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Hi, I have recently been experimenting with converting a few of my production pieces to slip cast pieces. I took a Hiroe Hanazono workshop at Arrowmont, ( excellent BTW ) and learned the basics of slip casting. Since then I've made molds of my pieces and have cast several of them. Everything is going swimmingly except...

My work is all in a red clay, I use RedRock from Highwater, fire it to a hot 5 / cool 6, I have made a slip from RedRock by drying then adding 40% water and .3% Darvan 811. The problem that I'm getting is that my slip keeps gelling up. I've already got over the maximum amount of deflocculant in it, and have had to add water anyway bringing my specific gravity down to 1.6 instead of the desired 1.75. It's working, but still gelling, I assume from the Iron in the clay. Does anyone have a good cone5/6 red slip for slip casting recipe? I don't mind if it is speckled or not, and it doesn't have to match red rock exactly, just be red.

 

I appreciate any input !

Thanks

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I don't have an answer to your question, but the fact that your clay is reacting differently than what you used at the workshop is not surprising. The formula for casting slip will vary for each clay body, depending on its clay content, etc. The 40% water and .3% Darvan is just a starting point.

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You could also use a white clay body that you add colorant to before pouring.

I'm thinking this may be the way to go, It's probably the iron that is making it gel up so much, so if I add a mason stain, it may be the best way to go.

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>>You could also use a white clay body that you add colorant to before pouring.

>I'm thinking this may be the way to go, It's probably the iron that is making it gel up so much, so if I add a mason stain, it may be the best way to go.

 

I'm sorry your query hasn't attracted more attention.

 

I don't have a lot of experience making casting slips, but the only time I've tried to make
a casting slip from a red clay it was an entirely painless and successful exercise. It was
a UK terracotta clay, and the iron content wasn't an issue. To be sure the supplier listed
it as suitable for making casting slip, and supplied a body-specific recipe.

Here are two ideas for you to consider (I don't think my level of experience allows me to
recommend any course of action).

1) Follow the advice of the highly knowlegable Neil Estrick. Have another try with your
   existing body, judging the level of deflocculant by the effect on the slip rather than
   applying some context-free upper limit.

2) Look to see if your supplier lists any red clays as suitable for casting slips, if you're
   lucky they may even suggest a recipe. Look at powdered clays as well as moist ones.

Regards, Peter

FYI I pass on an Alfred guide on making casting slip in case it is of any help to you in
judging the amount of deflocculant to use. You will have to judge its utility yourself, I
certainly haven't tried it. [Now I just tweak a UK porcelain casting slip pre-mix.]

http://claystore.alfred.edu/rawmats/resources/Dispersant%20Addition%20Procedures.pdf
... which seems to be an extract from a much larger document
http://www.claystore.alfred.edu/rawmats/presentations/Raw%20Mats/Class-10%20%28slip%20casting%29.pdf
 

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>>You could also use a white clay body that you add colorant to before pouring.

>I'm thinking this may be the way to go, It's probably the iron that is making it gel up so much, so if I add a mason stain, it may be the best way to go.

 

I'm sorry your query hasn't attracted more attention.

 

I don't have a lot of experience making casting slips, but the only time I've tried to make

a casting slip from a red clay it was an entirely painless and successful exercise. It was

a UK terracotta clay, and the iron content wasn't an issue. To be sure the supplier listed

it as suitable for making casting slip, and supplied a body-specific recipe.

Here are two ideas for you to consider (I don't think my level of experience allows me to

recommend any course of action).

1) Follow the advice of the highly knowlegable Neil Estrick. Have another try with your

   existing body, judging the level of deflocculant by the effect on the slip rather than

   applying some context-free upper limit.

2) Look to see if your supplier lists any red clays as suitable for casting slips, if you're

   lucky they may even suggest a recipe. Look at powdered clays as well as moist ones.

Regards, Peter

FYI I pass on an Alfred guide on making casting slip in case it is of any help to you in

judging the amount of deflocculant to use. You will have to judge its utility yourself, I

certainly haven't tried it. [Now I just tweak a UK porcelain casting slip pre-mix.]http://claystore.alfred.edu/rawmats/resources/Dispersant%20Addition%20Procedures.pdf

... which seems to be an extract from a much larger documenthttp://www.claystore.alfred.edu/rawmats/presentations/Raw%20Mats/Class-10%20(slip%20casting).pdf

 

Hi Peter thanks for the info! My understanding speaking to Hiroe Hanazono is that in terra cottas the iron content doesn't affect the slip, but that in stoneware it can... Go figure?

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>My understanding speaking to Hiroe Hanazono is that in terra cottas the iron content doesn't affect the slip, but that in stoneware it can... Go figure?

... interesting

I found this statement in a Digitalfire article on low-fire terrcotta casting slip

Adding iron oxide to a clay causes it to gel badly on dispersion however the natural form of iron in Redart does not do this at all.

http://digitalfire.com/4sight/education/understanding_the_terra_cotta_slip_casting_recipes_in_north_america_132.html

So perhaps it depends on how the iron gets into the body, in a red clay or as iron oxide. [Hand-waving hypothesis.]

 

Have you tried adding more deflocculant to a small sample of your body? Does it thin it further? How does it modify the gelling issues?

 

Regards, Peter

 

 

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