favorite is White Glaze over Strontium Bronze, it reminds me of a patina sculptural piece in someone's yard.  In the White Glaze it called for Feldspar so I used Custer.  The tiles were dipped quick, 1 second, then half way dipped for 2 seconds then the left top corner dipped for 2 seconds.  This dipping method is described by John Britt in his Glaze DVD.

 

Attached File  IMG_0238.JPG   32.53KB   0 downloads Attached File  IMG_0239.JPG   37.49KB   0 downloads






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