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I made some confirmationish discoveries with my currie grid test in results to SiC. I have said it before but I sort confirmed it today.  I have said in the past that glazes that have more flux s

Well, I got my slab roller setup this weekend and I went out and bought 2 dollars worth of kids play foam. I ended up building this:   Which is three square foams thick. The triangle on

I finally got round to using a couple of Currie grids in my last firing. I varied alumina and iron instead of adding kaolin and silica, so I hope no-one minds me posting in this thread. The tiles are

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I dont understand where the book gets its numbers from. He list a bunch of percents for the grid tiles, then later the math he provides doesn't match at all with those percents. It's rather odd.

For example the limestone set.

He list 70 Feldspar 30 Whiting.

For glaze 1. The amount of Flux Materials should be: 60%. Thus feldspar: 60% * 70 = 42.00, whiting: 60% * 30 = 18.00. This is what the book list. Then the very next glaze is out of wack.

For glaze 2. The amount of Flux Materials should be 54%. Thus feldspar: 54% * 70 = 37.80, whiting: 54% * 30 = 16.20. But the book has: 37.63, and 16.13. How in the world is he doing his math? Makes 0 sense.

Even his Kaolin/Silica numbers don't make sense. It is like he didn't stick to the basis that he posted on page 32 which has the % kaolin, silica and flux materials for each grid. Somehow he moves off those numbers slightly?

I have been just using these numbers assuming they are correct. But it doesn't appear to be so unless I am missing something here. 

I mean I guess it doesn't matter much since they are just decimals off, but still I don't like puzzles. I also noticed several of his grids don't add up to 100%.... on page 32. Grid 28,13 and 7.

Edit: Now I think I see is going on. way to make some things really complicated by not just showing % + decimal. meh....

Edited by Joseph F
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Well. I finished my spreadsheet.

If anyone wants to use it because the currie sheet is all bonker: https://docs.google.com/spreadsheets/d/1faETrVYo0Lin_2LU7GYK2BgvOuVLf3cCpefjQzRC5ns/edit?usp=sharing

The green areas are the place you input data. There is no complicated rules for entering data. Just put in the amount of flux directly from your recipe in grams, same for colorants. I couldn't think of any recipe with over 6 fluxes I have ever used, so I just went with 6. 

I have also included my addition method in case anyone wants to use it. I use it so I incorporated it here. 

Once you put in your data, click to the spreadsheet on the bottom called: Currie PrintOut. It will have all your information there. Just print it. Done.

My copper SiC tiles are cooking. I will post the tiles tomorrow. Let's hope the Alumina Silica stuff holds true again.

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On 11/6/2017 at 2:25 PM, Joseph F said:

It is an iron red glaze. I am not really sure what color it is. Depending on the light it changes drastically. It can be pink, yellowish, red, orange. Of course on a tile things can be very misleading. The next step is to mix up a slightly larger batch and dip a small cup and spray a larger one. I was waiting to pickup my son and I took the tile with me to look at in the daylight.  I am not  sure if I like the glaze or not yet. Once I spray and dip on more I will know.

It really is hard to show the colors. Its reddish black in a dark room, but like this in the cloudy sun. The main thing I want to think about is the difference between the SiC and the non SiC. Really wild.



Awesome color.  It reminds me of the results/ effects I get with some of my Raku glazes, which is one reason I like it.  Is that for functional wares?

If it doesn't have an official name, you need to give it one.  Based on my experience with the commercial glazes, the names don't always have to make sense.  There was color I ordered called "Tabacco Brown", but it was an off white, with small flecks of brown.  So it looked more like tabacco spit brown...

Edited by Benzine
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@Benzine No plans to name it. If anything I might use it on some vases or something, but I doubt it is safe for using for food. Considering it has 30% Iron Oxide in it. lol. I have to presume it will change the flavor of the food drastically. I just glaze two cups with it, and that is probably the last I will ever use it. I need to focus on one thing and explore it deeply. I probably wont be doing anymore currie grids for a few months.


As promised here are the results from the currie grid test of the copper sic glaze: (left is base, right is 1.2% SiC).


My favorite is grid 11. The greenish blue with red specks is very nice. I would say that my most favorite is 16, but it crazes slightly. 17 also has some merit.

I changed the recipe from the original in johns book. I didn't have enough Frit 3110, so I went with 3134, which lowered the SiO2 amount drastically. Which I was ok with since I wanted the lower bounds of the limit. However I think it might have overfluxed. I don't know. Anyways. 

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On 07/11/2017 at 2:39 PM, curt said:

Seems that molten iron (and also cobalt and nickel) is an excellent solvent for silicon carbide, starting at temperatures well below the stoneware maturing range.  Maybe the iron-heavy glaze mixture is simply decomposing the silicon carbide early and often, preventing it from delivering the usual cratering?  And, giving it that nice smooth satin matte texture.

Maybe what this guy suggested?   Just substitute the word “copper” for “iron”?  Lol.  Maybe.  

However, looks like those right hand side SiC cells are kind of pittted, no?

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I broke it in half on the tile I was talking about earlier. It definitely has places that look like bubbles. I don't have a microscope camera so the picture is pointless, but when I hold up a magnifying glass to it, it has bubbles below the surface. But still, do I care about those bubbles? I mean the surface is still smooth isn't that the goal for the work? Although I could care less about those tiles on the right hand side. The best tiles are 16,17 and 21. I am actually going to develop those glazes further I think and add more SiC. I think it could handle upwards of 2-3% SiC cause at 1.2 it shows 0 signs of bubbling and very little red dotting. But this is going to be for a later time. I have another glaze I am about to spend a few months documenting thoroughly. 

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A few more comments after a second careful look at these two copper/SiC tiles.  I do like the second, third and fourth looks, because I am less distracted by colours and better able to hunt for the patterns and other fruit currie is offering up.

First, suggest if possible you treat SiC as a flux in your calcs for this glaze.  My take is that the second tile is overall noticeably more fluxed than the base tile.  Specifically, compare cells 16 and 21 on both tiles.  The SiC tile is much more crazed in those cells, making it more like its neighbours below. To me crazing is a sign of excessive flux (or, lol, not enough alumina and silica :-)) .  In fact, overall the entire first column is much more fluxed on the SiC tile. 

Also, the whole right hand two columns of each tile compared, where we see the base tile very bubbly and crusty, and the same columns on the SiC tile smoothed out - pitted and bubbled yes (as you would expect with greater fluxing?) - but nonetheless flattened out, like the melt has been better or more complete anyway.

On a "standard" currie tile with "standard" fluxes I think you would normally be looking for the "best" quality glass in cells 13, 14 and 15,  and in cells 18, 19 and 20, where the alumina and silica are in about the right ratio, and with the right amount of flux to get the job done.  However, in both your tiles, the good glass cells are much father over to the left as you have identified.  This suggests to me that this glaze is very silica sensitive, and too much silica is just not a viable glaze, or more specifically, does not produce a good homogenous melt.  

Finally, very interesting to see where the red is in the SiC tile.  At high flux levels, there simply is NO reduction red appearing.  In fact, you could almost draw a line across the tile from the upper left to the lower right as the "reduction boundary", ie, combinations of silica and alumina that DO allow the reduction affect to occur, ie, where you can see red just starting to appear.   Interestingly, at the bottom of this boundary, in the bottom row of the  SiC tile, the red only appears in cell 34.  Maybe it would have appeared in cell 35, but looks like this cell may not have melted properly.

This all suggests to me that there is minimum silica and alumina that is needed to produced SiC copper red?  Also, that this glaze is VERY sensitive to silica....


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@curt I agree with most of that, with some exceptions:

- The picture might not show it but there is little red specks in each of the high flux tiles, that said they are nothing like the red appearing in the right corner as you said. I personally like the red dots on the crazed surface. I actually have plans to use that as it is such a rare thing to see, a blueish green glaze with red specks. Very pretty. 

- I thought SiC was refractory.  It would require some good flow test to actually prove that it is "fluxing" the glaze. I might be up for that eventually but I have some other plans to work on. That being said I don't really understand either how the surfaces are better on the SiC tile. I also did .4 and .8 SiC as well I just didn't post them. They have the same increasing properties. As SiC increases between the tiles the cells get smoother and smoother. The red from the oxygen theft isn't that much more apparent when increasing the SiC by 100% each time. It would be interesting to preform a flow test with something like 0% SiC 1% 2% 3% 4% just to see if in fact it is refractory at some point but some other chemical process is happening that is causing the glaze to "flow" or "glass" better. The smoothing of the cells definitely happens as I increase SiC. Looking at tiles .4, .8 and 1.2 you can literally see the smoothing effect happening  when looking at all three in order. I will attach .4 and .8 below.  

- The pictures don't show it well, but the crazing is slightly decreasing in the SiC tiles, as would be expected as you are increasing the ratio of silica to flux. (I will try to add a better picture that shows the crazing.)

I will start posting pictures hosted via my webserver instead of the upload in the future, because it is hard to make assumptions like the ones we have made with crappy resolution pictures. Sorry about that.

My theory is that the smoothness comes from the Silica in the SiC. I think it is balancing the alumina and silica ratios ever so slightly so that the glaze is more stable. But this is just a theory. All the right hand rows, even though some are smoother look underfired to me.  The reason I believe this is because the only corner that doesn't seem to care about the SiC is corner D, and the tiles around it. It looks pretty much the same from every tile. 




Crazing Picture: I cropped the close up pictures. As you can see the SiC is actually reducing the crazing, which makes sense considering it is comprized of mostly silica right? I hosted this one on my webserver so you can click it a few times to get to the actual source and see it in higher res.


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34 minutes ago, Pieter Mostert said:

Reduction makes iron a more powerful flux, so if the same is true for copper, that would explain why the SiC tiles appear more fluxed. But I don't know if this is the case.

I totally agree on this point. I know iron is a flux in reduction, but I am not sure that this is the case with copper. I have never read that anywhere, but I don't fire reduction so again I could be wrong. But it doesn't account for the crazing improving slightly as more SiC is added. That would be opposite factor I would assume? 

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I was thinking along those lines Pieter, maybe the SiC is adding more power to the other flux.

There's no need to care about the bubbles but it is good to know they are still in the glaze and probably trapped by it being really viscous.


Looking at the tiles it seems to me like the SiC is more like alumina than anything else, the high silica tiles with a little become more like a glaze you would find top left not bottom right. 



Iron reduction is to do with Fe2O3 > FeO  Red iron oxide > black iron oxide



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i have noticed when firing crystalline glazes that high percentages of cobalt would make the glaze boil. Although, the 25% zinc addition has to be considered as well. However, high copper additions always retained a smooth finish. Relative??? Just an observation. I have played with SiC in cone six red recipes. It seems to favor calcium and potash in a melt.

i have had better success with SiC when I chemically reduce it beforehand: which I will not discuss here. Mr. baymore made a very logical point in another thread recently about the forum audience. 

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Just in case you haven't read it yet the Tom Turner article on Chemically Reduced Copper Reds in Oxidation has all sorts of tantalizing clues, like "Chemicals such as tin, zinc, magnesium, iron, phosphorous, sulphates and of course any material containing carbon are hungry for oxygen and will help reduce the glaze colourants as they melt" Also, "I found that as the silicon carbide size became smaller, there was more glaze melt, less surface texture from the glaze bubbling while giving off oxygen during the chemical processes and weaker reduction."

BTW in oxidation firings I've found cobalt, copper and manganese act as fluxes.

Edited by Min
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@Min I read through his document several times. Lots of really good information.

That last sentence you pasted: "I found that as the silicon carbide size became smaller, there was more glaze melt, less surface texture from the glaze bubbling while giving off oxygen during the chemical processes and weaker reduction." 

I think this has a lot of merit to look into. I am curious if I can increase the SiC amounts greatly since the surface is suffering from less bubbling from the finer meshes of SiC. I wonder if you can increase it and still have a smoother surface but start to get the same reduction effects. Eventually I will test this. Maybe in the coming weeks. Particularly around the perfect Silica and Alumina ratios that seem to promote the reduction but not the surface bubbles.

For the others:

Is there a general interest for me to continue posting these SiC grids? I am going to be running a bunch of them along side normal grid test every few weeks. I will start posting the higher resolution pictures in the future however.  If people feel like I am just posting useless information by posting my grids I will stop linking them. I find them interesting, but maybe this isn't the place to continue to link them? 

I am also going to adapt my grid this week as well to have more information in the cells, some type of vertical change. Also they will be more uniform thanks to my new slab roller coming.

Edited by Joseph F
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