Raise firing temperature of high thermal expansion glaze

[Kelly in AK]

Aw rats! Just when I think I know what I’m talking about something comes up to remind me I’ll always be learning. It’s why, I too, love this community. I forgot the vigor with which copper carbonate creates bubbles. Definitely could opacify. The good Tony Hansen has done work showing this property, perhaps there’s something useful for you in there:

https://digitalfire.com/material/copper+carbonate

Edit: rereading the thread suggests you’ve seen this article already, so apologies if it’s redundant. Micro-bubbles suddenly seemed at least as culpable as crystallization. Hansen acknowledges decomposing copper off gasses wickedly, but also attributes bubbles to kaolin in the glazes on some of his tiles. Also useful could be this, even though it’s dealing with cone 6:

https://insight-live.com/insight/share.php?show=ruY3muruhJ1

Finally, 3110 is a high expansion low alumina frit. I stay away from it precisely because it’s a craze monster. Very fluid, could pass bubbles easily. 

Edited June 12, 2023 by Kelly in AK

[mr_glazy_man]

Hi all,

Big update. Image attached of results. 

I have conducted line blends of the following base (Copper Carb - 5% is added to all by default) and fired to 1040. Fast cool. All glaze weights were measured to ensure even application across the tile and equal amounts between tiles. 

Base

FZ-16 - 90%

EPK - 10%

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Column 1 (Biaxial):

3134 - 85%

EPK - 15%

Notes: Didn't notice any difference at all between the blends. Important to note that this was a double line blend, not 10% addition of 3134. Again, opacification around the edges of the test tile, which is what I was getting with the FZ-16 Base at 1040.

------------------------------------------

Column 2:

+2.5% Additions of Wollastonite

Notes: As we go up, opacification increased. This is a similiar result to the EPK. We conclude here the additions of calcium does not resist copper or zinc's opacification in this base.

------------------------------------------

Column 3:

+2.5% Additions of Whiting

Notes: Big blisters. Likely a result of the LOI of whiting. Again, opacification of the copper.

------------------------------------------

Column 4:

+2.5% Additions of Strontium Carb

Notes: I was curious what this would give me, even though Strontium Carb isn't an active flux at these low temperatures (unless in frit form, which I don't have). Interestingly enough, the strontium resisted the opacification but there are a score or mirco-bubbles under the surface. This is likely the later LOI of Strontium Carb.  Overall, unsatisfactory finish.

 

Well, after all that, no movement towards the goal of getting FZ-16 to melt at 1040 the way it does at 960 or even 1000. 

Any ideas? I might have a go at line blending with 3110 which is a lower boron and thus higher melting frit.

Edited June 16, 2023 by mr_glazy_man
Formatting and placement of image

[Min]

This is going to be a tough nut to crack. You demonstrated really well the off-gassing of calcium carb though. Looks like the wollastonite turned the colour more towards blue than green which is also interesting. Good testing procedure. I wonder how much stain the glaze could take before loosing the depth of colour you are getting from the copper. Just spitballing an idea, wonder if you used part stain with a higher melting glaze and blended it with your original copper high fritted zinc glaze. Compromise between depth of colour and temp?

[mr_glazy_man]

Quote

I wonder how much stain the glaze could take before loosing the depth of colour you are getting from the copper. 

Me too. I'll give it a shot with a line blend with some Turquoise stain. 

If I'm not so bloody rigid and just fire my ware at 1000 for this particular base, it's basically problem solved. And, it's a magical finish. 40 degrees (celcius) is literally what is separating me from where I am now and Leadless-Copper Valhalla. 

 

Edited June 16, 2023 by mr_glazy_man
SPECIFICITY!

[Kelly in AK]

Ahhhh. The best solution. Find something that works and stick with it.

No one can say you didn’t try, that’s for sure! I appreciate you sharing that journey. 

[mr_glazy_man]

Success! 

I am happy to say that because of all of your wonderful help, I have been able to get this glaze right. Hats off to @Min for the suggestion of blending 3110 with the base glaze. 
 

The end result is an absolutely marvellous turquoise that fires at exactly 1040c and without a single defect. And, completely and utterly leadfree. The only thing I need to really work out now is how to increase the crazing.

I’m working on getting the exact proportions correct, but see below attached photo. Base on the left, 3110 on the right. You can see that the host really needs the fritted zinc (not raw zinc oxide) to delay melting, otherwise surface problems.

 

Edited June 19, 2023 by mr_glazy_man
Punctuation

[Min]

10 hours ago, mr_glazy_man said:

The end result is an absolutely marvellous turquoise that fires at exactly 1040c and without a single defect. And, completely and utterly leadfree. The only thing I need to really work out now is how to increase the crazing.

Really good to hear you got the colour you wanted!

For increasing the crazing the simplest thing to do would be to dunk the hot pieces into cold water. Don't know if this is an option with the the scale of work you do?

I was thinking about your suspension comment you made a few posts back. If all else fails there is a product called MAGMA that will suspend even clay free glazes. There are caveats with it though; it isn't widely available (made by Bracker's Good Earth Clays in the US), it thickens the slurry plus it slows down the dry time. I use it now and then, it really works.

[mr_glazy_man]

@Min Never heard of Magma. Alas, just tried ordering it online and they don’t ship down under. Rats!

Cold dunking wouldn’t be an option with our line, but maybe a cold blast of air right out of the kiln might work on a larger scale. I’ll be sure to post back here if I give it a go.

Thank you again all.

[PeterH]

It might be interesting to try a crazing test on your test-tiles, such as

IWCT - 300F:Ice Water Crazing Test
https://digitalfire.com/test/iwct

If only to judge the effect of any changes you make to the recipe/firing.

Edited June 19, 2023 by PeterH

[Babs]

CMC GUM do the same?

 

[PeterH]

A couple of minor points if you are still trying to increase the crazing.

1) Always ink-up (part of) your test-tiles. It can sometimes be hard to see the true extent of the crazing. It also gives you a better idea of the number of cracks which occur after the initial inking.

an example from Digitalfire

 

2) I understand that glaze programs are not too accurate at estimating the absolute COE of a glaze, but  they are quite good at estimating the change to the COE that small change to the recipe/chemistry will make. So maybe you are reaching the point where they might be useful.

See Using Calculation to Fit a Glaze in https://digitalfire.com/article/understanding+thermal+expansion+in+ceramic+glazes

Edited June 20, 2023 by PeterH

[Min]

15 hours ago, Babs said:

CMC GUM do the same?

MAGMA and CMC gum have some of the same qualities but they are not the same. 

Good chart here showing the qualities of many glaze suspenders and additives. What the chart doesn't show is how the glaze applies with CMC vs MAGMA when dipped. The latter doesn't  cause the drips/curtaining when used in dipping glazes.