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Post by Russ White on Oct 19, 2015 14:28:56 GMT -6
Good Day everyone, Long time no chat. I've been plugging along, here in California. On my last two firings ,I've been getting blisters on ten percent of my pieces. The only thing I changed is a higher temperature soak and made it more of a slant soak. On the second firing I changed the after peek ramp cool down ,to last longer. I was thinking if the bubbles had more time to pop and smooth out the problem would be solved. It didn't. I could me be answering my own question here. The only change is the firing.    Here is is my firing schedule. The two cones you see are ^11 on the left ^ 10 on the right.  Any Ideas |
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Post by Arnie Benton on Oct 19, 2015 16:41:07 GMT -6
Hi Russ!
I'm glad you're back - I just did a reread on blistering from various sites - I won't go through all they talk about - from bisque firing too low to wet glazes to gases escaping from metal carbonates or feldspars - on the one hand your glaze seems to have a lot of running down, but there isn't much in the catcher. I imagine that's a stoneware glaze on the bottom? It seems logical that bubbles would occur in thick or viscous glazes - but they also occur with excessively fluid glazes. Maybe something to do with soaking at such a high temp? I don't see any crystals. What kind of effect are you trying to produce?
Arnie
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Post by mohawkpiper on Oct 19, 2015 18:22:20 GMT -6
I am with Arnie on the excessively fluid glazes.
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Post by Russ White on Oct 20, 2015 14:16:29 GMT -6
Thanks for the input Arnie & Greg. I've been walking the tight rope lately. Always trying to push things. Bisque is not the problem. Same firing for the last seven years ^04. Arnie ,good observation on glaze flow. The last year I have been experimenting with glaze thickness and glaze melt and how it effects the final product. I've been playing with different frits ,frit combos, lithium carb etc... The question you asked is what I'm trying to achieve. 1. The right thickness on glaze application 2. The right melt with that application 3. Ax heads crystals with the right amount of crystals verses background. In other words, I want it all  . Here is one example. The pot on the right came from my last firing and is what I'm looking for, but at the expense of 10% lose due to blisters. Look at the green glaze ,soon to turn to aqua blue glaze. The glaze is just thin enough to let the white porcelain clay body to show through.  I'm going to lower my soak temp and ether raise my peek temp or increase my hold at peek. keep you posted. Russell |
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Post by mohawkpiper on Oct 20, 2015 15:51:56 GMT -6
Russ,
Forgive me if I have this wrong, but I believe you want to do the opposite.
Blisters can come from an excessively fluid glaze. By raising the peak temp or holding longer at peak you are increasing the fluidity of the glaze, not helping the blisters at all.
I think you want to lower your peak temp, or hold less at peak to make the glaze less fluid. Should help with the pinholing.
Then you risk loosing your aqua blue color and raise your chances of getting that green color again.
So perhaps to solve this make your application slightly thinner. If you can get a pretty even coat (eg spraying) then you have less of a chance of getting bare spots or discolored spots when going thinner on the application.
If that works generally a thinner coat during the crystal growing phase will give you rounder crystals (not always, but most of the time) so to solve that raise your hold temp. Lowering your hold temp will give you even rounder crystals.
If that doesn't work perhaps you can try subbing the lithium for some boron (gerstley borate) but generally I feel like boron promotes blistering more than lithium. Or swapping just a little of the frit for a frit that melts a little more.... then there is that fine line....
Just my .02
G
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Post by mohawkpiper on Oct 20, 2015 16:02:57 GMT -6
ps. We have a similar looking glaze we call teal. (Our crystals are blue though as opposed to green.) It has been the most changing throughout the years and that aqua blue color (we refer to as teal) is what we strive for with it. It is difficult to get it to cover the whole pot (unless on a shorter piece) and the greener color usually comes through at the bottom. The green color seems to just want to come out more, unless we make it more fluid, but then we get the pinholing occasionally. We recently (6 months to a year ago) bought a batch of 3110 that seems to be much more fluid than usual and with a mix of the not so fluid 3110 and the fluid 3110 we are back on schedule. Most of the time. Here it is on flat...  G |
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Post by Russ White on Oct 20, 2015 17:59:21 GMT -6
Hey G,
You're correct about the hold temp & time. Unfortunately, when I lower my crystal growth temp I feel (don't know) I need to counter that heat work loss with something. When I lower growth temps, I get blah green again. The kiln is really packed this time. It will take a lot of heat work to get this baby cookin. I will take that under consideration. If I blow it ,it will be a bummer. On the other hand, nothing ventured nothing gained.
I'm going to light the candle tonight.
Wish me luck
Russell
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Post by evan cornish-keefe on Oct 21, 2015 8:18:33 GMT -6
I've had pinholes when using clay bodies that were being fired too hot, the clay was starting to bloat too, lowering the top temp half a cone really improved this without significantly affecting the glaze. Your pinholes may be caused by something different but it seems like crystalline glazes are already "over-fired" so more heat work wouldn't help.
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Post by tileman2 on Oct 21, 2015 16:55:56 GMT -6
Can always add .25 - .50% antimony oxide- long used in the glass blowing biz to keep bubbles and pinholes out.
Tom
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Post by Russ White on Oct 22, 2015 21:06:04 GMT -6
Hello everyone, Well ,the results are mixed. No pinholes or blisters. That's the good news. The bad, I put the throttle down to hard. I burned off too many nuclei. Too few crystals and the ones that are there are too small. Oh well, I love playing the game. Figuring it out is the fun for me. Tom, thanks for the tip on the Antimony Oxide. I'll give it a go, if I run into this problem again. I do think , my main problem was over firing. Here is a pic from the last firing.  Thanks for the input Russell |
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paul
Junior Member
Posts: 51
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Post by paul on Jun 1, 2016 21:01:11 GMT -6
Russ,
Quite a while back I got some nice turquoise from copper with Barium Carbonate added.
As you know it is a flux, but it also modifies the color.
If you knew that already, Oh well...
Of Course Barium is not a healthy material to say the least
Best Regards
Paul
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annie
Junior Member
Posts: 55
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Post by annie on Jun 3, 2016 3:29:14 GMT -6
Hi guys,
Strontium can also modify your copper to give you a nice turquoise, but it's a flux too and I've had to counter it's power with less frit or more silica. It'll slide right off porcelains and all the crystals end up in the catcher.by the way, I'm liking the look! Annie
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Aymen
New Member
Posts: 10
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Post by Aymen on Jun 15, 2017 1:15:50 GMT -6
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