Results for Min (and everyone else) on unknowns

[MFP]

Results of 50 Colemanite mixed with 50 of each unknown substance we did the LOI test on. I don't think this is going to reveal much. Please see PeterH's glaze he posted with the three materials. They are in order. 1, 3, 5

[Min]

So you are sure that it is colemanite that the 3 unknowns used in the tests above were mixed with right? Or is the colemanite in question too? If it is definitely colemanite then I think you could rule out plastic vitrox as being one of these 3 unknowns. Also think you could rule out clays. 

For the other tests from this thread, is this the recipe you used: 20 Frit 3134, 21 EP Kaolin, 27 mystery material, 32 silica?

edit: I took the liberty of editing the title of this thread, think we need all the ideas we can get to try and untangle this!

[MFP]

I am absolutely sure it was colemanite. There was some contamination from the inside of the can flaking off.....I did not realize how much was in there until I got everything mixed up.  So...the brown is from the rust. Interesting that #1 resulted in green. There was more of a difference using that glaze PeterH posted.

[MFP]

Here is the PeterH glaze recipe for differentiating between dolomite and calcium carbonate. I think we may have done that with 1 and 3.....5 is much more matte.

The difference between dolomite and calcium carbonate in a glaze

These glaze cones are fired at cone 6 and have the same recipe: 20 Frit 3134, 21 EP Kaolin, 27 calcium carbonate, 32 silica. The difference: The one on the left uses dolomite instead of calcium carbonate. Notice how the MgO from the dolomite completely mattes the surface whereas the CaO from the calcium carbonate produces a brilliant gloss.

 

[MFP]

[Min]

2 hours ago, MFP said:

I think we may have done that with 1 and 3.....5 is much more matte.

Sounds reasonable, as they both had about the same LOI didn't they. Since the test piece with what you think is calcium carb should craze more than the dolomite sample you could stress test them just to double check. Heat them up in the oven at 325F then drop them into ice water and look at the crazing pattern, if they don't craze then try it at 350F but do both of them. In theory the calcium carb test should have finer crazing lines than the dolomite one.

[MFP]

1 and 5 had about the same LOI.  3 did not have any loss despite fusing. Looking at these glaze results....I am wondering if 1 is the calcium carb, 3 is the dolomite and 5 is Bone ash or a feldspar like Kona F4

[Min]

If #3 didn't have any LOI then it won't be calcium carb or dolomite. 

Very close  chem  between using calcium carb and bone ash.

Comparing calcium carb version with one using F4, note the LOI for F4 in the blue reference box, nearly zero so that doesn't fit with your LOI test.

[MFP]

Well....the 1 and 3 results with Peter's glaze recipe are consistent with one being calcium carbonate and the other dolomite---the glossier one being the calcium carb. .  The really matte appearance of 5 makes me wonder.  Like I said....the glazes we used in those days were not that special. But I am still stuck on the physical appearance of 5,....the only material that looks like it is bone ash.  I think in the next bisque, I will put in some bone ash and see if it turns out the same.  Can you think of any other material that is kind of grainy like that? And has trace iron...remember...it turned pink. But if bone ash is comparable to calcium carbonate.....then 5 should be glossy right?    Maddening

I am afraid all this uniform glaze theory is still a lot of Greek to me but I really do appreciate your sharing it with me.  Someday hopefully I will understand it

Do you happen to have a high calcium clear glaze that likes Mason stains?

[Min]

3 hours ago, MFP said:

Can you think of any other material that is kind of grainy like that? And has trace iron...remember...it turned pink

Did you use Cornwall Stone aka Cornish Stone back then? Raw colour of it ranged from an aqua blue to off white, it definitely clumps up in storage, is somewhat grainy and contains iron. Chemistry for it can vary greatly. Spodumene is sort of like fine salt grains but doesn't clump up in storage, the spodumene from years ago made really good shino glazes, it contained more iron than the spodumene available now.

Could 3 be barium carb? If one of them is bone ash then making up an iron red glaze from a recipe with that (or tricalcium phosphate) would give you more info but the problem with this is many of the iron reds need a slow cool to develop the iron red colour and with a manual kiln that can be tricky.

3 hours ago, MFP said:

Do you happen to have a high calcium clear glaze that likes Mason stains?

Since it's really high in calcium it will craze on some clays.

^6 Clear Base Glaze from Forrest Gard May 2016 Pottery Making Illustrated

Wollastonite 30

Ferro frit 3195 30

EPK 20

Silica 20

100

For Emerald Green, add 4% Copper Carbonate. For Cobalt Blue, add: 1.5% Cobalt Carbonate. For Turquoise, add: 8% Mason Stain #6374. For Amethyst Purple, add: 5.0% mason Stain #6304, 0.5% Cobalt Carbonate.

[MFP]

Yes....I was suspicious that 3 was barium carbonate. I used a lot of it in a celadon glaze I used....a lot . I was wondering if it started to fuse at that temp, I think my memory is going....I thought digital fire said it would not lose mass on LOI but that could not be possible because it is a carbonate....perhaps I measured it incorrectly.  It also is somewhat lumpy and likes to form balls. 

Cornwall stone is a possibility......it was around then but I cannot remember using it in any glazes.  I remember using Kingman and Kona F4.

Thank you for the clear recipe. I will have to buy the frit. Who has the cheapest tin? I found a ceramic supply in PIttsburgh (my home town) that has all kinds of exotic materials....for example it has pyrophillite talc, Texas talc and all kinds of weird things. It's tin price is pretty good.  I did find a cream breaking rust that takes half zircopax. 

Turns out there is a fourth material to identify,  Mark was sure that it was zircopax.....NOT.....when side by side.....it is clear that it is NOT zircopax. It had a slight opacifying effect and made the glaze somewhat more glossy. 

I also have a coffee can full of something that is either zircopax or tin. It opacified in the recipe like crazy. So I will have to use it in a tin recipe to see what it does. I am pretty sure it is zircopax. 

I have to find my damn old glaze book. I remember finding it and putting it in something special so I would remember where it was....right....now everything is piled up against a  wall where I can't get to stuff.

I had another thought.......since it is clear that the colemanite was such a powerful flux that we cannot differentiate between materials....I am wondering what else we could mix this with 50/50 that at least would tell us whether we were dealing with a flux or a stiffener.  Like 50 silica maybe?

This last fire only yielded about four useful glazes. So I will be doing another glaze test fire.  It was very interesting seeing how the different porcelains took the glazes. To my great surprise, that Oregon White that CAC makes took glazes the best( the description under it is still wrong).....especially celadons....gorgeous detail showing through. Glazes also did not tend to run on it like the other procelains.....Frost and the New Zealand one. A glaze I really liked is Skim Milk I got off glazy....very nice white buttery matte that stays put. Bet it does well with drawing.  I am still working on the stonewares.....not a surprise that that raku body had a lot of problems....pin holes, crawling etc. Bennett, B mix and OH were the others. B mix appeared to take glazes very well. I just don't like working with it. OH is CAC;s answer to B mix. It throws well but did not take glazes as well as B mix.  Do you know of a truly white stoneware? They all are some variation of buff. 

I have a cone 10 reduction glaze called Brown Cow....I always wondered why the hell anyone would ever use it.....it was just an ugly clear dark brown.....it's a substitute for albany slip isn't it? That you are supposed to put another glaze over like chun?  It doesn't turn red....it just sits there being very dark brown almost black.

[Min]

4 hours ago, MFP said:

Yes....I was suspicious that 3 was barium carbonate. I used a lot of it in a celadon glaze I used....a lot . I was wondering if it started to fuse at that temp, I think my memory is going....I thought digital fire said it would not lose mass on LOI but that could not be possible because it is a carbonate....perhaps I measured it incorrectly.  It also is somewhat lumpy and likes to form balls. 

It does have an LOI but it gets it by either being melted with other materials, like in a glaze recipe, or alone it needs to get to 1460C so in your bisque firing it shouldn't have had an LOI. It's been years since I've had barium in my studio, can't remember if it agglomerates (forms clumps or balls).

4 hours ago, MFP said:

Who has the cheapest tin?

I don't know but I buy mine from US Pigments online. 

4 hours ago, MFP said:

I also have a coffee can full of something that is either zircopax or tin.

If you make up that high calcium glaze recipe and to 100 grams of it add 5 tin plus 0.15 (that's zero point 15) chrome oxide you will get a raspberry colour.

4 hours ago, MFP said:

It had a slight opacifying effect and made the glaze somewhat more glossy. 

Titanium dioxide maybe. 

4 hours ago, MFP said:

Do you know of a truly white stoneware?

Porcelain. Whitest stoneware I've used is White Salmon from Georgies but the absorption is too high for me. 

[MFP]

Ok...then I think 3 is barium carbonate.  I have some barium in a jar....and it looks similar. Looks like what I need to do is what I did with the three oxides....I put known oxides on a chip with glaze and then the three unknowns on three other chips and numbered them.  Finally differentiated the cobalt from the nickel from the black iron.  So. looks like time to throw more small cups and in the next bisque, put in small amounts of common materials we suspect they are and the unknowns again. Then we should be able to figure it out. 

I have also discovered that melting point and actually melting are two different things. I had an experiment  in the last fire.....garnet sand in the bottom of a dish with clear Mayco glaze. Yes....it was clearly starting to melt at 6  but not melted. So it's going to have to go to 9 at least to be melted together. 

I should note that aside from the coffee can, these are large cans of materials....about five gallons worth....so they would not contain anything that was used in small quantities. I already found the titanium oxide.....so know that #2 is not that.  The reason I think the coffee can may be tin is because I made the white glaze with it and it was whiter....does that make any sense?

I saw US Pigments also....will check it out again. 

I think it is ironic that I have found three porcelain clay bodies that all have their pros and cons, but still cannot settle on a stoneware body. It seems like everyone has switched to porcelain. 

Thank you again so very much for all your time!  You are very generous!! 

[neilestrick]

I did not read this discussion in detail, but 1 and 5 are doing the ash glaze rivulet thing, so likely high in calcium.

 

37 minutes ago, MFP said:

 

I think it is ironic that I have found three porcelain clay bodies that all have their pros and cons, but still cannot settle on a stoneware body. It seems like everyone has switched to porcelain. 

 

In regards to white stoneware: A lot of people treat white stoneware as a gateway clay for porcelain, the thought being that it's smooth like porcelain but supposedly easier to work with and therefore a good transition from groggy stoneware to smooth porcelain. In truth, it behaves nothing like porcelain, and has (IMO) none of the properties that make porcelain so unique and great. White stoneware is higher in clay, and typically high in ball clay, so the plasticity is completely different and usually too high. It's often more prone to S-cracks as a result. It doesn't feel at all the same when trimming, because the density is totally different. The color is whiter than a typical grey or brown stoneware, so glaze colors pop a little more, but nothing like the porcelain pop. I think people realize that they're not getting what they hope for, and just move on to porcelain. Personally, I don't really see the sense in using a white stoneware if you've got a porcelain body you like. Find a good brown stoneware so you get some real contrast, or just work in porcelain. Standard 112 is a wonderful speckled brown if I may make a recommendation.

[MFP]

THANK YOU!  I thought I was losing my marbles.....I actually have found the porcelains easier to work with than these stoneware bodies!   And Yes!  I have been battling s cracks in the stoneware but not getting them in the porcelain---despite compressing and compressing and compressing.  I certainly saw in this fire that the colors do much better on the porcelain.....and that Oregon White, although it looks slightly tan where the exposed body is....under the glaze it is strikingly white.  It also did not have areas of uneven appearing glaze like the New Zealand and Frost did. I also noted that glazes like Floating Blue and Wright's Water Blue liked to run on the other two but not on the Oregon White. I am glad I put that extra coat of kiln wash on!

B mix took glazes well but I hate it. It seems to have all the disadvantages of porcelain and none of the benefits. Ironically, the cone 10  Amaco stoneware is very nice to work with but way too expensive. I bought it before I had shopped around.

Well....this answers my question then. CAC makes two traditional stoneware bodies recommended for oven ware....they are your classic grey body with grog. They have one version for 6 and another for 10...again I liked the 10 version better.  It took glazes well in this testing. So....if I want to make oven ware...that's my choice.

So I am thinking that stoneware is staying in the cone 10 group. 

I took back that raku body and replaced it with the Oregon White....so porcelain it is!  ( I told them they had the wrong description under that clay listing but they never  changed it) It is their best selling body,  The porcelain bodies are sure different now. The only one I worked with in the past was Kai from Westwood and it was very challenging. 

Thanks again!  This answered a lot of questions!

[MFP]

Yes....I noticed that....I am wondering if this is all due to the Colemanite.  I am going to put a bunch of cups with "knowns" in the next bisque and all four unknowns again and see if we get any matches!  As I told Min, we did not use the wide range of materials then that people use now.  So picking five or six of the most common should not be that hard.

[neilestrick]

@MFP You say you like the cone 10 version better than the 6. Do you have the option of firing 6 or 10? What type of kiln are you firing in?

[MFP]

I have a little 1827H Olympic electric that I am NEVER going to ask to fire to cone 10----the one with the gaping lid.. My plan was spending the summer/fall learning cone 6 oxidation. I also have a huge  2831/2381 ( I can never remember) Olympic propane kiln that has never been fired. I first have to deal with the burners....they are rusted on the outside and I have a feeling that it is going to take some effort and lots of WD40 to open up the ports....if they even have them.....they call this kiln Torchbearer now....but mind has 6 burners not 4. I also have to set up the propane line. I wanted to wait til this winter to fire it as I do not want to vent it.....all I have to do here in the winter is open the shop door and all the heat will be sucked out right away! ( I am in northern Idaho). It is going to take a lot of ware to fill that thing up....and I must admit I am ambivalent about it. But I still have all my cone 10 glazes and there are now so many cool cone 10 refection glazes to try!  And cone 10 reduction is what I know.....and now having porcelains you can actually  use for cone 10? Heaven!   

I like the color possible at 6 oxidation....and the subtly at cone 10 reduction.    I already have separate shelves set up for the different bisque ware.