Ian Currie Test Tiles Forums?

[Pieter Mostert]

That almost happened to me too when I tried to preview my post, but luckily my browser had saved what I'd written.

[High Bridge Pottery]

The more grids the better I can't see it anywhere but is alumina decreasing up the tile or increasing? Looks darker at the bottom to me so that should mean most alumina there. The top right glaze would then be most fluid and probably passing most of the bubbles, a little less silica too. The ones below the arc are not even getting their bubbles to the surface.

If the alumina goes the other way then that ruins my theory.

 

I have lost many a post so always ctrl+c it all before posting just in case it dies on me.

[Pieter Mostert]

The more grids the better I can't see it anywhere but is alumina decreasing up the tile or increasing? Looks darker at the bottom to me so that should mean most alumina there. The top right glaze would then be most fluid and probably passing most of the bubbles, a little less silica too. The ones below the arc are not even getting their bubbles to the surface.

If the alumina goes the other way then that ruins my theory.

 

I have lost many a post so always ctrl+c it all before posting just in case it dies on me.

 

Oops, I see I didn't say which direction alumina is increasing. It increases as you go up, so there goes your theory . If you look carefully, you'll see that all the tiles below the arc, except the left hand column, have spots, so they're definitely passing bubbles. I would guess that the most fluid tile is either the 2nd or 3rd one of the bottom row, since increasing additions of iron first increase the melt, and then begin to stiffen it when it gets overloaded.

[Pieter Mostert]

By the way, the electronic version of Ian Currie's 'Stoneware Glaze - A Systematic Approach' which he published on his website under a creative commons licence, can be downloaded here.

 

The chapter on high iron glazes confirms my observation about the effect of alumina.

[curt]

Interesting Pieter, thanks for posting.  I have looked at these tiles a few times since you posted, first trying to understand exactly what was going on and then thinking about what it meant.

 

So alumina is held constant across any given row (eg, alumina is the same on a UMF or mole% basis in cells 1 - 5) but decreases from top to bottom.  Meanwhile, iron is held constant in, for example, cells 1, 6, 11, 16, 21, 25, and 31, but then increased in the next column to the right.  So is it fair to say the increasing iron across a row is proportionally decreasing silica and other fluxes?  Also, can you tell us approximately where the original glaze is on your tile?

 

I am not clear on how these tiles have been fired.  You say the glaze is cone 4, but applied to an earthenware tile (cone 03?) and then to a stoneware (cone 10?) tile.  Have the tiles been fired to these temperatures?  And if so was the glaze designed/expected to work at these temps?  Or were all tiles fired to cone 4 regardless of clay maturity?  Can you clarify? 

 

I think this glaze has serious surface tension issues.  the main tipoff is in cell 5, particularly in the earthenware tile.  See how the glaze has pulled away from the corners and sides of the cell and mounded in the middle, even though it appears to have originally wetted those parts of the cell when applied?  This is apparent in surrounding cells as well, and in the upper right zone of both tiles.  Simlarly, I think surface tension issues are why the bubbles have failed to heal in both tiles.  None of this is surprising given that alumina is the material with the highest surface tension available to us.

 

I suspect that the arc of bubbles is higher up and to the right on the earthenware tile because the iron content of the clay (and/or possibly other ingredients in the clay body) is adding additional flux to the glaze.  Hence the size of the well-melted zone is much larger on the earthenware tile, and the number of cells with good iron spotting in them is much higher in the earthenware tile.  

 

It is also interesting to me that the size of the iron-spots you are getting is very consistent across the tile.  If you look at the earthenware tile, the spots are plain to see in many cells across the tile, but my take is that (coloration aside) those spots are largely the same size and consistency from cell to cell. If you look at my avatar to the left, or at this series of tile shots in my gallery, the size and character of the spots I was getting varied much more from cell to cell.  What the consistency of your iron spots suggests to me that iron component of your glaze, while necessary for spotting, may not be the main glaze ingredient driving the spotting.  Not sure about this. 

 

Finally, I also looked at the glazy.org site and your glaze pics there.  Interesting to see that LESS iron produced a visibly runnier glaze.  Have I got that right?  Could additional iron be making the glaze more viscous?  This would somehow seem to be agreeing with the evidence from your tiles as well.  This seems counterintuitive to me because I see iron as a flux, and more flux should make the glaze runnier.  But maybe that is true in reduction but not oxidation... Hmmm...

[curt]

One other thing: your story of the iron/alumina solubility, and the fact that the white stoneware tile clay body likely has much more alumina than the earthenware one, may explain why the overall cell character of the stoneware tile is darker iron look.

[High Bridge Pottery]

Now that I have a closer look at the bottom rows of the white clay I can see they have glossy reflections and I was arse backwards. The smoothness of the top right squares is interesting. I wonder if you took a cross section would they be full of bubbles or not.

 

There does seem to be a difference between the clay bodies but is it heatwork difference or clay difference. Probably a bit of both. The spots seem to appear where the bubbles disappear, could they be some artifact of the bubbles bursting on the surface.

[Magnolia Mud Research]

Curt was asking about what appeared to be "counterintuitive to me because I see iron as a flux".
 
I suggest looking at the non-bridging oxygens per tetrahedron for the melt (I haven't done the calculations) for each tile.  It could be that the iron is allowing the aluminum to become a network former by charge balancing.  The Fe to Al atomic ratio may also be an informative variable.  
 
LT

[Pieter Mostert]

Thanks for your comments, Curt. To answer your questions, what I'm calling earthenware clay is sold as 'Smooth Red Earthenware', but I've fired large coil pots made from it to cone 4 without any sign of overfiring. I'm not sure what cone the stoneware is designed to be fired at, but cone 10 would be a good guess (unfortunately my supplier gives temperatures instead of cones, if they give any info at all). Both tiles were fired to a bit above cone 4, so the stoneware one is definitely underfired. I'm in the process of formulating some clay bodies that are vitrified at cone 4, which I hope to use these glazes on, and while I really should be testing the glazes on these clay bodies, at least I can get an idea of how things change when you vary alumina and iron (among other variables I've looked at) and then apply that knowledge once I've settled on a clay body.

 

Because I used the wrong kaolin, the glaze I have on Glazy doesn't correspond to any of the ones on the grid. The closest one, both visually and in terms of the oxide composition, is tile 33, but this has SiO2 2.27 and Al2O3 0.33, as opposed to SiO2 2.48 and Al2O3 0.28 for the one on Glazy. Of course, that's assuming the info in the spec sheets is correct.

 

Iron is increasing across each row, so as a percentage of the glaze, everything else is decreasing. If you include iron as a flux, this would mean all the other oxides in the UMF are decreasing, although their ratios remain constant. Iron can definitely act as a flux in oxidation, as this series of test bars shows:

 

Here I just added increasing amount of red iron oxide to a recipe that had the same UMF as Seger's original cone 4 composition. What makes things tricky is that you'll get different numbers of molecules of Fe2O3, Fe3O4 and FeO from the same weight of iron oxide, and since there's probably a mix of these oxides in the glaze, how do you convert from weight to UMF?

 

Regarding iron making the glaze more viscous, I think that this is similar to adding more and more calcium or magnesium to a glaze; at some point the fluxing action will stop and the glaze will become more refractory. I've noticed that excessive iron will make a glaze crawl, although that may also be because of its effect on the glazy slurry, not just the surface tension.

 

I agree that the surface tension is highest in the top right corner. For the unhealed bubbles, I think high viscosity must be playing a role, since I'd expect a high surface tension to smooth out any dimples in the surface.

 

You may be onto something with the white tile contributing more alumina to the glaze. If you moved the tiles in the white grid up one or two rows you'd get a better match with the red grid, although they'd still be slightly darker, so that can't be the whole story. If the glazes on the red tile are getting iron and fluxes from the body, I'd expect them to be darker, particularly since alkalies reduce the solubility of iron, according to Currie's experiment Fe4 on pg 161 and 162 of Stoneware Glazes.

 

There is some variation in the sizes and densities of the spots, though not nearly as large as in your oilspot grid. I suspect that the oxide composition of the cells in your grids vary more than in mine , but even taking that into account, my spots seem quite persistent. I'm working on the theory that the reason I'm getting spots has to do with firing very slowly as I approach the peak temperature. So far I have 4 families of spotty glazes; besides this one, there's the one I posted about in this thread, which has now morphed into this, one with multicoloured spots:

 

and this one. So either my kiln god has a spot fetish, or there's something unique about how I fire. 

[Pieter Mostert]

High Bridge, I'm fairly certain that the spots are due to bubbles bursting. This paper illustrates how bubbles form spots in traditional oilspots (see figure 1). That said, I'm not sure if the bubbles in my glazes are because of the thermal decomposition of iron, given that I fire 100 C lower than the temperature at which this is supposed to happen.

[Pieter Mostert]

Curt was asking about what appeared to be "counterintuitive to me because I see iron as a flux".

 

I suggest looking at the non-bridging oxygens per tetrahedron for the melt (I haven't done the calculations) for each tile.  It could be that the iron is allowing the aluminum to become a network former by charge balancing.  The Fe to Al atomic ratio may also be an informative variable.  

 

LT

 

I'm afraid my knowledge of glass and glazes doesn't expend that far. Do you have a reference where I can read up on this?

[Marcia Selsor]

Hi Marcia,

 

Yes, although Ian did pass away in 2011, his work was very influential and his books including "Revealing Glazes" are still highly regarded.  I think you can get this and his other book on his website by the way at  ian.currie.to  

 

His techniques are very accessible and offer a straightforward way to go beyond simple line and triaxial blending and begin to really understand what makes glazes tick - and discover heaps of new ones!  I am only just now discovering its potential, not only to fix my own existing glazes, but also to use native materials to get some new glazes into the stable.

 

I know that there are a number of people out there who are very familiar with his methodology, and continue to use it or at least recommend it, including some on these very forums.  I think it is too much to hope for that there would be forums dedicated only to his methodololgy, but what I am hoping is that those current practitioners of his method (few though they may be) might have gravitated to a home somewhere in cyberspace to collaborate.   

 

Any other thoughts out there?

 

Cheers,

Curt

Curt,

I have his book revealing glazes. He sent it to me as a present. 

I know his work very well.I have his other book as well.

 

Marcia

[curt]

Just had a look at Currie's Stoneware Glazes.  There is a great discussion on oil spot glazes in the chapter on iron glazes, particularly on pages 166 and 167.  One of the sources he refers to describes oil spotting as the result of bubbles of oxygen being released as red iron oxide decomposes to magnetite.  Reduction firings cause this decomposition to happen too early, before the glaze has actually melted, so no bubbles form, which is why oxidation is generally necessary for oil spots.  He also says there that the thicker the glaze, the larger the spots.  Have you noticed anything like that?  Also had a quick look at your epsilon-iron article, some cool close-up photos there of the oil-spot crystals.

 

Viscosity and surface tension are closely related (see Hamer for a good discussion on surface tension), so Pieter no doubt both are at work in your tiles.  But I am not sure we should expect that bubbles will disappear in a high surface tension glaze any more than crawling will.  Once glaze has separated - either across a valley in crawling or across the circular void of a burst bubble - surface tension is not strong enough to smooth it over, particularly if the glaze is as you say rather viscous.  And the bubbles in your arcs seem fairly large.

 

I would again advocate for using a "6 oclock" mark on your currie tiles.  Once you have applied the glaze to each cell, go back and score through the (still slightly soft) glaze with a needle tool in a short single straight line down to the surface of the bisqued clay body underneath.  You can see this in several of the currie tiles in my gallery (occasionally I forget to put them in doh!).  This mark gives additional information on which cells are melting (or not), how well, and which ones melting well enough to heal over mark.  Sometimes this is not exactly obvious looking at the glaze surface.  And if you can be bothered to go back and do Curries second-layer "striding man" (on pretty much all the tiles in his Revealing Glazes book) that also gives additional information about melting. 

 

I really like those multicolored spots you are getting.  And your post has re-kindled my interest in going to back to look at the oilspots I got recently.

[Joseph Fireborn]

I can attest to the thicker glaze equal bigger oil spots. I use a cone 7 oil spot that if different thicknesses bring out different sized spots. Also another thing I noticed is that if you have unhealed bubbles in your glazes as most oilspot do. You can refire and the bubbles seem to finish bubbling and you get a smoother surface.

[Pieter Mostert]

Joseph, that's good to know, although ideally I'd like all the bubbles to heal in the first firing. Someone's mentioned holding the temperature on the way down to allow the holes to smooth other, but I only held at 960 C in this firing to try get some iron reds, which is probably too low for the oilspots. I know you slow down the cooling, but is this only after first dropping quickly from the top temp, or do you go slow all the way down?

 

The glaze this grid was based on shows the effect of different thicknesses: https://glazy.org/recipes/8010

I dipped these 4 times, each time covering less of the tile, so that thickness increases from left to right. Here's my theory why thicker glaze layers produce larger bubbles: Microscopic bubbles join up with each other to form larger and larger bubbles, until the bubbles extend beyond the surface of the glaze, at which point they burst. The thicker the glaze, the larger the maximum radius of a bubble that can fit inside the glaze layer, and thus the larger the maximum spot you get.

 

Curt, I'll have to get hold of a copy of Hamer and Hamer. For this test, I think the striding man may have obscured what was happening with the spots, but I can see how using it and the 6 o'clock mark would be useful in general, especially if the glazes aren't applied as thick as they were here. Looking forward to your next oilspot test.

[Magnolia Mud Research]

Pieter,

Pieter Mostert Posted 06 August 2017, 02:21 PM
"I'm afraid my knowledge of glass and glazes doesn't expend that far. Do you have a reference where I can read up on this?"
 

Here is a quickly developed list of sources that might be useful:

Mysen, Bjorn, & Pascal Richet.  "Developments in Geochemistry 10, Silicate Glasses and Melts - Properties and Structure" Elsevier, 2005 (ISBN 0444520112)  This book covers just about everything.
*|*
Shelby, James E. "Introduction to Glass Science and Technology 2 ed."  Royal Society of Chemistry. (ISBN 085404639)
*|*
Lecture notes from an introductory college course on glass for ceramic engineering students:
Structural Theories of Glass Formation
http://web.mst.edu/~brow/PDF_structure1.pdf
http://web.mst.edu/~brow/PDF_structure2.pdf
*|*
Notes and reading topics for the 2013 online course "Atomistic Modeling of Glass Structure & Glass Properties"
pre-lecture readings:    http://www.lehigh.edu/imi/teched/AtModel/Lecture_3_reading_geochematerials.pdf  

http://www.lehigh.edu/imi/teched/AtModel/Lecture_3_reading_structure_silicate_glass.pdf    

http://www.lehigh.edu/imi/teched/AtModel/Lecture_3_Assignment_Micoulaut_Atomistics_Glass_Course.pdf   

the formal lecture presentation:
http://www.lehigh.edu/imi/teched/AtModel/Lecture_3_Micoulaut_Atomistics_Glass_Course.pdf

 
*|*
A presentation from:
GEO-RAMAN Xth MEETING
11-13 JUNE 2012, Nancy (France)
sponsored by European Mineralogical Union (EMU)
title:  Raman Spectroscopy of Silicate Glasses and Melts in Geological Systems presented by Stephanie Rossano & Bjorn Mysen
http://georaman2014.wustl.edu/previous/2012/georaman10.uhp-nancy.fr/planchesInternationalschool/015%20SilicateGlassesAndMelts-S-Rossano.ppt.pdf   
*|* 
The applications of glass and the structure of glass from molecular dynamics seminar notes presented by
Dr. Gavin Mountjoy, University of Kent, Canterbury, UK
http://www.kent.ac.uk/physical-sciences/staff/profiles/gm/MD_glass_seminar.pdf 
*|*

My experience has been that the details of the physics and chemistry of silicate melts (aka "glazes" in studio potter lingo) is discussed best in the domains of igneous petrology and materials science disciplines.  The Seger model is not wrong so much as it does not account for about a hundred and twenty years of progress in understanding the structure of a silicate melt at the atomic level.  Both models just count species and use the ratios of species as variables, but the most recent models do a better job predicting physical and other properties than Seger's model.

 

Currie's scheme of a grid test is a very useful technique; the scheme provides a large amount of data in a small package that almost eliminates the position in the kiln variable associated with individual test tiles; and the scheme can be applied in a way to minimize the leftover glaze(s).
  
  
LT

[Joseph Fireborn]

Joseph, that's good to know, although ideally I'd like all the bubbles to heal in the first firing. Someone's mentioned holding the temperature on the way down to allow the holes to smooth other, but I only held at 960 C in this firing to try get some iron reds, which is probably too low for the oilspots. I know you slow down the cooling, but is this only after first dropping quickly from the top temp, or do you go slow all the way down?

 

Currently I drop 400F per hour from cone 6(2232F with 20minute hold) to 1750F. So I don't instantly drop, but I do drop pretty rapidly. I have tried both and I didn't seem to get different results. I have also tried the holds on the way down after dropping 100F from cone 6. However I still had the same issues. The best results were a really hot cone 7 firing, almost 8 by holding at 7 for a long duration. This gave me the smoothest surfaces. From what I understand the iron bubbling to get the oilspots starts happening right past 2250F. So I am not sure how exactly your getting these spots at cone 4, but maybe I am misunderstanding how exactly everything works. Are you firing really fast to cone 4 which enables you to reach the same temps as cone 6(usually 2232F) but not getting the equivalent heatwork?

 

Either way, knowing that a beautiful piece comes out with bubbles can just be refired is a nice piece of mind while experimenting with this process.

[Pieter Mostert]

Thanks LT! I'm looking forward to going through those notes.

 

Joseph, it's a mystery to me why I'm getting the spots, since I fire really low and slow to get to cone 4. My max temp was 1129 C, whereas the iron bubbling in traditional oilspots is only supposed to start at about 1230 C (depending who you ask). The major difference is that my glazes have boron, so that might somehow be catalysing the process, or it could be some other process happening. But the fact that glazes like the ones I'm getting are quite rare at mid-fire temps, seems to indicate that there's something about the way I fire that makes a difference. I've seen papers that mention high iron boro-silicate glasses are prone to phase-separation, but until I brush up on the necessary chemistry, I can't say if this is relevant.

[curt]

Pieter, something I posted in a similar thread of yours last October:

 

Phase diagrams for FeO-SiO2-Al2O3 show a eutectic as low as 1088C. This occurs with (approximately) 12 Alumina, 40 Silica and 48 Iron, an entirely possible combination.

 

This is FeO but I will look for Fe2O3 phase diagram as well.

 

The main message is that iron decomposition could be taking place at lower temps?

[Pieter Mostert]

It could be, but I'm a little hesitant to draw conclusions about glazes based on phase diagrams.

[curt]

It could be, but I'm a little hesitant to draw conclusions about glazes based on phase diagrams.

 

Agreed.  It was not so much a conclusion, but rather more of an idea about a path for further exploration to help solve your mystery.  My take on glaze eutectics is that the more oxides you have, the more complex eutectics have the opportunity to form, and the lower the temperature at which everything melts. 

 

Thinking more about it, I agree with you that the boron could be the catalyst.  Boron starts melting at around 840 C and is a glass by 950 C, so (depending on how much boron you use) this could be getting the overall melt going way earlier than typical midfire temperatures. 

 

I wonder if this also means that oil spots could appear in a reducing environment if the temperature at twhich the melt really got going was lower than when the iron products in question started to decompose?

[curt]

Pieter,

Pieter Mostert Posted 06 August 2017, 02:21 PM

"I'm afraid my knowledge of glass and glazes doesn't expend that far. Do you have a reference where I can read up on this?"

 

Here is a quickly developed list of sources that might be useful:

Mysen, Bjorn, & Pascal Richet.  "Developments in Geochemistry 10, Silicate Glasses and Melts - Properties and Structure" Elsevier, 2005 (ISBN 0444520112)  This book covers just about everything.

*|*

Shelby, James E. "Introduction to Glass Science and Technology 2 ed."  Royal Society of Chemistry. (ISBN 085404639)

*|*

Lecture notes from an introductory college course on glass for ceramic engineering students:

Structural Theories of Glass Formation

http://web.mst.edu/~brow/PDF_structure1.pdf

http://web.mst.edu/~brow/PDF_structure2.pdf

*|*

Notes and reading topics for the 2013 online course "Atomistic Modeling of Glass Structure & Glass Properties"

pre-lecture readings:    http://www.lehigh.edu/imi/teched/AtModel/Lecture_3_reading_geochematerials.pdf  

http://www.lehigh.edu/imi/teched/AtModel/Lecture_3_reading_structure_silicate_glass.pdf    

http://www.lehigh.edu/imi/teched/AtModel/Lecture_3_Assignment_Micoulaut_Atomistics_Glass_Course.pdf   

the formal lecture presentation:

http://www.lehigh.edu/imi/teched/AtModel/Lecture_3_Micoulaut_Atomistics_Glass_Course.pdf

 

*|*

A presentation from:

GEO-RAMAN Xth MEETING

11-13 JUNE 2012, Nancy (France)

sponsored by European Mineralogical Union (EMU)

title:  Raman Spectroscopy of Silicate Glasses and Melts in Geological Systems presented by Stephanie Rossano & Bjorn Mysen

http://georaman2014.wustl.edu/previous/2012/georaman10.uhp-nancy.fr/planchesInternationalschool/015%20SilicateGlassesAndMelts-S-Rossano.ppt.pdf   

*|* 

The applications of glass and the structure of glass from molecular dynamics seminar notes presented by

Dr. Gavin Mountjoy, University of Kent, Canterbury, UK

http://www.kent.ac.uk/physical-sciences/staff/profiles/gm/MD_glass_seminar.pdf 

*|*

My experience has been that the details of the physics and chemistry of silicate melts (aka "glazes" in studio potter lingo) is discussed best in the domains of igneous petrology and materials science disciplines.  The Seger model is not wrong so much as it does not account for about a hundred and twenty years of progress in understanding the structure of a silicate melt at the atomic level.  Both models just count species and use the ratios of species as variables, but the most recent models do a better job predicting physical and other properties than Seger's model.

 

Currie's scheme of a grid test is a very useful technique; the scheme provides a large amount of data in a small package that almost eliminates the position in the kiln variable associated with individual test tiles; and the scheme can be applied in a way to minimize the leftover glaze(s).

  

  

LT

 

LT thanks for this amazing reading list.  I have spent some time with Shelby, very good value.  Will trawl through the rest in days ahead. 

 

The only thing that bothers me a little about trying to apply lessons from the glass guys is that they do not try to make their glass batches on top of a ceramic mass underneath which they are trying to mature at the same time!

 

To your point about igneous petrology, I found a paper recently on magma recently that seemed like they could have been talking about glaze!  A silicate melt which heats and cools and gets affected by all sorts of alkalis, metals, etc. along the way.  Surprising parallels.

[Joseph Fireborn]

Joseph, it's a mystery to me why I'm getting the spots, since I fire really low and slow to get to cone 4. My max temp was 1129 C, whereas the iron bubbling in traditional oilspots is only supposed to start at about 1230 C (depending who you ask). The major difference is that my glazes have boron, so that might somehow be catalysing the process, or it could be some other process happening. But the fact that glazes like the ones I'm getting are quite rare at mid-fire temps, seems to indicate that there's something about the way I fire that makes a difference. I've seen papers that mention high iron boro-silicate glasses are prone to phase-separation, but until I brush up on the necessary chemistry, I can't say if this is relevant.

 

Yea I have no idea. Either way whatever your doing is excellent. I am not a person who really cares to much about the purity of the chemical process. Like making something look like reduction when it was actually electric. I am not a purist in that matter. If you can get beautiful oilspots at cone 4 then who cares! Do it. Those look really nice. I can't wait to see them on a piece. Are you going to do the traditional oilspot bowl! to demonstrate it?

Edited August 11, 2017 by Joseph F

[Pieter Mostert]

Curt, I don't see any reason why you couldn't get oilspots the way you suggest. If you fired in oxidation up to the point where the glaze was melted enough to hold bubbles and then reduced, you'd be reproducing the thermal reduction of Fe2O3 (I think...). However, I suspect you'd be limited in how much higher you could fire before the spots dissolved back into the glaze.

 

Concerning the boron, it's worth keeping in mind that on the old thread of mine you mentioned, Neil posted a cone 6 oilspot recipe which only has 0.024 B2O3 (UMF). In my Currie grid, B2O3 is 0.09, which is still on the low side for cone 4, although the other families of spotty glazes I'm working on are higher at 0.32, 0.33 and 0.38. Not sure what to make of that.

 

Joseph, I've started making a bunch of small bud vases to test glazes on, like you do. For most of my pottery life I've been more interested in form than glazes, so now I'm in the unusual position of having to decide on pots for my glazes, rather than glazes for my pots (although I've been using terra sigillata for my large coiled pieces for a while now). I think oilspot glazes really suit the shape of Jian tea bowls, but I'd need to get myself a wheel if I wanted to do something like that.

[Joseph Fireborn]

Joseph, I've started making a bunch of small bud vases to test glazes on, like you do. For most of my pottery life I've been more interested in form than glazes, so now I'm in the unusual position of having to decide on pots for my glazes, rather than glazes for my pots (although I've been using terra sigillata for my large coiled pieces for a while now). I think oilspot glazes really suit the shape of Jian tea bowls, but I'd need to get myself a wheel if I wanted to do something like that.

 

The little vases are so great. I can't wait to see one in oilspot! I agree the Jain teabowls look so cool. I want to make one eventually and put on the oilspot super thick.