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Hi I'm fairly new to ceramics, so forgive if I seem a bit clueless.

 

I am using commercial underglaze on porcelain but am finding the consistency a bit too watery and would like to experiment with a thicker mixture.

 

Could I simply make a slip from dry powdered porcelain + water and mix this with the underglaze to thicken? I realise it would lighten the colour as the porcelain is white, I don't mind this.

 

I'm just looking for a simple way of thickening the mix and adding some variation as I don't want to get too technical at this early stage by creating my own recipe with ball clay, fluxes etc.

 

I also have some oxides that I'd like to add to my simple clay body + water slip. Would this work or is it necessary to have all the other ingredients?

 

Thank you for any advice

 

Emma

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Adding oxides or stains to dry clay body and adding water makes a good slip. I also sieve my slips to make sure the oxides/stains are thoroughly mixed. For stains, I usually use a ratio of 10% stain to powdered clay body. For oxides, it will depend on the oxide -- especially the cobalts which are very strong and you only need a small amount.

 

You'll find a lot of good information at Vince Pitelka's website: http://iweb.tntech.edu/wpitelka/syllabi-handouts/handouts-info.htm

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Thanks for your responses and the link.

 

I'm using Bath Potters high fire stains.

 

Another thing I was wondering, if I used Underglaze Flux ( http://www.scarva.com/en/Scarva-Underglaze-Flux/m-2073.aspx  ; add between 25-33% to make a powder stain into an underglaze) and added water, could I possibly make an underglaze which self-glazes when high fired? 

 

At the moment the underglazes I'm using (scarva nano) come out with a subtle gloss-sheen after high firings which I've been told is due to the flux in the underglaze.

 

 

Many thanks

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Thanks for your responses and the link.

 

I'm using Bath Potters high fire stains.

 

Another thing I was wondering, if I used Underglaze Flux ( http://www.scarva.com/en/Scarva-Underglaze-Flux/m-2073.aspx  ; add between 25-33% to make a powder stain into an underglaze) and added water, could I possibly make an underglaze which self-glazes when high fired? 

 

Ask the supplier, but I suspect not.

Just as you wouldn't paint your walls with straight pigment cut with a little bit of binder, you don't glaze ceramic with that much stain. It's expensive, and would be prone to leaching and/or discolouration. Ceramic stains tend to be quite refractory, and they benefit from the addition of a little bit of flux like your supplier recommends to help it melt to the pot, instead of dusting away. Flux by itself doesn't make a strong glaze that would be suitable for something like tableware. You need other ingredients to form glass (silica) and for durability (alumina).

 

What temperature are you working at, is function a concern, and what sort of surface are you looking to achieve?

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Okay, I was thinking I might have to start a new thread on the idea of making slips more reactive.  In late years I've been making slip by reconstituting my porcelain body (from trim scraps) and adding stains and oxides for color. 

 

But since I'm currently firing in an electric kiln at 8, I have to work pretty hard at getting subtle and beautiful glaze effects, the kind that I was able to get in a fuel burning kiln pretty easily.

 

Some of my slips have added titania to get different surface effects, but lately I've been wondering if it would be useful to add a little flux to the slips, in the form of gerstley borate, in order to get a more reactive interface between slip and glaze.  I wouldn't do this with slips that had to hold a hard edge, as in some of my slip resist work.  I had in mind the possibility of subtle gradations of one colored slip into another and so on.  Recently it's occurred to me that control of color can be almost effortless with slips applied to leather hard ware, since the slip can so easily be wiped away from rims and other places where I don't want the color to spread.

 

Has anyone experimented with this approach to surface decoration, or know of potters who have, and what were the results?

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Royalties,

 

If you look at my post titled under the title "Cobalt Wash." In the glaze forum, I list recipes for colored washes. You can also make colored slip. There are several recipes. I don't have access to any now but sure you can find some with an internet search.

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  • 2 weeks later...

Thanks for your replies. My work isn't functional and I want a really dry surface, preferably translucent so you can see the colours layering up underneath.

 

I've decided to try an egobe recipe as I have access to ingredients now and want to be able to use it on bisque ware. However, as I slab build and have a lot of off cuts, I want to use my own clay body to make it. (I'm using grogged porcelain: http://www.scarva.com/en/gb/Scarva-Grogged-Porcelain/m-67.aspx)

 

When I'm looking at recipes, is there an element I can substitute for my own powdered clay?

 

I've read that altering the amount of flux in the slip will alter the surface from glossy to matte. Does anyone have a recipe for white engobe which produces a very dry finish when fired to cone 6?

 

Any help much appreciated, thank you.

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emma, if you look at the thread I started in the clay and glazes forum, you can see what I did to make a colored slip from my porcelain body.

 

In short, I added 5% gerstley borate to the body (in the form of dry trimmings) plus 1 to 2% stain.  This gave a dry surface on the matured body.  There was no gloss on unglazed slipped surfaces, but visually the surface seemed dense.  You could substitute a boron based frit for the gerstley borate.

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I doubt it will work as well on bisque, because porcelain has such a high shrinkage.  It would probably work if you were to powder and calcine most of the body, but I suspect that would be a lot more work than just finding a good engobe recipe and making your coating from stuff that wouldn't shrink so much.

 

Is it necessary to use the stuff on bisque?  Working with slip on leatherhard ware is really a lot of fun, and very versatile.  It opens up all manner of interesting decorative techniques, and is very easy to control.  You can wipe it off, use resists, carve through it, etc.  I'm not sure what you can do with an engobe on bisque that you couldn't do with leatherhard ware.

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when you are early in your career, your imagination is sometimes on overdrive and it is hard to think in a reasonable way when a problem comes up.  i believe the current term is that you are "overthinking".the problem.

 

layers of different colors will soften but not mix with each other.  think of adding slip as just thickening the original wall of clay.  a single color layer is not much of an addition, and each color only adds the thickness of the layer of slip at a time.  it is very unlikely that your piece will deform from adding reasonably thick slip one layer at a time.  

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emma_19,

 

You just need to let the layers dry some between coats.  You should make your self some test tiles with your underglazes, single coat, multi-coat, different layers on top of each other, and with your clear on top.  This will answer many of your questions.

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