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rayaldridge

Making Slips More Reactive

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Lately I've been trying to do some new stuff with slips.  I make my slips by using my porcelain trimmings, mixed with stains and/or oxides.  I've experimented a bit with adding titania to some slips, which gives a different surface to some glazes applied over the slip-- glazes that are on the edge of developing matte surfaces will go matte reliably over the slips.

 

But I'm wondering if I could make slips more reactive or to put it another way, more interactive with both body and glaze by adding small amounts of flux to them... say 5 % of gerstley borax.

 

This might not be a good idea when slips need to retain a hard edge, as in some resist work, but an example of what I'm trying to do is to spray bands of colored slips onto pots and have those bands interact and fuse in an interesting way.

 

Has anyone experimented with fluxed slips made from a porcelain body, and what were the results?  Or do you know of potters who have explored this area?

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Well, I suppose one could use glazes in the same manner as I plan to use fluxed slips, especially single fired glazes, but the rationale behind the idea is that slips made from the porcelain body would fit leatherhard pots precisely, and be easy to control.  For example, it can be a bit of a struggle to keep an exterior glaze from mingling with a liner glaze, if you don't want it to, but with a colored slip, it's easy to wipe it off the lip and interior of the pot.  Then after bisque the exterior glaze can get much of its color from the slip, and leave a liner glaze of similar hue undisturbed. There are also many decorative techniques that work best with slip on leatherhard pots... combing and so on.

 

Lately I've been working with a fake ash glaze I developed that can pick up a lot of color from the underlying slip, because it is such a reactive glaze.  That's really the genesis of my question.

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Guest JBaymore

If glazes are undersupplied with silica... they end to "steal" that from the underlying body.  What is happening is that the interface zone is becoming a more significant part of the whole glaze layer.  In picking up stuff from the body... it is picking up all the chemistry from the body.

 

So look for glazes that are lower limit to undersupplied with silica as a starting point.  BUT... you are trading glaze durability for the "reactivity".

 

There is a reason the glazes on bathtubs, sinks, and toilets look like they do. ;)

 

Also try virtreous slips under glazes for more interrplay.  And spraying thin layers of glazes.

 

best,

 

..........................john

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Have you looked into engobe recipes and pictures?  That sounds pretty much like what you're talking about, as an engobe is somewhat in between a slip and a glaze.  It's applied on greenware or bisque, always under glaze and not on top of it.

 

Here's an article from CAD:

 

http://ceramicartsdaily.org/ceramic-supplies/ceramic-raw-materials/slip-engobe-or-underglaze-robin-hopper-demystifies-three-common-pottery-materials/

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It's not so much the glazes that I'm asking about.  Certainly the fake ash glaze would not be appropriate for the interior of domestic ware, but that why I mentioned liner glazes, which I almost always use unless the exterior glaze is durable and contains no potentially leachable toxic elements.

 

You used the term "vitreous slips," and some of my titania slips are composed not of my porcelain body, but of the usual suspects, and can be thought of, I suppose, as underfired glazes.  What I'd like to know is if anyone here has worked with slips made from the porcelain body they're using, with added flux.  I'll be trying this out shortly, and can report my experiences, but I haven't found any work that is explicitly described in this manner (though it seems impossible that this has not been tried extensively.)  Looking at the composition of porcelain bodies in the higher ranges, it seems clear to me that these are not terribly far from glazes; the Cone 8 porcelain I use is translucent in thin areas.  To me, the advantage of making slips from the body is perfect fit.  With porcelain, color is not affected by the iron content of most stonewares, so to me it seems a good vehicle for these experiments.

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kswan, these would not be engobes, which generally have little plastic clay in them.  A slip made from the body, with a percent or two of colorant and, say, a little gerstley borate, would be used on leatherhard pots.  The advantages that I see are perfect fit, and relative economy.  I have enough dry trimmings in my wheel right now to make dozens of tests.

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If you wanted interaction between the two strips of slip, perhaps you could spray with an acidic substance, as in with the nicotine method of slip diffusion if that is the right word. 

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Are you wanting to make a porcelain slip that could in theory produce a similar effect to a wood ash glaze or is that what you mean by 'reactive'? Really sort of melting and crawling the glaze?

 

Porcelain is quite similar to a glaze that you can throw with :D Do you know the recipe of your body? Its interesting to hear about Titanium slips. Never tried that before but I will be now.

 

I am trying to think of things to put in the porcelain that would really impart some change into the glaze but I am not sure  :mellow: Maybe some larger chunks of frit/GB could be interesting or even a bit of feldspar.

 

I would start by getting slips and adding increasing amounts of different flux till you get into ~50% flux with slip. See what happens with your glazes, go from there.

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Guest JBaymore

Using the body as a base for a slip is the "old standby" of the more primitive folk potter.  So yes that will work OK.... particularly with porcelain.

 

Granular raw colorant materials will unevenly disburse the material into the overlying glaze.  So try that.  Granular rutile is a great one for this.  Even straight rutile (impure titanium ore .... with iron) is great for "reactivity".  Go find a rust car shell and scrape off some rust.  Crush it...... don't sieve it much and use it as "iron oxide" in the slips. Find rocks that contain ceramic colorants... crush them, and add to the slips.

 

best,

 

....................john

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Thanks, everyone.  Interesting ideas.  I guess I'll just have to try it and see what happens. 

 

John, good point about folk potters, who often glazed their wares by combining wood ash and the body clay.  I'm thinking about some of the old family potters in the SE, who made some wonderful pots that way.  There was a limited palette, colorwise, but still...

 

Porcelain should be easy; it's closer to a glaze than  most stoneware clays.  I won't use ash or calcium, probably, because I like clean color and the calcium has a bleaching effect that I find somewhat frustrating.  The fake ash I mentioned upthread I like pretty well, but so far the best color I've gotten out of it is a pale chartreuse/straw.  I'm not a fan of iron in oxidation, so that limits my choices quite a bit.

 

I'll probably try a little boron in the slip to start with. 

 

I have a feeling that I'm moving in the direction of single-fired ware, which will be a new thing for me.

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Update:

 

I made up a few different slips from my porcelain body (Standard 130) plus 5% gerstley borate, and added varying amounts of Mason stains to them (1 to 2%) mostly blues and greens.

 

This was sprayed onto test tiles using a mouth atomizer, in bands without distinct borders.  I was hoping for subtle gradations in color, but after bisque these tiles were pretty pale.  I glazed them with various glazes I had on hand, and I got the most interesting result from a glaze modified from one of the recipes in John Britt's midrange book.  This was a glaze with modest amounts of lithia and titania.

 

Since I've been limited to oxidation firing, I've learned to love titania.

 

Here's the test:

 

post-65900-0-83577500-1426024968_thumb.jpg

 

Click the thumbnail to see a better image.

 

The slips developed much more color after hard firing (Cone 8).  The unglazed surface is like a very dry matte, but it did not stick to the shelves at all.  I may try the next round with more boron, and I'd better put some food coloring in the slip so I can see where it goes when I spray it on.  Presently the stains do not tint it adequately when wet.

 

You can see the unglazed slip at the bottom of the tile.

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Guinea, I'm pretty stuck on porcelain at this point, but when I used to use stoneware, I liked that effect a lot, especially since I was firing in fuel-burning kilns with plenty of reduction.  In the early years of my career, I used a dug-from-the-ground stoneware that was so full of roots and hematite nodules that I had to force it through an extruder with a stainless screen to get the big stuff out ( I bought it wet, which was the only way it was available.  Other ancient potters from the SE may remember Mrs. Hamm near Tuscaloosa, the last of a family of traditional potters, who sold the clay.)  That was actually a great clay that fired grey in Cone 10-11 reduction, and the remaining hematite nodules melted out in long trickling streaks.

 

But I have a titania matte with cobalt that greatly resembles granite when fired-- green crystals on a blue field, and it even sparkles like granite in the sun.

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Hi I tried to look up  "titania", comes up as a character in W. Shakespeare's play. What is the abbreviation for please. Thanks Jolie

 

Add the word chemistry after your search for Titania to point google in the right direction.

 

'Titanium dioxide, also known as titanium(IV) oxide or titania'

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What High Bridge said.

 

It's kind of oldschool to refer to oxides in this manner, but it's fewer letters when writing stuff down.  So I call alumina oxide alumina, titanium oxide titania, and so forth.  Sorry for the confusion.

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Update:

 

I made up a few different slips from my porcelain body (Standard 130) plus 5% gerstley borate, and added varying amounts of Mason stains to them (1 to 2%) mostly blues and greens.

 

This was sprayed onto test tiles using a mouth atomizer, in bands without distinct borders.  I was hoping for subtle gradations in color, but after bisque these tiles were pretty pale.  I glazed them with various glazes I had on hand, and I got the most interesting result from a glaze modified from one of the recipes in John Britt's midrange book.  This was a glaze with modest amounts of lithia and titania.

 

Since I've been limited to oxidation firing, I've learned to love titania.

 

Here's the test:

 

attachicon.gifreactive slips.jpg

 

Click the thumbnail to see a better image.

 

The slips developed much more color after hard firing (Cone 8).  The unglazed surface is like a very dry matte, but it did not stick to the shelves at all.  I may try the next round with more boron, and I'd better put some food coloring in the slip so I can see where it goes when I spray it on.  Presently the stains do not tint it adequately when wet.

 

You can see the unglazed slip at the bottom of the tile.

 

Do you mind sharing the percentages of titanium and boron you think started to arrive at what you were shooting for

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I used about 5% of gerstley borate for the boron and 8% of titanium dioxide in my slips.  My favorite glazes also rely on boron and titania too, so probably the interaction is complex. 

 

I have one slip with no colorants other than 15% titania, which under a clear glaze over porcelain gives pale cream and yellow colors, but I don't use it for that purpose.  I use it with colored glazes that have a tendency to develop crystalline surfaces.  The titania in the slip kicks the crystal development, which yields a color and surface texture difference.

 

Here's an example:

 

gallery_65900_865_665.jpg

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ray,  years ago when i was making mostly thrown pots with colored slips made from the clay body, i tried titanium in the glaze because i thought it would give me something like rutile does, namely, hare's fur streaking.  is that what you are seeing in your experiments?  have you gone the single fire method yet?

 

three or four days of glazing the greenware i brought up from florida has made me even more of a single fire potter.  stuff just does not act right when it is bisque fired.

 

your glazes are so beautiful and the colors so soft that i would love to use them on thrown work.  cannot use them on my normal highly textured slabs.  need transparency for those to look good.

 

got any recent pictures, maybe with the fake ash glaze?

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A slip made from the body, with a percent or two of colorant and, say, a little gerstley borate, would be used on leatherhard pots. 

I had heard somewhere that gerstley borate can dull colourants. Is this true, and how would you get around that?

Joe

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ray,  years ago when i was making mostly thrown pots with colored slips made from the clay body, i tried titanium in the glaze because i thought it would give me something like rutile does, namely, hare's fur streaking.  is that what you are seeing in your experiments?  have you gone the single fire method yet?

 

got any recent pictures, maybe with the fake ash glaze?

 

I do get streaking in glazes with extra titanium, and I like the effect better than rutile, because the titanium doesn't have the heavy iron content.  My impression is that titania in the slip does not have the same effect, since slip stays put, and hare's fur streaks can't develop unless the glaze moves.

 

My use of titania in slip is to kick off certain surface effects.  In the past, I've used it with clear glazes that sometimes develop a matte surface if cooling is prolonged.  The glaze seems to pick up enough titania from the slip to go opaque and matte over the slip.  If I resist the slip, or carve it away, I get a contrast in surface and color between the slip and the porcelain body.

 

I have not yet tried single-firing with any of these glazes, though of course when I was making salt-glaze ware I single-fired.

 

Here's a recent little bowl with ash glaze over a titania-bearing glossy glaze, over titania-bearing slip.

 

gallery_65900_888_19973.jpg

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