They're all the same.

I just wanted to post these cups I recently got out of a kiln to show you how difficult glazing is even in the best of times. I glazed these all the same. They are Pinnell Celadon inside on porcelain and then the next day I dipped the bottom in Val's Satin Black about an inch or so . Then I dipped the top in Daly Red, then dipped it in Daly with Titanium and last I dipped the top 1/2" in Val's Satin Black again.

Then I fired them on the same shelf in the same kiln.

They all look fine but some are hotter and more runny, some are a bit underfired and stiffer and some are about right.

No wonder people use Rhodes 32!

Pinnell Blue Celadon cone 10

24.75 Custer Feldspar
34.65  Silica
19.80  Whiting
19.80  Grolleg
 1.98  Barium Carbonate

Add 1.0 Tin Oxide
        0.5 synthetic iron oxide

Val’s Satin Black  cone 10
20.00 g. -Soda Feldspar
20.00 g. –Cornwall Stone
  2.00 g.- Whiting
20.0 g. – Silica
10.00 g –Ball Clay 
13.00 g –Talc
15.00g -  Dolomite

3.00 Red Iron Oxide
2.00 Manganese Dioxide
3.00 Cobalt Oxide
1.00 Chrome Oxide

Daly Red and Daly Red with Titanium cone 10 reduction

35.00 Nepheline Syenite
15.00 Whiting
27.00 Silica
17.00 Frit 3110
  2.00 Zinc Oxide
  1.00 Bone Ash
  3.00 Talc

 0.50 Copper Carbonate
 1.50 Tin Oxide

Add :  
 3.00 Titanium Doixide


Anonymous said…
Why do potters use glazes containing Barium Carbonate? I thought it is unsafe to use , especially inside functional ware e.g cups that people may use for juice, etc.
Can you please give me your opinion on this John.Thank you.
Lori Buff said…
I would love to show this article to people who ask if we've changed the glaze recipes because the pieces look slightly different from one firing to the next. This really shows how they can act differently.
Remind us of how you fired them (ox, reduction...?)
John Britt said…
I fired them in reduction - my R1 cycle.

Barium carbonate is toxic but if it is in a glaze that has enough silica and alumina it won't leach. I have had this glaze tested numerous times for my book and it doesn't leach. It is only 1.9%. Now if you had a glaze with 15% - 50% barium carbonate you would have problems. Or if you added copper carbonate that would exacerbate the leaching.

Almost all ceramic colorants are toxic, cobalt, chrome, manganese, nickel, copper, etc. You don't stop using them do you? No, but you learn what, why and how they are toxic and take proper precautions.

Just my take on it.
Amy Waller said…
Just wanted to say this is awesome. Thanks for sharing those photos.
John Britt said…
Probably a lot like humans, they are all the same except when you have to spend time alone with them in a room.....