Rick Wise Posted February 27, 2018 Report Share Posted February 27, 2018 Can anyone tell me why I am getting blistering at the bottom (only) of the piece when using this homemade glaze? Its called Westcountry Water and is: Silica 36 Potclays/BPS High Alkaline Frit 30.5 Devon China Clay 20 Gillespie Borate 12 Whiting 1.5 Total Base Recipe 100 Zircopax 4 Bentonite 3 Copper Carbonate 2 Total 109 Otherwise, a very satisfactory glaze. Link to comment Share on other sites More sharing options...
dhPotter Posted February 27, 2018 Report Share Posted February 27, 2018 I would guess it is too thick. The glaze may have slid down the pot and gathered making it too thick. Waterfall Brown from MC6 will do this. Link to comment Share on other sites More sharing options...
LeeU Posted February 28, 2018 Report Share Posted February 28, 2018 I think it is gorgeous! I would love to get that happening (it's a style thing). Link to comment Share on other sites More sharing options...
neilestrick Posted February 28, 2018 Report Share Posted February 28, 2018 @Rick Wise What cone are you firing? It's difficult say say exactly what's going on without knowing the makeup of that frit. Running the formula with a few different US frits, it's possible that it's high in silica, high in boron, or high in calcium. Any chance you have the formula for that frit? The Potclays web site doesn't have any information on it. Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted February 28, 2018 Report Share Posted February 28, 2018 Hey @neilestrick, does this link maybe help? (I can't run the recipe myself.) https://digitalfire.com/4sight/material/potclays_frit_2275_2435.html It's the only one listed distinctly as high alkaline. Link to comment Share on other sites More sharing options...
Sputty Posted February 28, 2018 Report Share Posted February 28, 2018 . Link to comment Share on other sites More sharing options...
neilestrick Posted February 28, 2018 Report Share Posted February 28, 2018 @Rick Wise Turns out I have that frit in my materials index! With the correct frit, I'm not seeing anything particularly worrisome about that glaze. It's at the high end for silica, and the sodium is a little high, but nothing that would point to what's happening in your photos. Are you sure it wasn't under fired? Did you sieve the glaze well before applying? Link to comment Share on other sites More sharing options...
Benzine Posted March 1, 2018 Report Share Posted March 1, 2018 19 hours ago, neilestrick said: @Rick Wise Turns out I have that frit in my materials index! With the correct frit, I'm not seeing anything particularly worrisome about that glaze. It's at the high end for silica, and the sodium is a little high, but nothing that would point to what's happening in your photos. Are you sure it wasn't under fired? Did you sieve the glaze well before applying? Any time I've run into similar issues, it was because of underfiring/ cooling relatively quickly. Link to comment Share on other sites More sharing options...
Rick Wise Posted March 21, 2018 Author Report Share Posted March 21, 2018 On 2/27/2018 at 8:36 PM, neilestrick said: @Rick Wise What cone are you firing? It's difficult say say exactly what's going on without knowing the makeup of that frit. Running the formula with a few different US frits, it's possible that it's high in silica, high in boron, or high in calcium. Any chance you have the formula for that frit? The Potclays web site doesn't have any information on it. Sorry -- no idea on the formula. I fire to cone 6. BTW, the picture is deceptive as to color. It is a light green with a hint of blue in it. Link to comment Share on other sites More sharing options...
Magnolia Mud Research Posted March 21, 2018 Report Share Posted March 21, 2018 A recent set of posts in another thread reminded me that clay bodies can contribute to glaze blistering. The specific reason for the blisters is that gas is trying to migrate through a very stiff melt. The root cause will be found when you chase all the possible sources of gas formation, not just the sources in the glaze. The mug appears to have a thicker wall at the bottom than at the top. Also there seems that the number of blisters per unit area increases from the top to the bottom. This pattern is consistent with the clay body not being fully free of gas producing 'stuff'. Try the glaze on a different clay body using the same glaze. Critique the bisque firing protocol, especially for the time at burnout temperatures. Thicker walls require longer to burnout times than thin walled items. Also a full kiln takes longer to burnout than a not-so-full kiln. From the glaze side, look carefully at the initial melt temperature of the glaze based on the specific ingredients. Frits often begin to fuse together at lower temperatures than non-fritted components. LT Link to comment Share on other sites More sharing options...
Joe_L Posted March 21, 2018 Report Share Posted March 21, 2018 5 hours ago, Rick Wise said: ... I fire to cone 6. ... What clay are you using? I guess you're in the UK using those ingredients - there has been debate on here about how many UK commercial stoneware clays are actually suitable for ^6. Quite a few seem to be marketed with wide temperature ranges which may be misleading. Link to comment Share on other sites More sharing options...
Min Posted March 23, 2018 Report Share Posted March 23, 2018 On 3/21/2018 at 9:12 AM, Rick Wise said: I fire to cone 6. BTW, the picture is deceptive as to color. It is a light green with a hint of blue in it. I agree with what Magnolia Mud Research has said about looking at your firing schedules, both for bisque and glaze firings. Do you use witness cones to verify the firings? I found this image of the same glaze, looks vastly different from yours. I know you said your picture is deceptive but there is a huge difference between your glaze surface and the one from the link. Given the silica:alumina ratio I would expect it to be a high gloss when fired to maturity. Leaves me to think that you have two issues going on here, firstly the bisque firing wasn't thorough enough to burn out all the gas producing materials and secondly the glaze firing didn't get hot enough. Clean and slow bisque firing with as much ventilation as you can get, (vent the kiln or peeps out for most of the firing if you don't have a vent) to cone 04 plus verify your glaze firing with cones, add a soak just below your top temperature to allow time for the pinholes and blisters to heal and smooth over. Link to comment Share on other sites More sharing options...
Babs Posted March 23, 2018 Report Share Posted March 23, 2018 I also wonder if after stirring bubbles are forming on top of glaze in bucket. I did have this prob with one glaze and when fired the bubles deposited on ware did not go away on firing unless fettled, or as Min? suggested at time, sprayed glaze in bucket with hairspray to dissipate bubbles before the dip... Link to comment Share on other sites More sharing options...
Babs Posted March 23, 2018 Report Share Posted March 23, 2018 the bubbles were most evident at foot of pot and edge of dip Link to comment Share on other sites More sharing options...
Rick Wise Posted March 28, 2018 Author Report Share Posted March 28, 2018 On 3/21/2018 at 4:49 PM, Joe_L said: What clay are you using? I guess you're in the UK using those ingredients - there has been debate on here about how many UK commercial stoneware clays are actually suitable for ^6. Quite a few seem to be marketed with wide temperature ranges which may be misleading. Standard 112 and 306. US Link to comment Share on other sites More sharing options...
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