mr_glazy_man

Got it. I have FZ16 and FZ14 line blends to try and fix this - a zinc based frit will likely help. Will let you know how I go!

I’m so glad you posted those links, I’m hung up on exactly this as well. If decomposition happens at 320C, I would certainly not be having the issues I’m having because my high fluxed (read: high boron) glazes begin to melt at around 750-800C. The idea behind the zinc is to have them melt much later and more vigorously, at cone 05-06, but the exact amount depends on when the decomposition phase ends!

I don’t get pinholes in my later melting copper glazes, but I am getting them in my own earlier melting copper glazes. I need to be firing at exactly 1000°C, so I my idea is to incorporate a zinc to delay melting and give the copper an opportunity to finish off gassing. As a matter of curiosity, what temperature does copper typically finish its offgassing?

@PeterH Copper Oxide gives me dark specks. The carbonate is much more finely milled and gives a more uniform colour @Min good to know. I might go the non cadmium green and mix it with black and a pinch of blue to get a more emerald green. I’m too scared of poisonous cadmium!

Hi, A number of posts back I was talking about a beautiful 04 fluid melt glaze I created with FZ16 and 3110. Doing a line blend between Iron Oxide and Copper Carb in this base yields a lovely green, but I feel like it needs more punch. Increasing the amount of oxide colourant just causes more bubbles and glaze defects due to the amount of off gassing (I’m at 5% Copper already!) So, I’m thinking about cutting it with some green stain to reduce the LOI, increase the green saturation but still get that oxide depth we all know and love. Alas, I’m sure most of you now know where this is going - most green stains are chrome based, and chrome+zinc is…. well, brown ain’t green. Can anyone recommend a non-chrome based green stain? Another tact might be Green Iron Oxide, which though is not stain based, may dial up the saturation of green but I really haven’t found much info in this at all online. What do you all think?

@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.

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.

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.

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% ------------------------------------------ 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.

Ugh, amazing. I love this community. Thank you - that’s incredibly helpful. If you don’t mind me asking - is there a resource you pulled this from? I’d love to get my hands on it! In terms of the double variable test - this would be a biaxial, correct? In such a case, I will test with: A: FZ-16 90% EPK 10% Copper Carb - 5% B: 3134 - 80% FZ-16 - 10% EPK 10% Copper Carb - 5% Im hesitant to go 20% EPK again because of how thick it was last time with the FZ-16. I ended up using Tetrasodium Pyrophosphate and CMC to deflocculate, slow drying a little just to make it workable. I’m weary of adding too much extra water, because it’ll dilute my S.G and aiming for gram weights on the ware will mean a lot of glaze I don’t want. I might also try another test with my initial base recipe and 2% increments of wollastonite. However, the unwanted added silica in the wollastonite has me thinking that whiting - as bob suggested - might be preferable. Besides, the zinc and it’s late melt should give time for the calcium carb to off gas properly. Time will tell I suppose. Maybe I’ll do both. I can’t say, because I haven’t tested on any curved geometry - only test tiles. But the glossiness and ability to heal over defects absolutely rivals lead bisilicate, just as he said. This is why I’m so keen to get the temp up - if I can get it to 1040, I’m grinning. Sadly not, but this has me thinking that I might want to invest in one now.

@Min Ah, but it’s the beautiful oxide transparency that I want. Stains just don’t look the same i am using glaze calc, but without having limit guides for earthenware (every target formula seems to be for cone 6) it just feels like I’m shooting in the dark. For calcium, I was initially thinking Wollastonite, but you’re right, frit form would be better. 3134 has close to 20% calcium, so I could line blend with that. Would you have any other suggestions?

3134 and 3124 is another interesting avenue, for sure. I feel like that one, in addition to the magnesium based 3249, are both candidates to do line blends with (though the 3249 will have the opposite effect to crazing). The reason I test across the temperature range is to observe how a material behaves under different intensities of heat. It’s laborious, but enables me to visually distinguish symptoms of under and over firing. I’ll be playing with a number of other permutations of materials this week and I’ll post the update. Thank you for the compliments!

Unfortunately I’m at an odd’s end as to why the copper is opacifying at all - I haven’t been able to find anything on Digital Fire or other adjacent sites that suggest anything about copper opacification. @BobMagnuson provided a nice trail to follow with the suggestion that it might be the zinc opacifying, but it doesn’t explain the opacification in other hosts - which leads me to suspect that this is specifically related to the copper.

Broadly speaking, the higher I go in temperature, the more likely the opacification (depending on the base glaze I’m using). I would have thought that firing cycle is, in this instance, a negligible variable. I could be wrong on this of course.

@Bill Kielb I fire the kiln at the ramp cycle recommendations set out in the Orton Self Supporting Cones chart to verify correct heat work and temperature. If I get the corresponding 90Degree bend, then my temperatures are correct Do you suspect an incorrect temperature that might be causing the copper’s opacification?