Is there any way to "whiten" red clay?

[Tabathos]

Hi. I'm relatively new on ceramics. Currently doing pieces using red clay. The problem I have is trying to achieve a uniform glaze colour. Since the red clay is the base, it passes through the color of the commercial glazes (I'm using Duncan cone 06). My teacher told me to add a caolin layer before applying the glaze,  but the results are far from satisfactory. Some parts exploded, other parts have a depressing yellowish tone, really dreary to see. 

You may think that why not using white clay. It is kinda expensive and it's not as moldable as the red one. Also it is difficult to find in my country. The red is perfect except for this issue.  I've emailed the manufacturer, and they told me to use white bisque (hahaha), or to use opaque glaze. It would be nice if I haven't spent a lot of money on semi-transparent glazes and some underglazes

Any recommended input? I've been told to layer caolin over the greenware before bisque, or to use a white engobe over the greenware, but I'm not sure what to do.  

[liambesaw]

Try using a white slip, fishsauce slip is a good recipe for many bodies, add some zircopax to really kick up the whiteness.

[oldlady]

welcome to the forums, tabathos.   what country?  does your clay have a cone number that it is fired to?  is it terracotta clay"?   there are many other bits of information that would help someone who is familiar with your problem make a good suggestion.  what suppliers are available to you?

(Kaolin is a type of clay.)

[Tabathos]

6 minutes ago, liambesaw said:

Try using a white slip, fishsauce slip is a good recipe for many bodies, add some zircopax to really kick up the whiteness.

Found this recipe: 

Fish Sauce ^04-^10
Minspar 23.50
Grolleg Kaolin 43.60
Pyrophyllite 7.80
Bentonite 9.50 (or substitute 6.3 macaloid if your bentonite has specks)
Silica 15.60
100.00

What proportion of zircopax do you propose?

[Tabathos]

4 minutes ago, oldlady said:

welcome to the forums, tabathos.   what country?  does your clay have a cone number that it is fired to?  is it terracotta clay"?   there are many other bits of information that would help someone who is familiar with your problem make a good suggestion.  what suppliers are available to you?

(Kaolin is a type of clay.)

Thank you very much. I'm from Costa Rica. It is fired on cone 04. I'm not sure if it is terracotta, there's attached a picture of a bisque as reference. 

Regarding suppliers, I know that this red clay is widely available. The white one we use is imported from Mexico, but I've tried it and it's like using polymeric clay.

I'm thinking on mixing kaolin with the red clay, but I'm unsure if it is safe to use. 

[Callie Beller Diesel]

If you mix the red and white clays together, it will not stop the iron in the red clay from coming through your glazes. If you mix kaolin to your red clay it won’t do anything to the colour.

As a fellow red clay user, your best options are indeed to either add a layer of white slip/engobe, or to embrace the way the colour of the clay comes through the glazes. It can create some beautiful effects.

You describe pieces popping off when you applied kaolin slip to your piece, and that the places where it stayed it was yellowish. Did you apply the slip to bisque and then glaze over top, or did you apply the slip to the piece while it was leather hard? With many slip recipes, or even just straight kaolin, when you apply it will affect how well it sticks to the piece. Leather hard is the best stage usually. 

The yellowish colour of the slip after firing could be that the layer of slip was too thin and the iron from the red clay was coming through that too. It could be a kaolin that naturally contains things like iron or titanium that will make things less white. Do you know what kind of kaolin it is? What does it say on the bag it comes in?