Color of fired clay body

[Kyla]

What factors affect the color that bare stoneware turns in an electric kiln?

I just began firing my own kiln after firing at a shared studio for years. I’m using the same glazes, same buff stoneware, and firing to the same temperature. I wax resist parts of my pottery to contrast with the glaze. At the shared studio, I used to get a lovely toasty orange color on these bare parts, but now it’s all dull beige. 
Is it temperature? Oxygen levels? I’m using a different wax resist but it doesn’t seem like that should make a difference  

Thanks for any help! 

[Min]

Hi Kyla and welcome to the forum.

Both your kiln and the shared studio kilns fired to the same cone? Vented? Could you post a picture of the differences?

[Kyla]

Hi Min- thank you!

Both are vented & same cone. The shared kilns were newer and digital, mine is older and manual… so I’m trying to figure out what I need to do differently to get the same results. 
 

I attached photos. Not shown, but I have tried the exact same glazes in both.  

[Min]

Glazes in your second photo don't appear as melted as in the first photo. I would verify firings with actual cones, did the group studio use cones or did they just go by the temperature? I would think the flashing you are getting in the first photo, and a tiny bit of in the second, is from a fairly high amount of one of the alkali metal fluxes in the glaze (sodium most likely).

[neilestrick]

The toasty flashing around the bare areas is coming from the glaze, either from soluble materials migrating out into the clay as the glaze dries, or from fuming during the firing. Some glazes will have more of that than others. If there's a difference with the same glaze, then it's likely a firing temperature difference, or possibly a difference in drying time if it's coming from soluble materials.

[Babs]

If cant get that flashing at home, you could apply a soda wasb to inglazed areas

[Kyla]

On 5/5/2022 at 2:13 PM, neilestrick said:

The toasty flashing around the bare areas is coming from the glaze, either from soluble materials migrating out into the clay as the glaze dries, or from fuming during the firing. Some glazes will have more of that than others. If there's a difference with the same glaze, then it's likely a firing temperature difference, or possibly a difference in drying time if it's coming from soluble materials.

Thanks for the insight Neil. I have been seeing the difference even with the same glazes. At the shared studio, I would get the flashing consistently with multiple glazes at both cone 6 and cone 10, and now I'm not. 

If it's a matter of the glaze traveling into the clay... would bisque firing to a lower temperature make the glaze absorb/migrate more? I've been going to 04 for the bisque, I'm not sure what the shared studio was firing to. 

[Babs]

Does the studio fire a gas kiln or electric?

[Callie Beller Diesel]

On 5/6/2022 at 8:57 PM, Kyla said:

would bisque firing to a lower temperature make the glaze absorb/migrate more? I

That depends on your clay body. They can vary.

To verify if it makes a difference or not, make 2 test bars of clay and fire them to the 2 different bisque temperatures, verifying with cones. You can do an absorbency test As described here to see what it does.