Monday, April 20, 2009

Earthenware Glaze Tests and Recipes

I have just unloaded my electric kiln which had a smallish load of glazed earthenware pots. The firing was to cone 03 well down, possibly nearer cone 02 (about 1100 degrees centigrade).

Pots made by children and adults on the demonstration day.

Most of the reason for the firing was to glaze fire 12 small pots that people made at my demonstration day at Waitati three weekends ago.

I was quite pleased, and relieved, with how they turned out.

I glazed the 12 small pots with a glaze that I have slightly modified from a recipe by Janet DeBoos.

One of my little bowls

At cone 03-02 it will give an aqua green with a nice iron red break in oxidation over terracotta clay,

Wood fired terracotta planter with copper red version of this glaze.

and a good copper red in reduction. It also fits reasonably well, but not perfectly.

Glaze number 17 in More Glazes For Australian Potters by Janet DeBoos is for cone 05-03
Fritt 4124 80
Petalite 15
Bentonite 5
Copper carbonate 6

I have changed it slightly as follows
Fritt 4124 80
Petalite 15
Bentonite 5
China Clay 5
Tin Oxide 1.5
copper carbonate 2

This raises the maturing temperature and the amounts of tin and copper make it suitable for copper reds.

Using Petalite introduces lithium carbonate, and I suspect helps give the alkaline blue-green colour to the glaze.

An 8 1/4 inch bowl by me with the modified DeBoos glaze. Note the feathering of the edges of the cobalt decoration where there was some movement.

I line tested my DeBoos modified glaze base, minus the tin and copper, with other metal oxides added.

The base had a curious response to iron, remaining resolutely honey coloured up to 12 to 16 % iron.

I tested a couple of small pots with the base plus 8% iron, and got quite a toothsome looking rustic glaze, that I mistook at first for one of my lead bi-silicate honey glazes.

I also fired some test tiles and other glaze testers.

Lead bi-silicate= 60, Potash Feldspar= 10, whiting= 5, China Clay= 15, Silica= 10, plus Red Iron Oxide= 2.5. (I think this is an Emanuel Cooper Glaze, or is from one of his books). This gives a satin honey coloured glaze, that is crazing and slightly sugary. All metal oxides are dark and dull over it. I wonder if it needs more heat to improve clarity and fit?

Lead bi-silicate= 100, Red Clay= 22, China Clay= 10, Tin Oxide= 12, gives a silky semi-gloss ivory white with attractive pink where thin over terracotta. Red brown response to iron, and manganese, copper, and cobalt all slightly and pleasantly quietened. Glaze a good fit so far.

Frit 4124= 90, China clay= 10, bentonite= 3, tin oxide= 7, and have a satin to full gloss white that is pale pink over terracotta, and over the white slip on the tile. Iron is straw coloured over it, manganese dull greyish brown, copper good, and cobalt slightly restrained. The glaze is fitting well 4 hours after firing.

Frit 4110= 90, China Clay= 10, plus zirconium silicate= 12, gives a translucent white over terracotta, and a good white over white slip. The glaze has a green response to iron, plummy response to manganese, blue-green response to copper, and cobalt is strong and rich like stained glass. The glaze is a poor fit, crazing as soon as out of the kiln, but would stain as an attractive crackle.

Lead bi-silicate= 80, Red Clay= 20, Tin Oxide= 7, Copper carbonate= 2. This needs to be moderately thick to cover well at this temperature. An attractive creamy green gloss glaze, with red break where thin over terracotta clay. Good fit so far.

This is a little test pot with the lead/tin white glaze that is the same as the second test tile, the floral decoration was to test the oxide response. Manganese around the rim, small brown "flowers" are red iron oxide, green is copper carbonate, and blue is cobalt carbonate.


Barbara said...

Hi Peter, What a lot of work in those glaze tests. love the creamy green over terracotta and the red color on the wood fired planter is so rich.

Arkansas Patti said...

I agree with Barbara. What a lot of work but I know it is a work of love. How wonderful to create.
Really like your finished works but now realize why I am an appreciator of pottery rather than a creator. I have an up coming post showing some of the local potter's works at a festival.
Again, I have alays appreciated the beauty, never understanding the work involve.
Love the pictures on your side bar.

Judy Shreve said...

Your earthenware tests look great. That's a such a nice blue and I really like the iron with the base recipe. It looks like old English slipware.

I'm mixing glazes today. If anything works great I'll let you know. (It'll be a week or so before the glaze firing.)

Peter said...

Hi Barbara, lovely to hear from you, welcome to my site. I had a nice visit to yours when I found your comment here. You have a great vegetable garden by the looks of things. The copper red planter was fired in my wood fired updraft kiln. It is exciting to fire and can give good flame flashing effects on unglazed work.

Hi Patti, thanks for that. In spite of many ups and downs, I do love potting, when I really think about it. It is truly special to take a lump of clay and form something out of it. I look forward to seeing your post with local potters at the festival. It is wonderful to see what is going on all around the world like this.

Hi Judy,
I agree about the glaze with the iron in it looking like English slipware. It gave me a surprise when I unpacked the kiln. It is strange just how much iron that glaze will take without becoming dark brown. I gave up at 16 percent with it still a honey colour! I'd be interested to see how the glaze would work out for you. It is rather nice with chrome, and 2 - 4 percent chromium oxide will give a green with a red break where thin.

Amy said...

wow... what a gorgeous blue shown on the bowls and more! I really like the blue bowl- the closeup of it. great to have discovered your blog. will add it to my blog roll.

Linda Starr said...

What wonderful results and such variations in the glazes for oxidation firing. I love all of the honey colors - do some have black speckles? Your red planter is a wonderful - almost ruby or wine red. Really like the green breaking to red on the terracotta too. Great work Peter and a whole lot of work for you I bet.

Amy said...

Hi...I thought I put a comment here earlier,but I guess not. Glad to have discovered your blog. I really like the rich shades of blue in your bowl pictures. I'll add you to my blog list.

Peter said...

Hi Amy, Welcome to my blog, really nice to hear from you. Copper blues are an interesting addition to the ones that come from cobalt, and this one is useful too, because the glaze fits quite well. Thanks for adding me to your blog list, that is much appreciated, I've put you on mine too.
Sorry you had a problem leaving a comment on the blog. I have that system where I get to see the comments before they appear on the site, which is why they don't appear straight away when you press "Post Comment".

Hi Linda, hope you are feeling better. The honey coloured version of the copper blue glaze does seem to have the odd dark speck in it, and does really come to life when over a white slip on terracotta, especially where the slip is uneven. Early days with the honey variation, but I will play further with it on something bigger, and I should try it over slips with some coarse iron in them, or maybe crushed fired red clay. The red is quite a plummy one and can vary through gray to transparent where hot or thin. Had some trouble with it if hit hard by flame, as it can blister, but is lovely when just right.

Linda Starr said...

Hi Peter, I am feeling slightly better, it comes and goes, I came across this wonderful and interesting pot, Michael Kline posted on his blog, from the Native American museum I thought you might like to see:

Anonymous said...

Sorry Dad, Google experienced some sort of hiccup when I was posting your comment to my site and swallowed it, but I did manage to restore it from my mail box, so it follows below. P.

Dad said

You and CATS Peter! What lovely photos though... almost strokeable... then... some milk??? Yield NOT to alluring felines!
There was an article about Quinces in our local paper the other day. They recommend cooking them at 120C for 6 hours, or overnight... Temperature's somewhat on the low side for you potters, else you might try some in the kiln...
Seriously though, YES Patti, You're right. Peter IS turning out some lovely pottery. It's one of the drawbacks to visiting the OPO... we fall in love with another one (or more!) ... rather like Peter falls for cats,... We really enjoy the ones we've bought already!

Peter said...

Thanks Linda for the link to the pot on Michael Kline's blog, it is wonderful and full of character, and a nice extension of what can be done with a jug. I guess it is all slip decoration and it is instructive, inspirational, and humbling to see how much can be achieved with simple materials. Lovely to hear from you. P.

Thanks Dad for the comment too. Actually I could maintain around 100 - 200 degrees in my electric kiln for an awfully long time, as it takes for ever to cool down at those low temperatures. Maybe I should use it for cooking after all! P.

Unknown said...

Hi, i have seen your work that is remarkable and i would like to requets you to please help me for making transparent glaze receipe, i am doing some tile and pottery work in Karachi (Pakistan)

Peter said...

Hi Azam, thank you for you interest. I would be very happy to help if I can.
Please could you let me know what sort of clay you use, the temperature you fire to, and the sort of kiln you use? Is the glaze intended to cover slip decoration?

Looking forward to hearing from you, Peter

ang design said...

hey peter, great post I'm inspired the copper blue form janet deboos recipe is yum..
I was actually looking for info on chun type glazes and your page came up, I saw a piece by Maud O'Rielly at the Qld art gallery which they termed earthenware - deep plum chun type glaze, the only chun glazes i've ever done are cone 10 which as i'm looking at conserving fuel these days bringing glaze temps down seems to be the way to go.. Is your little wood fired kiln the image on the right side, we're testing a little wood fired raku kiln next month and i think we should be able to get it to 1100deg, i'll post the results..

Peter said...

Hi Ang, welcome to my site! The copper blue does seem to work really well, quite a relief as I have had a lot of trouble with earthenware glazes. I do like the response to copper particularly with that glaze, but other oxides seem to do well too. I even like the chrome greens with this glaze base, it actually manages to look like a glaze rather than green paint! The kiln on the right is my wood fired kiln that I use for most things. I did do a post about my kilns in March (March 21), you might like to have a look at it as the first one that I built and also the seventh one were really raku type kilns. The first hit 1100 degrees in about 2.5 hours with no problems at all.
Good luck with your test firing (always fun!), I'll pop over to your site and check out the results. All the Best, Peter

Caitlin said...

Hi Peter,
I stumbled across your blog looking for earthernware glaze recipies, love your work!
I really love the turquoise glaze and the top cobalt glaze in your line test, there's a lot of work in there.
Do you mind clarifying what oxides you added to the turquoise line test, and also the above cobalt line test?
I live in the Coromandel and make a small range of colourful tiles. I am working on a new range at the moment and that is just the blue I have in my head.
I have a piece of a broken turquoise tile that was found by my cousin on a beach off the coast of south America and I've always loved the vibrancy of it. The blue you created is just like it.
Look forward to hearing back from you!

Peter said...

Hi Caitlin,
Welcome to my site, it is always nice to hear of someone potting in New Zealand..., sometimes I fear that we are an endangered species!

Regarding the glaze on the line test, to be honest, I am a bit confused myself, and I can see why you have asked for clarification!

From what I can remember, and from looking at the sample...I used my modified DeBoos glaze as a base, minus the tin oxide and the copper content. On the turquoise line that you ask about I added 8 percent zircon as an opacifier. So for that the base was as follows:

Fritt 4124 80
Petalite 15
Bentonite 5
China Clay 5
+ zirconium silicate 8

The turquoise line test is copper carbonate added to the base glaze in increments of 1 percent (so you are looking at 0,1,2,3,4 in the photo.

The cobalt line test is similar, but this time there is no zirconium added to the base. I used cobalt carbonate added to the base in increments of 1 percent.

For me, one of the most astonishing things about this glaze base was for it to be able to take up huge quantities of iron oxide with little change of colour. The sample shown above the turquoise line is 0,4,8,12,16 percent red iron oxide and it only achieves a raw sienna colour (I don't think there was zircon in that line).

The glaze samples were fired to between cone 03 and cone 02. I think the glaze would work between cone 03 and maybe as high as 01.

The modified DeBoos glaze with its tin oxide and copper carbonate will also make an interesting red in reduction as shown in the photograph of the wood fired terracotta planter.

Fritt 4124 80
Petalite 15
Bentonite 5
China Clay 5
Tin Oxide 1.5
copper carbonate 2

Hope that answers your question. Do keep in touch and let me know how you get on. You should do some line tests of your own on whatever clay you are using up there.

Best Wishes, P.

Caitlin said...

Hi Peter,
Thank's so much, I can't wait to experiment with those colours!
Yeah it's always so great to hear about what other people are up to, there sure are some pretty clever people out there :)
I would like to send you some of the tiles I make as a thank-you, what would be the best way to get them to you?
I will keep you posted about how I go with the glaze tests.
Thank's again Peter!

Peter said...

Hi Caitlin,
That is really kind of you! You don't needn't send me anything at all, but it would be a big thrill for me to receive a tile never-the-less!

Now for an address hunt!

If you have a look at the links on the right side of my blog, you should find one to Waikouaiti Old Post Office Gallery (under the heading "Links to the Rest of Our Site"). Follow that link. I have a poster of one of my brown crystalline pots on that site at the moment, and around it are our studio hours and some contact details. You'll find our address there. Just add "Otago 9510" after the Waikouaiti part of the address, and it should get to us OK.

If you are confused by all of that..., just send me an Email at opogallery AT gmail DOT com and I will send you our address. Sorry for the "cloak and dagger stuff" I'm trying to avoid having the address hoovered up by some of the Spam bots that like to gobble up such things! Apparently they can read text like this, but can't read photos, bless them!

Best Wishes, and good luck with the glaze. I hope it works out well for you.


Caitlin said...

Sorry for all the messages Peter!
Just found that the other one did come up, Just ignore or delete all the extra messages?!
Thank's for the info regarding your address, i'll follow it up. I totally understand not wanted to put your address up. Am doing a firing this week so will get some tiles off to you!

Peter said...

Hi Caitlin,
Sorry you had difficulties with the message system. My fault really. What I do is allow unmoderated comments for the first few days of a new post, then the system rolls over to a moderated one. This helps me keep track of comments on old posts, but it does make it seem like your comments have been swallowed up by cyberspace! In theory there should be something that pops up for you to say that comment moderation has been enabled and your comment will appear after approval, but I think that may appear at the top of the comments list, and you may not see it?? Anyway, thanks for persisting, and good luck with your firing, I'm looking forward to seeing the results.

Best Wishes, P

Rakesh Soni said...

Hi Peter

wonder ful work. Lot of things to learn as well.I'm a mechanical engineer by profession and discoverd my passion for sculptures recently.
I write a blog on same

I was trying terracota medium. Even After lot of research I could not find the kind of coloured slips to use over red terracotta body, which are devoid of lead etc. I'm not looking to get shades between white-red-brown.
I'm sure you can help.

If you can send me your mail address..I can send you the picture of my sculpture.

Peter said...

Hi Rakesh,

Nice to hear from you, welcome to my site.

I think that it is easiest to apply slip to clay quite soon after the object has been made, when the clay is soft-leather hard. At this point many potters simply make a slip from ball clay, and it will join to the clay quite successfully.

I like to make a slip from 90 percent ball clay, and add 10 percent frit to this. Probably a great many frits would work equally well, but I use Frit 4124 which is a leadless high calcium borosilicate frit (and is the same as Ferro 3124).

This slip will give you a nice cream colour where it is thick over terracotta clay, and will show some of the red colour of the clay through it when it is put on thinly.

To this slip you can add, tin or zirconium to make it opaque white, cobalt carbonate for blue, copper carbonate or chromium oxide for green,
or manganese to make it brown.

You can add even more frit to the ball clay, and make something that is between a slip and a glaze.

On its own, slip decoration will give quite a dry matte finish to the sculpture. If you want it to be shiny, then you can add a clear glaze over the slip.

You are welcome to contact me at
opogallery AT gmail DOT com (make the appropriate changes to the "AT" and the "DOT").

Best Wishes,


Unknown said...

can any one help me with the meaning
of Frit 4124 80

Is the 80 Stands for MESH or the total name(Frit 4124 80)

I am new to ceramic industry.trying to make a mark in it

any reply's would be appreciated

Thanks in advance

Peter said...

Hi Prabu,
80 is the quantity of fritt to use in the recipe. 4124 is a medium soft borax fritt.
Hope that helps, P


Hi Peter, would please be able to guide on the basic components which goes in white slip for terrakotta. Thanks

Peter said...

Hi Tejashree,
White slip for terracotta clay can be made from ball clay, or a mixture of ball clay and china clay this is mixed like a glaze with water, left to stand for a few hours, then sieved to remove any lumps. You will want the slip to be a bit thicker than a regular glaze, rather like cream in consistency. It is best applied when the terracotta clay is leather hard. If the clay is too dry then the slip might not adhere properly. A 50/50 mix of ball clay and china clay is a good place to start. Slip can be applied by pouring, dipping, or brushing it on. I slip the inside of a pot or bowl first, then wait for a few hours for the clay to get leather hard again before slipping the outside.
Hope that helps!