Simon Heath

Clever. Thank you!

Thank you, yes, ultimately this is how I would like to do it, but the fit on the last few I've thrown has been too snug to do this. I think this is how I will have to do it going forward. S.

Thank you - I agree that I don't think it's mould. Odd colour, and not on the butter at all, just the unglazed part exposed to water. The stated porosity is 1% at cone 6 and I tend to fire high, more like a cone 7 (the cone 7 cone is always completely bent over). Will try CLR. S.

Hi there, People have been so helpful in the past, I wonder if I could ask for some more help. I have a french butter dish that I made with bright white porcelain (porcelaineous) with simple clear 5/20 glaze. I fired the two pieces separately as I was worried they would fuse together. This means, there is an unglazed rim on the interior piece, which is exposed to the water (but not the butter). That unglazed rim has developed a weird blue green colour (as seen in photo). Does anyone have any idea what this is? It's fired to cone 6 and I would have thought vitrified the clay. Could it be from the water? Any thoughts appreciated! Simon

Thank you both. It's funny, I'm struggling a bit with this programmable kiln, because of its consistency. My old kiln, there was almost a full cone difference between the bottom and top shelves. Some of my glazes like it hotter than others. I had learned to load the kiln based on results through years of trial and error. But it was small (21X18) and manual, so now I'm trying to learn my new kiln. It's a Cone Art and has a coil on the bottom, so my cone packs are almost identical top and bottom (haven't tested middle, there are three thermocouples). Ideally, I'd be able to get a full kiln load of a particular glaze and fire it to its preference, but the new kiln is much bigger (23x27) and takes me close to two months to fill, depending on life! But this is all part of the learning process, and your input is so valuable! As for the drop, yes, I got the error on 9999, talked to a kiln tech and he suggested 500/hr. I went overly conservative and tried 300, with no error, so maybe I will try to bump it up a bit to 400/hr. Will see if there's any improvement and check back to post. S.

Thank you again, both! I'm amazed at the generosity of the people on this forum. I will drop it to a slow bisque (I had already gone from 06 to 04 to try to address pinholes). I've just moved from a manual kiln sitter to programmable, so still figuring it out. I originally dropped it at 9999/hr, but got an error code for it being above the target temperature and was told to go for a less aggressive rate of cooling. So, that's why I'm dropping at 300/hr, which hasn't triggered the error. Dumb question - is the only way to fire to cone 5 1/2 to manually enter the target temperature? In my current firing cycle, I program peak temperature as cone 6 (and yes, it definitely looks like cone 7, though that is the top shelf of the kiln). Thank you for the links on Campana - the grey definitely looks much greyer than mine. I might actually try the recipe without the manganese, just the small amounts of cobalt and copper (assuming I ever get this existing bucket of glaze sorted). S.

Thanks everyone. No, the tiny amounts of cobalt and copper probably aren't an issue, just trying not to dump glazes in my backyard. Thanks Madeleine. Despite having read several books on glazes (several times), I still struggle with the chemistry. I see the silica to alumina ratio has changed slightly along with the COE and LOI, but don't know how to adjust. The thing is, I got the pinholes on a standard programmed cone 6 slow glaze fire and did the slow cool with holds to try to fix the problem. Below are photos from the slow cool firing. Running isn't a huge problem - two of the three pots shown are fine.

Okay, thank you, I think I can work this out to calculate dry glaze material in the sample volume. But is the fix to just add in the Manganese carbonate, more EPK and silica, or does the effect of the magnesium carbonate (I've become convinced that's what I did) need to be offset? Thank you! S.

Hoo boy - very appreciative of your response, but trying to wrap my head around it! No idea how much water, though it was 5 kg of dry material to approx. 145 sp gravity, is there any way to calculate based on that? Do I have to weigh my water? Rural area with quite hard water. Just to clarify your suggestion - 180 glaze and only mang. carb, silica and EPK? Not copper carb and cobalt carb and all the other ingredients? And does the (probably) magnesium carbonate's effect on the glaze need to be counterbalanced? I don't use glaze software, so my level of sophistication is somewhat limited. Yes, I do find the cone pack shows it reaches cone 7 - my other glazes are very diverse (Tenmoku Gold tea dust; a high calcium matte variegated blue from Mastering Cone 6 glazes, 5x20 and a few others - although I did notice some pinholes in a cream rust that I've never had pinholes in before). My slow cool firing was to try to get rid of pinholes, not create them! Also, trying to grow crystals in Binger, but that's another story. Yes, calls for carbonate, not dioxide - I have a different glaze that uses the very black manganese dioxide. Thank you - you're very generous with your responses. S.

Thank you Madeleine! I would certainly love to save it if I could. The manganese/magnesium thought makes a lot of sense. The glaze is Campana Grey (recipe below), pretty well-known glaze, it did run a lot, but the recipe says it tends to anyway so I just assumed it was the recipe. I have long battled pinholes and seem to have fixed them with all my other glazes - I fast bisque to 04, blast the bisqueware with an air compressor before glazing and have a slow cool firing schedule of: 108 degrees/hr to 220; 350/hr to 2000; 108/hr to cone 6 - 10 min hold; 300/hr to 2100 - 20 min hold; 300/hr to 1900 - 15 min hold; 150/hr to 1400. I've used it on both Bright White porcelain and Mid Cal 5 stoneware (both Tuckers, Canada), pinholes on both, but worse on the stoneware Campana Grey 3134 - 21% EPK - 20% Silica 20% Wollastonite 20% Spodumene 11% Zinc Oxide 8% ---- Manganese Carb 1.8% Copper Carb 0.6% Cobalt Carb 0.15%

Hi there, I'm hoping for some advice. I recently mixed up a 5 kg batch of glaze. Lots of pinholes. I just realized the 1.8% Manganese Carbonate I used wasn't Manganese Carbonate. I don't know what I used - fluffy white powder (ha!), maybe Lithium carbonate, but who knows. Since the glaze contains cobalt carbonate and copper carbonate, and there is so much of it (too much to fire into bricks), I'm thinking my only choice is to see if the local waste management landfill will take it under their Hazardous Household Waste program. Any other suggestions? Thanks in advance, Simon