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Hi, I’m new to the world of clay so forgive me if this sounds like a silly  question. I have a pot I’d like to refire (it’s gone through a cone 10 firing ) it did not have glaze, just a white clay only slip and a bit of oxides. I want to add more slip and oxides and refire but would it be okay to apply a clear glaze on top of an unfired slip?  

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thank you , true, I can just try although now I’m wondering whether the slip would still fall off with the glaze while being fired, I wouldn’t want to damage a kiln 

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slip is just clay and water at its most basic.   clay will not readily stick to bisque so experiments with it seem fruitless to me.   there must be some reason you want to try this, can you tell us?

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You're not going to get a slip to stick to a cone 10 fired pot. You can formulate a slip recipe to be applied to bisque fired work, which is then called an engobe, but getting it to stick to cone 10 fired work is not very likely. The basic fact is that now that your pot is vitrified (not porous) there will be very little mechanical action to keep the slip/engobe affixed to the pot (as the porosity SUCKS the water (and the clay particles) to the pot, and the microscopically textured surface of the pot will help hold the slip on too), and because the slip/engobe is going to shrink as it dries, but your pot wont, the slip will likely shiver right off before you can even get it into the kiln. If you could get it into the kiln with the slip still adhered, theres no guarantees that it still wouldnt shiver off, but the fact that it would likely have a weakened physical/mechanical attachment to the surface of your pot, leaves very little chance that it could develop a chemical bond to the rest of your pot. This of course could be exacerbated by the stains/slips already on your pot.

Simple answer, nope. Complicated solution, that could work, given hours of testing....possible.

When it comes to most things in ceramics that need "fixed" or "done over" again, usually the answer is to just make another.

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Hi, thank you all very much , lots of information there 

i was hoping to achieve the same surface  that is on the first pot; the one  on the left in the picture . The  slip didn’t crack as much for the pot next to it - which is the one I wanted to refire.

i think its best to accept that there’s not much I can do with the piece  & move on. 

thanks again , I really appreciate it 

 

F2D8310E-DE36-4529-9CCD-D8753AA79566.jpeg

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Suze: 
After looking at the images of the pots,  I better understand what you are working with.    
The pots have an intriguing look; appearing to be ancient pots just found under enons of time. 

There are two problems to overcome: 
1. adhesion of the slip to the fired surface during the air drying; this is mainly solved by overcoming the shrinkage stress/strain on the interface between the fired surface and the applied slip layer(s). 
2. adhesion of the fired layer to the applied layer(s) during the firing and afterwards. the slip needs a "glue" layer between its self and the previously fired surface, or the slip should have an additional ingredient that will melt the slip into the substrate while NOT melting the outer surface of the slip into a glossy glaze.  My thought is to add a glue layer using sodium silicate. Adding soda ash or baking soda to the slip might work also.  Trying a sodium silicate layer would not require reformulating your slips. 

Gravity is your primary enemy in this corrective endeavor.  The upper horizontal surfaces have gravity working for success, all the other surfaces require overcoming gravity.

I would make a bunch of small 'test' pieces that replicate the jars you want to reslip and refire.  Make and fire the 'test' pieces as the big pieces were made.  Then try applying a layer of sodium silicate (SSL) on the test piece and then apply the slips on top of the SSL before the SSL dries.  Make the clay slip with a minimum of water; think peanut butter consistency rather than butter milk.  Dry and fire the pieces to your target temperature.  Also try making a slip with a target temp lower than the original cone 10 target, and fire test pieces at that temperature.  Expect some spalling of the new slip and have a plan for dealing with the debris falling on the kiln shelves. 

Once you develop a technique, you can reconsider the need to refire the 'big' pots.  

LT

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