Lance Hall
New Member
Lance Hall, married to Maureen, StillPoint Pottery
Posts: 17
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Post by Lance Hall on May 30, 2016 16:01:05 GMT -6
I'm having problems recently with pinholes, mostly on mugs and such where we have used a basic white liner glaze ("Limestone white" which contains Custer, silica, whiting and such) and a Glaze containing Fusion Frit 413. The pinholes are right at the top of the mug where the liner glaze and the crystalline glaze meet and flows down the pot a bit when the two glazes melt together.
These pinholes have a sharp edge so I'm guessing that they formed towards the end of the firing schedule and they didn't have time to smooth over, but I'm not sure. The crystalline glaze itself has no pinholes and neither does the liner glaze. I have tried a few other liner glazes (one with Minspar, the others with Custer) but the problem persists. I am using Plainsman H570 clay which I've used a long time both in reduction and crystalline.
Any suggestions and or ideas?
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Post by jfox on May 30, 2016 22:03:33 GMT -6
add about 10 minute soak just as the cone drops without letting the temp go up anymore
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annie
Junior Member
Posts: 55
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Post by annie on Jun 1, 2016 1:58:40 GMT -6
Hi Lance, Holding longer should heal the pinholes or some of them, however from personal experience you may also consider some or all of the following: Increasing the silica amount in your liner glaze (try 3-5grams per 100g dry mix) to stiffen the liner (even just at the rim if you wish), load up the rim more thickly with liner, avoid overlapping your crystalline glaze over or under the liner (just put it right to the edge of the outside liner-glazed rim), and the final thing that fixed all my rim pin-hole problems is change clay! I found, after much headache and hassle, that until I switched to the smoothest stoneware clay I could get I always got at least some pinholes or raised bits, from grog or Molocite maybe, on rims where the liner and crystalline met. Testing other clays and many tweaks of liner glazes revealed the best and most complete solution was switching to a super smooth clay (plus I still increased silica in the liner and pay attention to not overlap at the rim). This is just another challenge we each face with crystalline glazing. Now that I've solved this, I'm cooking on gas as they say! Good luck, but do consider getting some test quantities of clays and see if that's your biggest hurdle re pinholes. Annie  |
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Lance Hall
New Member
Lance Hall, married to Maureen, StillPoint Pottery
Posts: 17
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Post by Lance Hall on Jun 1, 2016 10:08:56 GMT -6
Hi Annie and thanks for your suggestions.
So I dipped the tops of my pots in some more glaze and refired them. Lo and behold, no pinholes! Yes
So here is what I think; I think that I am having an interection between the liner glaze and the crystalling glaze AND I think the glaze was too thin on the rims. Interestingly, Maureen sprayed her mugs upside down while I sprayed mine right side up. Hers had almost no pinholes.
I will do more testing and post the results.
Lance
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annie
Junior Member
Posts: 55
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Post by annie on Jun 1, 2016 11:36:16 GMT -6
That's fabulous Lance!
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timhanrahan
New Member
Still growing crystals!
Posts: 22
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Post by timhanrahan on Jun 10, 2016 20:53:23 GMT -6
Hi Lance,
I have had similar problems, fortunately on vases where it is less critical to have a little roughness on the rim. I also suspected a problem with the crystal and liner glazes. My solution was a little less technical though.... I make sure that I sponge off all the liner glaze from the rims and put a thick coat of crystal glaze on the rim. I always do the liner glaze the day before and let them dry before applying the crystal glaze. Good luck next firing.
Tim
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timhanrahan
New Member
Still growing crystals!
Posts: 22
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Post by timhanrahan on Jun 11, 2016 9:05:05 GMT -6
oops dupe
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