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Slipaholic

Sgrafitto Slip, need help…

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Hi, I would like help in understanding what makes a good slip for sgraffito. I’ve tried quite a few recipes through the years but none has been truly reliable. Usually they either crumble while I’m drawing the design or don’t turn out completely white (showing some red of the clay beneath). I think part of the problem maybe that I apply it to bone dry pots (I’ve tried sponging water before applying the slip), single fire and I would like to keep it that way. I have some glazes mostly just Gerstley Borate with some additions that work well, but none are white and I’m looking for a reliable white background. I fire cone 04-03 electric. The work isn’t utilitarian, so I’m not too concerned with the glaze on top crazing…

 

Any ideas on how I might work out a solution?

 

 

Thanks,

 

Slipaholic

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Ya this is an application issue. You should try using a good engobe recipe and applying it while the pot is as wet as you can get away with. This will help adhesion. I often apply a deflocculated engobe when the pot is leather hard just after trimming and then cover it in a bucket to allow the pot and engobe to come back to leather hard as a cohesive whole. Then do the carving when the pot is a good leather hard so you get crisp lines and clean cuts. I try and apply the engobe quite thin, the thinnest layer possible actually.

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There are a few recipes in a good book I have from Richard Zakin called Electric Kiln Ceramics.

 

This one might help with your iron burn through slightly because it contains a zirconium opacifier.

 

Six Corners Engobe I, cone 04

Boron Frit - 48

Soda Spar - 12

Ball Clay - 30

Zirconium Opacifier - 8

Tin - 2

 

This one is listed as being dry surfaced and very durable

 

Fair Haven Engobe, cone 04

Boron Frit - 23

Soda Spar - 42

Ball Clay - 33

titanium - 02

 

 

You might give these a test and see if they work for your process. I've found most things in this book just work. For Boron Frit it's calling for 3124 in most recipes. OM-4 ball clay. I think the last time I went they sold me uni-spar for a soda spar, but anything that will mimic Kona f-4.

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Thanks… I have Zakin’s book here, I’ll check it out.

 

Is there a particular reason for choosing an engobe for leather hard pots?

 

The thing though, is that I rather change slip/glazes than the way I work. I usually don’t clean or work pots until they are bone dry. Since commercial underglazes and GB glazes have worked, I thought maybe someone here might have been able to tell me the elements I need to take into account in formulating a slip that would fit (no pun intended) my current way of working.

 

Regards,

 

Slipaholic

 

 

 

 

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I don't even like touching my pots when they are bone dry personally. I have more casualties from breakage at that stage than any other. I think that's why most recipes I see are for leather hard. Good luck with your pots.

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The problem with working bone dry is that slip just won't adhere properly. Slip is, after all, just a wetter form of moist clay, and therefore must follow the rules of attaching clay to clay- nothing dryer than leather hard. Slip will only stick to bone dry pots if it is deflocculated and then sprayed on in thin layers. If you are willing to apply the slip to leather hard clay, you could simply make a slip out of any low fire white clay body.

 

Engobes and commercial underglazes are kind of halfway between clay and glaze- they don't fuse to the point of forming glass like a glaze, but they fuse more than clay, allowing them to adhere to bone dry or even bisque pots. If you must work on bone dry, then you'll have to go this route.

 

Personally, I've found I can get much cleaner, crisper edges to my sgraffito lines by making them on leather hard pots that are on the dryer side of leather hard. I would give this a try, as your pots will also be much less fragile at this stage.

 

You also need to be aware that there are major health issues with carving and scraping on bone dry pots. You are creating a ton of dust that is full of silica and is very bad for your lungs. Working leather hard is much, much safer, from a health standpoint.

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