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PeterH

Member Since 28 Apr 2013
Offline Last Active Yesterday, 10:40 AM
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Posts I've Made

In Topic: Red Casting Slip

26 July 2014 - 05:25 PM

>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.c...merica_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

 

 


In Topic: Red Casting Slip

26 July 2014 - 06:55 AM

>>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.alf... Procedures.pdf
... which seems to be an extract from a much larger document
http://www.claystore...ip casting).pdf
 


In Topic: Mold Hot Spot

26 July 2014 - 06:33 AM

What is a hot spot? [I assume that you are talking about casting slip in a plaster mould.]

Regards, Peter


In Topic: Amorphous Silica Vs Just "silica" In Glaze?

07 July 2014 - 07:56 AM

You might want to check if your supplier lists flint or quartz. I've never bought

"silica" in the UK other than as flint or quartz.

 

Quoting from Digitalfire http://digitalfire.c.../flint_316.html

The terms flint, quartz and silica have come to be used interchangeably in

ceramics and you will see them all employed in recipes

 

Regards, Peter


In Topic: Getting The Perfect Gloss From Terra Sig.

29 June 2014 - 01:34 PM

Tyler, Try www.bookfinder.com for Fred Matson's Ceramics and Man, they list several copies,