Ceramic body stain issues. Cant achieve desired colours with Chromium Tin Pink stains

[Sarcasticcrab]

Hey all,

 

I have been experimenting with different ceramic stains in the bodies of clay but have really struggled to achieve any of the warm colours. I have read that chromium tin stains require a high concentration of calcium so have added CaCO3 to my samples. You can begin to see some of the purples coming through in some of them. Should i go even higher than 12%? I have also read that clay bodies should have low alumina. The clay body i have been using has 24.7% Al2O3, is this too high? Please see the images of my samples and the stain compositions at the link below:

https://imgur.com/a/b6ySVAa

 

 

 

[Sorcery]

I think low magnesium is also important as high calcium.

Sorce

[Min]

Glazes need to have high calcium with the alumina on the low side and preferably lowish magnesium to develop chrome tin reds, pinks and purples. Calcium is used as one of the main fluxes in the glaze. By adding 10-12% calcium carbonate to your body it's going to have an effect on the clay maturity as it's a flux. The body will already (hopefully) have the fluxes it needs to be balanced, adding a significant amount of calcium is going to throw this out of whack. By the very nature of clay it's going to have high alumina, there is no getting around that. There are alumina pink stains (made from alumina and manganese) that are designed as body stains that don't have the same requirements as the chrome tin stains. For reds and purples you might be looking at cadmium inclusion stains to get the colour you need. 

[Sarcasticcrab]

Thank you both, that is very helpful!

17 hours ago, Min said:

Glazes need to have high calcium with the alumina on the low side and preferably lowish magnesium to develop chrome tin reds, pinks and purples. Calcium is used as one of the main fluxes in the glaze. By adding 10-12% calcium carbonate to your body it's going to have an effect on the clay maturity as it's a flux. The body will already (hopefully) have the fluxes it needs to be balanced, adding a significant amount of calcium is going to throw this out of whack. By the very nature of clay it's going to have high alumina, there is no getting around that. There are alumina pink stains (made from alumina and manganese) that are designed as body stains that don't have the same requirements as the chrome tin stains. For reds and purples you might be looking at cadmium inclusion stains to get the colour you need. 

 

Min,

I have found a clay online with 19.2% Al2O3 and 1.8% CaO (The clay i used above is 24.7% Al2O3 and 0.19% CaO). Do you think its worth buying some and giving it a go with the stains I have?

I will also look for cadmium inclusion stains and alumina pink stains, but I live in the UK, where there doesn’t seem to be a huge range of options. (Only limited Mason stains are available)

 

[glazenerd]

Porcelain bodies will have 22-25% alumina, and stoneware lower. Alumina content will effect color development in red bodied clays: but typically only effects lighter pigment stains. . The % of stain required in a clay body will always be higher than glaze: because the molar % is different. Encapsulated stains do not work well in clay bodies because because the amounts of calcium or zinc required to release them is also much higher than glaze. Go through the Mason stain chart and find those specifically marked as "body" stains. The red body stain will produce a bright red at 12%, and lower % will produce pastels. I often mix different % of colors to get teals, etc.

Tom

[Min]

 

5 hours ago, glazenerd said:

Encapsulated stains do not work well in clay bodies because because the amounts of calcium or zinc required to release them is also much higher than glaze.

@Chris Campbell has success with them, she mentions using Tangerine and Lobster which are encasulated cadminum stains.  @Sarcasticcrab, Chris isn't active on this forum anymore but you could try send her a pm asking her advice. She fires cone 10 porcelain with Mason stains. Image below from her website where she lists some of the stains she uses and the percentages. (she uses Mason 6020 for pink which is an alumina/manganese stain)

edit: there should be an informational chart available for the stains you are using listing there composition which you could cross check with the Mason reference chart.

[glazenerd]

Min correction noted. Should have been more clear. I use tangerine, purples, etc. most run in the $25-30 a lb range, and require 8-10% additions to achieve color saturation.