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glaze help!


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#1 etched

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Posted 19 January 2013 - 12:13 AM

Hi Everyone!

I'm very new here and really happy to have found this forum. I have read other posts on pin holing issues with glazes and I am having the same issue, but i cant work out if they are really pin holes or not. Some of them kind of seem like creators and are smooth indentations on the glaze while others are small sharp bumps.

Here is what I'm using and how:

I'm using is southern ice porcelain clay. I'm firing to 1240 degrees C for my bisque fire. I leave the bungs out till 750 degrees. (I use a small electric kiln)

I use underglazes on the greenware.

I'm using a store bought glaze mix Northcote pottery (here in Australia) They have had a issue of late with a change in formulation due to an ingredient going off shore. This change has caused the glaze to be thicker in consistency and has major issues with it crawling. They have advised to go from 2 coats to 1 careful coat otherwise the glaze crawls, but its far from perfect. If it is slightly thick in a spot it will crawl or cause a frozen ripple effect slight but noticeable. It has also been causing pin holes as shown in the photos. I have been mixing 1:1 northcote pottery stoneware glaze with a cessco stoneware glaze and this has helped with the crawling and rippling and some of the pin holes but has not helped with the pin holes a great deal. This glaze(Northcote pottery)by the way used to be PERFECT and almost fool proof glaze. I'm not just using straight cessco either as the glaze looks less glossy and like there are very slight and very tiny dimples over the surface of the glaze.

Anyway any advice?

I'm self taught but have working with the same materials for 4 years. I need my glaze to be very clear as the designs under the glaze are the feature of my work. I have tried out every other store bought glaze that I could get my hands on in Australia that will fire to 1280 (there are very few) but they don't work as well (or as well as this glaze once worked) or are as clear.

Help!

Lilly

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#2 neilestrick

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Posted 19 January 2013 - 11:02 AM

You said you bisque to 1240C. Any reason you're firing so hot for bisque?
Neil Estrick
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#3 etched

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Posted 19 January 2013 - 06:10 PM

You said you bisque to 1240C. Any reason you're firing so hot for bisque?


sorry that is hot! I meant to say 1040C

#4 Stephen C

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Posted 19 January 2013 - 10:43 PM

So if you can't find it commercially then why not try mixing one yourself. What you could do if you want to give it shot at mixing your own is take a Celedon recipe, such as Pinnell Celadon, and remove the opacifiers and colorants. This glaze is a very nice transparent celadon so altering it to a clear would make a very nice smooth clear.

Pinnell Celadon
Custer Feldspar 24.50g
Silica 34.30g
Whiting 19.60g
Grolleg Kaolin 19.60g
Barium Carb. 1.90g
Tin Ox. 1.00g
Yellow Iron ox. 0.50g

So if you remove the Yellow iron and the Tin from that recipe you should end up with a nice clear. Also Barium can be substituted 1:1 with Strontium Carbonate. This glaze is very stable and doesn't crawl or pinhole. I know in the states this is a very affordable glaze to put together minus the Tin which you wont need anyway.
Hope this was helpful, i dont think i missed anything in terms of the chemistry but mixing up a few test batches 100-200g couldn't hurt.

example clear

Custer Feldspar 24.50g
Silica 34.30g
Whiting 19.60g
Grolleg Kaolin 19.60g
Strontium carb. 1.90g

Total 99.9%

#5 Mark C.

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Posted 20 January 2013 - 03:34 AM

If you are looking for a simple clear glaze at cone cone 10-2250 degrees or cone 11 2259 degrees I can post one -its thin and very clear-I covered cobalt drawings for years and you could see right thru it. It durable and holds up to functional use as well. I can dig it up if you want to try it?
Mark
Heres a few old drawing with it at cone 10 on porcelain in reduction fire.These where made in the 80s with cobalt pencils and wash on brushes-takes a steady hand.
Flying fish covered jar and a dinner plate with gold blue fish

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Mark Cortright
www.liscomhillpottery.com

#6 Chantay

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Posted 20 January 2013 - 03:58 AM

Mark, those are really beautiful. I'm trying to achive a similar look at cone 6. What type of wash did you use? I have been using underglaze but am not really satisfied with the results.

-chantay
- chantay

#7 etched

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Posted 20 January 2013 - 04:11 AM

So if you can't find it commercially then why not try mixing one yourself. What you could do if you want to give it shot at mixing your own is take a Celedon recipe, such as Pinnell Celadon, and remove the opacifiers and colorants. This glaze is a very nice transparent celadon so altering it to a clear would make a very nice smooth clear.

Pinnell Celadon
Custer Feldspar 24.50g
Silica 34.30g
Whiting 19.60g
Grolleg Kaolin 19.60g
Barium Carb. 1.90g
Tin Ox. 1.00g
Yellow Iron ox. 0.50g

So if you remove the Yellow iron and the Tin from that recipe you should end up with a nice clear. Also Barium can be substituted 1:1 with Strontium Carbonate. This glaze is very stable and doesn't crawl or pinhole. I know in the states this is a very affordable glaze to put together minus the Tin which you wont need anyway.
Hope this was helpful, i dont think i missed anything in terms of the chemistry but mixing up a few test batches 100-200g couldn't hurt.

example clear

Custer Feldspar 24.50g
Silica 34.30g
Whiting 19.60g
Grolleg Kaolin 19.60g
Strontium carb. 1.90g

Total 99.9%


thanks Stephen, I'm a little nervous making my own glaze but I'm willing to have a go, though I would still love to be able to use my old glaze. I know anything about the raw materials is this recipe a food safe one and is it gloss?

#8 etched

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Posted 20 January 2013 - 04:19 AM

If you are looking for a simple clear glaze at cone cone 10-2250 degrees or cone 11 2259 degrees I can post one -its thin and very clear-I covered cobalt drawings for years and you could see right thru it. It durable and holds up to functional use as well. I can dig it up if you want to try it?
Mark
Heres a few old drawing with it at cone 10 on porcelain in reduction fire.These where made in the 80s with cobalt pencils and wash on brushes-takes a steady hand.
Flying fish covered jar and a dinner plate with gold blue fish

they look amazing Mark! I would love to have the recipe. I'm needing the glaze to be food safe and a gloss glaze, does this fit the bill?
As I said to Stephen I know nothing about mixing glazes and their ingredients. But fear shouldn't be a reason for not learning.

I would really like to know though what you feel could be happening with my current glaze Do you have any thoughts or suggestions?

cheers
Lilly

#9 voceramics

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Posted 20 January 2013 - 07:45 AM

It looks like your pinholes are at the point where they're trying to heal over with glaze. I had this problem with some of the commercial glazes I'm using, slowing down the cooling really seemed to help give the glaze time to lay back down and flow over the bubbles or craters. You can use a program to control the cooling which can get very expensive in terms of electricity, or use extra thick shelves during firing and stack the kiln fairly tight with a shelf capping the top of your kiln load. The thick shelves act as a heat sink and the cap keeps the cooler inlet air from flowing directly over the pieces.

The pinholes happened more with platters and plates for me, rather than bowls or vertical surfaces that allowed glaze to flow more readily.

It's possible what's causing your pinholes is different than what caused mine, so slowing down the cooling may not help with the problem.
Phuong
Vo Studio Ceramics
www.vostudioceramics.etsy.com

#10 Mark C.

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Posted 20 January 2013 - 02:04 PM


If you are looking for a simple clear glaze at cone cone 10-2250 degrees or cone 11 2259 degrees I can post one -its thin and very clear-I covered cobalt drawings for years and you could see right thru it. It durable and holds up to functional use as well. I can dig it up if you want to try it?
Mark
Heres a few old drawing with it at cone 10 on porcelain in reduction fire.These where made in the 80s with cobalt pencils and wash on brushes-takes a steady hand.
Flying fish covered jar and a dinner plate with gold blue fish

they look amazing Mark! I would love to have the recipe. I'm needing the glaze to be food safe and a gloss glaze, does this fit the bill?
As I said to Stephen I know nothing about mixing glazes and their ingredients. But fear shouldn't be a reason for not learning.

I would really like to know though what you feel could be happening with my current glaze Do you have any thoughts or suggestions?

cheers
Lilly


As far a fixing your glaze I would soak it at temp for some time to see if they flatten out next fire. I do not use commercial glazes at all so without knowing what's in the mix its harder to fix. The hold or soak may help. I assume you are firing in oxidation in an electric to cone 10? The hold at temp can make the glaze flow and lay flat- slow cooling will also help. If this is a clay body issue this may make for more bumps-so a test is needed.I think Southern ice is a solid non issue body and can take cone 11/
Now to this clear glaze its a very simple glaze and some materials can be swapped if you have different ones down under.
HT 51 clear cone 10
Custar feldspar (any potash feldspar will work)----- 27
Ball clay we use OM4 but most ball clays will work-19.5
Whiting 19.5
Silica 300 mesh-use fine mesh for better melts 34
total 100
if you are new to glaze making just add a zero to all columns to make 1000 grams etc
All my experience with this glaze (40 years) is with it on porcelain fired in reduction cone 10+ fires
Mix and apply this on the thin side. I have poured this glaze as well as dipped and sprayed it-the key is a uniform thin coat-rub out any lumps or bumps after it dries.
This glaze works best when fired HOT as its more clear-less clear when cold.

Now for the person who asked about the wash used in the drawings-The main work is done with cobalt drawing pencils with some homemade cobalt wash brushed on as in the rim line on the dinner plate.
Add water to small amount of cobalt Carbonate-the more you add the stronger the wash. This wash can be made with most colorants .If you make a mistake it cannot be undone as there is no erasing . I suggest mixing all your colorants and test fire them on some scrap bisque all as washes-you will find many are very good
.There pots where made by me and drawn by an old girlfriend many years ago-we did lots of this back in the day (80s). She is a very good at drawing-She still makes my signs these days as my wife and I are not good at drawing-in fact drawing was my hardest art class when i got my art degree.
Mark
Mark Cortright
www.liscomhillpottery.com

#11 etched

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Posted 23 January 2013 - 06:25 PM

thanks everyone for your help!

I'm trying a few different tests, one with a slower cool down to 1000C one with a higher fire to cone 10 and I will be trying out my own glaze experiments when I can get my hands on the raw materials when I go to the suppliers next week.

fingers crossed.

Lilly




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