Jump to content
Sign in to follow this  
Rippity

Will the real cone please stand up?

Recommended Posts

Newbie here.  I started in November and have fired my kiln four times (2 bisque, two glaze) with pleasing results. 

I use Amaco Stoneware Clay 38.  Typically I fire it to cone 7 (I was shooting for cone 6, but my kiln fires hot).  Recently I found this info connected to the clay I buy: 

"Bisque fire to Cone 04 (1971°F, 1077°C). The firing range is Cone 5–10 (2205°–2381°F), and the recommended glaze firing is Cone 10 (2381°F). At Cone 5 (2205°F), shrinkage is 13% and absorption is 7%. At Cone 10 (2381°F), shrinkage is 15%, absorption is 1.4%, and the clay fires white in oxidation and gray in reduction, both delicately peppered with darker gray spots."

So my question is this: What does "recommended" mean to the fired pieces I've already made? Should I change my firing range to high, rather than mid level? What about the cone 6 glazes I've been using? If I begin to fire at cone 10, should I still use the Amaco cone 6 glazes?  What does cone 6 vs cone 10 mean in terms of glaze usage? ...and is it even necessary to change courses?

TIA

Share this post


Link to post
Share on other sites

Keep firing to cone 6, but change your clay body. Firing to cone 10 will put unnecessary wear on your kiln and burn out your elements much faster. A lot of clay companies say their clay works from cone 5-10, but it's a lie. I think it's a throwback to to the days when not so many people fired cone 5/6, and they didn't want to make clay bodies just for them. If you fire a cone 10 body to cone 6, it will be underfired, and won't be water tight. Run a mug made o that clay through the dishwasher and the exposed clay at the foot will absorb water and weep it out on your table or in your cabinet. If the glaze is crazed, whatever is in the mug will be absorbed through the glaze cracks and into the wall of the pot. Good luck cleaning that out. So get a clay body that will have less than 2% (1.5% ideally) absorption at cone 6.

Share this post


Link to post
Share on other sites

Okaaaaay. First, thanks for the prompt reply.

Typically I buy from Amazon for the free shipping.  Advice on where to buy said 6 cone clay? I have often used The Ceramic Shop in Philly.  

Another question: Is a 15% shrinkage NORMAL? It seems like A LOT. 

Share this post


Link to post
Share on other sites
4 minutes ago, Rippity said:

Okaaaaay. First, thanks for the prompt reply.

Typically I buy from Amazon for the free shipping.  Advice on where to buy said 6 cone clay? I have often used The Ceramic Shop in Philly.  

Another question: Is a 15% shrinkage NORMAL? It seems like A LOT. 

Buy locally in bulk and 12% shrinkage is fairly standard, 15% is a lot.  But just like absorption testing, you should test your shrinkage when you fire too.  Make a 100 mm slab and let it dry, measure it (wet to bone dry measurement), bisque fire it (dry to bisque fire measurement), then fire it again to cone 6 (final fire measurement).  The difference between wet and cone 6 is the total shrinkage.

Share this post


Link to post
Share on other sites

I fired #38 to what couldn't have been cone 8 and it didn't absorb any water after 24 hours or after the 5 hour boil test. 

I think the #46 was recently reformulated to be less absorbent at cone 5, I tested that vitreous before too. I like that ...

Though I couldn't find it at Walmart anymore.

Use Standard in PA!

 

Sorce

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.