Kaolin & Flashing Slips

As part of the MN NICE program, I did research investigating flashing slips.  I wanted to test the effects different kaolins had on the slip.  Here are the results of my tests.  Most of these recipes follow the "basic slip recipe" found in Gail Nichols' book Soda, Clay and Fire (80% clay, 10% silica, 10% neph sye).  All of these tests were done using B-Clay (left) and Soda Clay (right), both from Continental Clay.  These tests were all done in cone 10 reduction soda firings.  

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Calcined EPK

80% - Calcined EPK

10% - Silica

10% - Neph Sye

+5% - Bentonite 

 

This slip has a lovely matte finish and a nice textured feel.  I think it contrasts the darker clay body nicely.  This slip works best when applied to bisque ware - I had a lot of cracking and flaking when I applied it to leather hard work.  Brushing this slip onto a piece also provides a nice range of color.  

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Minnesota Kaolin

80% - Minnesota Kaolin

10% - Silica

10% - Neph Sye

+5% - Bentonite

 

I was fortunate enough to get a hold of a sample of kaolin mined in Minnesota from a local mining company.  When fired, it has a dark brown color with a lot of interesting speckling.  I suspect this is due to the coarseness of the raw material I received.  I am curious to try ball milling a small amount to see how it changes.  This slip works well when applied to both leather-hard work (above) and on bisqueware (below).  

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50/50

40% - Calcined EPK

40% - Minnesota Kaolin

10% - Silica 

10% - Neph Sye

+5% - Bentonite

 

This slip is a mixture of the above two kaolins.  It works well when applied to bisqueware (I haven't had a chance to test it on leather-hard work yet).  I am curious to continue modifying the ratio of the kaolins.  

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EPK

80% - EPK

10% - Silica

10% - Neph Sye

+5% - Bentonite

 

This slip produces a dull orange color.  It works well when applied to both bisqueware and leather-hard work.  I may try mixing this slip a bit thicker and trying this test again.  

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Grolleg

80% - Golleg

10% - Neph Sye

10% - Silica

+5% - Bentonite

 

This slip stayed pretty white, though there are subtle blushes of color here and there.  It works well on both leather-hard work (above) and on bisqueware (below), though there was some slight cracking on the Soda clay (right).  

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Helmer Kaolin

80% - Helmer Kaolin

10% - Neph Sye

10% - Silica

+5% - Bentonite

 

This slip produced some nice oranges and yellows.  It works only when applied to leather-hard work.  I had a lot of issues with cracking on bisqueware.  

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Ben's Avery slip

32% - Grolleg

20% - Calcined EPK

40% - Neph Sye

8% - Redart

 

I found this slip recipe online.  It originally called for Newman Red clay but I did not have any, so I substituted Redart instead.  There was some subtle cracking when applied to bisqueware (pictured).  I will have photos of this slip applied to leather-hard work after my next firing.  

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Johnston Flashing Slip

50% - Grolleg

30% - Neph Sye

10% - EPK

10% - Redart 

+3% - Bentonite 

 

This is another recipe I found online.  This one also called for Newman Red, so I had to substitute it for Redart.  It had some slight cracking when applied to bisqueware (above) and was completely smooth on leather-hard work (below).